Hello,
syzbot found the following issue on:
HEAD commit: ac3a0c84 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11b8d570900000
kernel config: https://syzkaller.appspot.com/x/.config?x=e59ee776d5aa8d55
dashboard link: https://syzkaller.appspot.com/bug?extid=305a91e025a73e4fd6ce
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11f7ceea900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17e5de04900000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]
IPVS: ftp: loaded support on port[0] = 21
==================================================================
BUG: KASAN: use-after-free in hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
Read of size 8 at addr ffff8880a9591f18 by task syz-executor081/6793
CPU: 0 PID: 6793 Comm: syz-executor081 Not tainted 5.8.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1f0/0x31e lib/dump_stack.c:118
print_address_description+0x66/0x5a0 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report+0x132/0x1d0 mm/kasan/report.c:530
hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
l2cap_conn_del+0x4c2/0x650 net/bluetooth/l2cap_core.c:1900
hci_disconn_cfm include/net/bluetooth/hci_core.h:1355 [inline]
hci_conn_hash_flush+0x127/0x200 net/bluetooth/hci_conn.c:1536
hci_dev_do_close+0xb7b/0x1040 net/bluetooth/hci_core.c:1761
hci_unregister_dev+0x16d/0x1590 net/bluetooth/hci_core.c:3606
vhci_release+0x73/0xc0 drivers/bluetooth/hci_vhci.c:340
__fput+0x2f0/0x750 fs/file_table.c:281
task_work_run+0x137/0x1c0 kernel/task_work.c:135
exit_task_work include/linux/task_work.h:25 [inline]
do_exit+0x601/0x1f80 kernel/exit.c:805
do_group_exit+0x161/0x2d0 kernel/exit.c:903
__do_sys_exit_group+0x13/0x20 kernel/exit.c:914
__se_sys_exit_group+0x10/0x10 kernel/exit.c:912
__x64_sys_exit_group+0x37/0x40 kernel/exit.c:912
do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x444fe8
Code: Bad RIP value.
RSP: 002b:00007ffe96e46e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000444fe8
RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001
RBP: 00000000004ccdd0 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 00007f5ee25cd700 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006e0200 R14: 0000000000000000 R15: 0000000000000000
Allocated by task 6821:
save_stack mm/kasan/common.c:48 [inline]
set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc+0x103/0x140 mm/kasan/common.c:494
kmem_cache_alloc_trace+0x234/0x300 mm/slab.c:3551
kmalloc include/linux/slab.h:555 [inline]
kzalloc include/linux/slab.h:669 [inline]
hci_chan_create+0x9a/0x270 net/bluetooth/hci_conn.c:1692
l2cap_conn_add+0x66/0xb00 net/bluetooth/l2cap_core.c:7699
l2cap_connect_cfm+0xdb/0x12b0 net/bluetooth/l2cap_core.c:8097
hci_connect_cfm include/net/bluetooth/hci_core.h:1340 [inline]
hci_remote_features_evt net/bluetooth/hci_event.c:3210 [inline]
hci_event_packet+0x1164c/0x18260 net/bluetooth/hci_event.c:6061
hci_rx_work+0x236/0x9c0 net/bluetooth/hci_core.c:4705
process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
Freed by task 1530:
save_stack mm/kasan/common.c:48 [inline]
set_track mm/kasan/common.c:56 [inline]
kasan_set_free_info mm/kasan/common.c:316 [inline]
__kasan_slab_free+0x114/0x170 mm/kasan/common.c:455
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x220 mm/slab.c:3757
hci_disconn_loglink_complete_evt net/bluetooth/hci_event.c:4999 [inline]
hci_event_packet+0x304e/0x18260 net/bluetooth/hci_event.c:6188
hci_rx_work+0x236/0x9c0 net/bluetooth/hci_core.c:4705
process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
The buggy address belongs to the object at ffff8880a9591f00
which belongs to the cache kmalloc-128 of size 128
The buggy address is located 24 bytes inside of
128-byte region [ffff8880a9591f00, ffff8880a9591f80)
The buggy address belongs to the page:
page:ffffea0002a56440 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8880a9591800
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002a5a648 ffffea00028a4a08 ffff8880aa400700
raw: ffff8880a9591800 ffff8880a9591000 000000010000000a 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff8880a9591e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880a9591e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880a9591f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880a9591f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880a9592000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at [email protected].
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches
Hi,
This is SyzScope, a research project that aims to reveal high-risk
primitives from a seemingly low-risk bug (UAF/OOB read, WARNING, BUG, etc.).
We are currently testing seemingly low-risk bugs on syzbot's open
section(https://syzkaller.appspot.com/upstream), and try to reach out to
kernel developers as long as SyzScope discovers any high-risk primitives.
Please let us know if SyzScope indeed helps, and any suggestions/feedback.
Regrading the bug "KASAN: use-after-free Read in hci_chan_del", SyzScope
reports 3 memory write capability.
The detailed comments can be found at
https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-hci_chan_del
On 8/2/2020 1:45 PM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: ac3a0c84 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11b8d570900000
> kernel config: https://syzkaller.appspot.com/x/.config?x=e59ee776d5aa8d55
> dashboard link: https://syzkaller.appspot.com/bug?extid=305a91e025a73e4fd6ce
> compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11f7ceea900000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17e5de04900000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email protected]
>
> IPVS: ftp: loaded support on port[0] = 21
> ==================================================================
> BUG: KASAN: use-after-free in hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
> Read of size 8 at addr ffff8880a9591f18 by task syz-executor081/6793
>
> CPU: 0 PID: 6793 Comm: syz-executor081 Not tainted 5.8.0-rc7-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x1f0/0x31e lib/dump_stack.c:118
> print_address_description+0x66/0x5a0 mm/kasan/report.c:383
> __kasan_report mm/kasan/report.c:513 [inline]
> kasan_report+0x132/0x1d0 mm/kasan/report.c:530
> hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
> l2cap_conn_del+0x4c2/0x650 net/bluetooth/l2cap_core.c:1900
> hci_disconn_cfm include/net/bluetooth/hci_core.h:1355 [inline]
> hci_conn_hash_flush+0x127/0x200 net/bluetooth/hci_conn.c:1536
> hci_dev_do_close+0xb7b/0x1040 net/bluetooth/hci_core.c:1761
> hci_unregister_dev+0x16d/0x1590 net/bluetooth/hci_core.c:3606
> vhci_release+0x73/0xc0 drivers/bluetooth/hci_vhci.c:340
> __fput+0x2f0/0x750 fs/file_table.c:281
> task_work_run+0x137/0x1c0 kernel/task_work.c:135
> exit_task_work include/linux/task_work.h:25 [inline]
> do_exit+0x601/0x1f80 kernel/exit.c:805
> do_group_exit+0x161/0x2d0 kernel/exit.c:903
> __do_sys_exit_group+0x13/0x20 kernel/exit.c:914
> __se_sys_exit_group+0x10/0x10 kernel/exit.c:912
> __x64_sys_exit_group+0x37/0x40 kernel/exit.c:912
> do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x444fe8
> Code: Bad RIP value.
> RSP: 002b:00007ffe96e46e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000444fe8
> RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001
> RBP: 00000000004ccdd0 R08: 00000000000000e7 R09: ffffffffffffffd0
> R10: 00007f5ee25cd700 R11: 0000000000000246 R12: 0000000000000001
> R13: 00000000006e0200 R14: 0000000000000000 R15: 0000000000000000
>
> Allocated by task 6821:
> save_stack mm/kasan/common.c:48 [inline]
> set_track mm/kasan/common.c:56 [inline]
> __kasan_kmalloc+0x103/0x140 mm/kasan/common.c:494
> kmem_cache_alloc_trace+0x234/0x300 mm/slab.c:3551
> kmalloc include/linux/slab.h:555 [inline]
> kzalloc include/linux/slab.h:669 [inline]
> hci_chan_create+0x9a/0x270 net/bluetooth/hci_conn.c:1692
> l2cap_conn_add+0x66/0xb00 net/bluetooth/l2cap_core.c:7699
> l2cap_connect_cfm+0xdb/0x12b0 net/bluetooth/l2cap_core.c:8097
> hci_connect_cfm include/net/bluetooth/hci_core.h:1340 [inline]
> hci_remote_features_evt net/bluetooth/hci_event.c:3210 [inline]
> hci_event_packet+0x1164c/0x18260 net/bluetooth/hci_event.c:6061
> hci_rx_work+0x236/0x9c0 net/bluetooth/hci_core.c:4705
> process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
> worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
> kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
>
> Freed by task 1530:
> save_stack mm/kasan/common.c:48 [inline]
> set_track mm/kasan/common.c:56 [inline]
> kasan_set_free_info mm/kasan/common.c:316 [inline]
> __kasan_slab_free+0x114/0x170 mm/kasan/common.c:455
> __cache_free mm/slab.c:3426 [inline]
> kfree+0x10a/0x220 mm/slab.c:3757
> hci_disconn_loglink_complete_evt net/bluetooth/hci_event.c:4999 [inline]
> hci_event_packet+0x304e/0x18260 net/bluetooth/hci_event.c:6188
> hci_rx_work+0x236/0x9c0 net/bluetooth/hci_core.c:4705
> process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
> worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
> kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
>
> The buggy address belongs to the object at ffff8880a9591f00
> which belongs to the cache kmalloc-128 of size 128
> The buggy address is located 24 bytes inside of
> 128-byte region [ffff8880a9591f00, ffff8880a9591f80)
> The buggy address belongs to the page:
> page:ffffea0002a56440 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8880a9591800
> flags: 0xfffe0000000200(slab)
> raw: 00fffe0000000200 ffffea0002a5a648 ffffea00028a4a08 ffff8880aa400700
> raw: ffff8880a9591800 ffff8880a9591000 000000010000000a 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff8880a9591e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8880a9591e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> ffff8880a9591f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff8880a9591f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880a9592000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at [email protected].
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
Hi Dan,
Sorry for the confusing. This bug was reported by a normal syzbot email.
What we are trying to do is discovering more primitives such as memory
write or function pointer dereference hidden behind the primitive shown
on syzbot(which is a memory read in hci_chan_del() in this case).
We realized that some primitives may not be found by fuzzing because of
the heap layout. By symbolizing the UAF/OOB memory and perform a
symbolic execution, we are able to go deeper in the buggy code instead
of encountering kernel panic(NULL pointer dereference from UAF/OOB
memory) or complicated constraints that prevent fuzzing from entering.
In our measurement, we found that memory write bugs are usually fixed
faster than memory read bugs or non-security bugs(e.g., WARNING). Thus,
we think evaluating the real impact of a bug helps people understand the
how risky the bug really is and benefit the patching process.
Regarding this bug, syzbot originally reported a memory read primitive
(KASAN read in hci_chan_del()). In the detailed comments URL, we are
showing that we find a memory write primitive using the same PoC on
syzbot, we believe the memory write primitive makes the bug more risky.
On 05/05/2021 23:01, Dan Carpenter wrote:
> On Tue, May 04, 2021 at 02:50:03PM -0700, ETenal wrote:
>> Hi,
>>
>> This is SyzScope, a research project that aims to reveal high-risk
>> primitives from a seemingly low-risk bug (UAF/OOB read, WARNING, BUG, etc.).
>>
>> We are currently testing seemingly low-risk bugs on syzbot's open
>> section(https://syzkaller.appspot.com/upstream), and try to reach out to
>> kernel developers as long as SyzScope discovers any high-risk primitives.
>>
>> Please let us know if SyzScope indeed helps, and any suggestions/feedback.
>>
>> Regrading the bug "KASAN: use-after-free Read in hci_chan_del", SyzScope
>> reports 3 memory write capability.
>>
>> The detailed comments can be found at https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-hci_chan_del
>>
> I don't understand what you are saying at all. This looks like a normal
> syzbot email. Are you saying that part of it generated by SyzScope?
> I don't think there is anyone who thinks a UAF/OOB read is low impact.
>
> There are no comments at the "detailed comments" URL.
>
> regards,
> dan carpenter
>
>> On 8/2/2020 1:45 PM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following issue on:
>>>
>>> HEAD commit: ac3a0c84 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
>>> git tree: upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=11b8d570900000
>>> kernel config: https://syzkaller.appspot.com/x/.config?x=e59ee776d5aa8d55
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=305a91e025a73e4fd6ce
>>> compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11f7ceea900000
>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17e5de04900000
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> Reported-by: [email protected]
>>>
>>> IPVS: ftp: loaded support on port[0] = 21
>>> ==================================================================
>>> BUG: KASAN: use-after-free in hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
>>> Read of size 8 at addr ffff8880a9591f18 by task syz-executor081/6793
>>>
>>> CPU: 0 PID: 6793 Comm: syz-executor081 Not tainted 5.8.0-rc7-syzkaller #0
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>> Call Trace:
>>> __dump_stack lib/dump_stack.c:77 [inline]
>>> dump_stack+0x1f0/0x31e lib/dump_stack.c:118
>>> print_address_description+0x66/0x5a0 mm/kasan/report.c:383
>>> __kasan_report mm/kasan/report.c:513 [inline]
>>> kasan_report+0x132/0x1d0 mm/kasan/report.c:530
>>> hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
>>> l2cap_conn_del+0x4c2/0x650 net/bluetooth/l2cap_core.c:1900
>>> hci_disconn_cfm include/net/bluetooth/hci_core.h:1355 [inline]
>>> hci_conn_hash_flush+0x127/0x200 net/bluetooth/hci_conn.c:1536
>>> hci_dev_do_close+0xb7b/0x1040 net/bluetooth/hci_core.c:1761
>>> hci_unregister_dev+0x16d/0x1590 net/bluetooth/hci_core.c:3606
>>> vhci_release+0x73/0xc0 drivers/bluetooth/hci_vhci.c:340
>>> __fput+0x2f0/0x750 fs/file_table.c:281
>>> task_work_run+0x137/0x1c0 kernel/task_work.c:135
>>> exit_task_work include/linux/task_work.h:25 [inline]
>>> do_exit+0x601/0x1f80 kernel/exit.c:805
>>> do_group_exit+0x161/0x2d0 kernel/exit.c:903
>>> __do_sys_exit_group+0x13/0x20 kernel/exit.c:914
>>> __se_sys_exit_group+0x10/0x10 kernel/exit.c:912
>>> __x64_sys_exit_group+0x37/0x40 kernel/exit.c:912
>>> do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
>>> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>> RIP: 0033:0x444fe8
>>> Code: Bad RIP value.
>>> RSP: 002b:00007ffe96e46e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
>>> RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000444fe8
>>> RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001
>>> RBP: 00000000004ccdd0 R08: 00000000000000e7 R09: ffffffffffffffd0
>>> R10: 00007f5ee25cd700 R11: 0000000000000246 R12: 0000000000000001
>>> R13: 00000000006e0200 R14: 0000000000000000 R15: 0000000000000000
>>>
>>> Allocated by task 6821:
>>> save_stack mm/kasan/common.c:48 [inline]
>>> set_track mm/kasan/common.c:56 [inline]
>>> __kasan_kmalloc+0x103/0x140 mm/kasan/common.c:494
>>> kmem_cache_alloc_trace+0x234/0x300 mm/slab.c:3551
>>> kmalloc include/linux/slab.h:555 [inline]
>>> kzalloc include/linux/slab.h:669 [inline]
>>> hci_chan_create+0x9a/0x270 net/bluetooth/hci_conn.c:1692
>>> l2cap_conn_add+0x66/0xb00 net/bluetooth/l2cap_core.c:7699
>>> l2cap_connect_cfm+0xdb/0x12b0 net/bluetooth/l2cap_core.c:8097
>>> hci_connect_cfm include/net/bluetooth/hci_core.h:1340 [inline]
>>> hci_remote_features_evt net/bluetooth/hci_event.c:3210 [inline]
>>> hci_event_packet+0x1164c/0x18260 net/bluetooth/hci_event.c:6061
>>> hci_rx_work+0x236/0x9c0 net/bluetooth/hci_core.c:4705
>>> process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
>>> worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
>>> kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
>>> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
>>>
>>> Freed by task 1530:
>>> save_stack mm/kasan/common.c:48 [inline]
>>> set_track mm/kasan/common.c:56 [inline]
>>> kasan_set_free_info mm/kasan/common.c:316 [inline]
>>> __kasan_slab_free+0x114/0x170 mm/kasan/common.c:455
>>> __cache_free mm/slab.c:3426 [inline]
>>> kfree+0x10a/0x220 mm/slab.c:3757
>>> hci_disconn_loglink_complete_evt net/bluetooth/hci_event.c:4999 [inline]
>>> hci_event_packet+0x304e/0x18260 net/bluetooth/hci_event.c:6188
>>> hci_rx_work+0x236/0x9c0 net/bluetooth/hci_core.c:4705
>>> process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
>>> worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
>>> kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
>>> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
>>>
>>> The buggy address belongs to the object at ffff8880a9591f00
>>> which belongs to the cache kmalloc-128 of size 128
>>> The buggy address is located 24 bytes inside of
>>> 128-byte region [ffff8880a9591f00, ffff8880a9591f80)
>>> The buggy address belongs to the page:
>>> page:ffffea0002a56440 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8880a9591800
>>> flags: 0xfffe0000000200(slab)
>>> raw: 00fffe0000000200 ffffea0002a5a648 ffffea00028a4a08 ffff8880aa400700
>>> raw: ffff8880a9591800 ffff8880a9591000 000000010000000a 0000000000000000
>>> page dumped because: kasan: bad access detected
>>>
>>> Memory state around the buggy address:
>>> ffff8880a9591e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>> ffff8880a9591e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>>> ffff8880a9591f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>> ^
>>> ffff8880a9591f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>> ffff8880a9592000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>> ==================================================================
>>>
>>>
>>> ---
>>> This report is generated by a bot. It may contain errors.
>>> See https://goo.gl/tpsmEJ for more information about syzbot.
>>> syzbot engineers can be reached at [email protected].
>>>
>>> syzbot will keep track of this issue. See:
>>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>>> syzbot can test patches for this issue, for details see:
>>> https://goo.gl/tpsmEJ#testing-patches
>>>
>> --
>> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group.
>> To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
>> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/c2004663-e54a-7fbc-ee19-b2749549e2dd%40gmail.com.
Sorry for the confusion on our last email. We did a little more analysis
after then and hope to help developers fix this bug.
The bug was reported by syzbot first in Aug 2020. Since it remains
unpatched to this date, we have conducted some analysis to determine its
security impact and root causes, which hopefully can help with the
patching decisions.
Specifically, we find that even though it is labeled as "UAF read" by
syzbot, it can in fact lead to double free and control flow hijacking as
well. Here is our analysis below (on this kernel version:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/?id=af5043c89a8ef6b6949a245fff355a552eaed240)
----------------------------- Root cause analysis:
--------------------------
The use-after-free bug happened because the object has two different
references. But when it was freed, only one reference was removed,
allowing the other reference to be used incorrectly.
Specifically, the object of type "struct hci_chan" can be referenced in
two places from an object called hcon(or conn in hci_chan_create)of type
struct hci_conn : "hcon->chan_list" and "hcon->l2cap_data->hchan". But
only one of them (conn->chan_list) was deleted when freeing "struct
hci_chan" from "hci_disconn_loglink_complete_evt()".
The function "hci_chan_create" shows how the first reference is created.
struct hci_chan *hci_chan_create(struct hci_conn *conn)
{
struct hci_dev *hdev = conn->hdev;
struct hci_chan *chan;
...
chan = kzalloc(sizeof(*chan), GFP_KERNEL);
...
list_add_rcu(&chan->list, &conn->chan_list); // Assign chan to
hcon->chan_list. This is the first reference created.
return chan;
}
"l2cap_conn_add" is the caller of the previous function which shows how
the second reference is created.
static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon)
{
struct l2cap_conn *conn = hcon->l2cap_data;
struct hci_chan *hchan;
...
hchan = hci_chan_create(hcon); //"hchan" was created in hci_chan_create
if (!hchan)
return NULL;
conn = kzalloc(sizeof(*conn), GFP_KERNEL);
...
kref_init(&conn->ref);
hcon->l2cap_data = conn;
conn->hcon = hci_conn_get(hcon);
conn->hchan = hchan; // "chan" was assigned to
"hcon->l2cap_data->hchan". This is the second reference.
...
}
When the chan was freed in "hci_disconn_loglink_complete_evt"
(hci_disconn_loglink_complete_evt()->amp_destroy_logical_link()->hci_chan_del()),
we only deleted the reference of "((struct hci_conn *)hcon)->chan_list"
(effectively removing the entry from the list), but the reference of
"((struct hci_conn *)hcon)->l2cap_data->hchan" is still valid.
The function below shows exactly how the free of the object occurs and
how its first reference is removed.
void hci_chan_del(struct hci_chan *chan)
{
struct hci_conn *conn = chan->conn;
struct hci_dev *hdev = conn->hdev;
BT_DBG("%s hcon %p chan %p", hdev->name, conn, chan);
list_del_rcu(&chan->list); // removed "chan" from the list (the
first reference). The second reference((struct hci_conn
*)hcon->l2cap_data->hchan) remains however.
synchronize_rcu();
set_bit(HCI_CONN_DROP, &conn->flags);
hci_conn_put(conn);
skb_queue_purge(&chan->data_q);
kfree(chan); // free "chan"
}
----------------------------- Potential fix: --------------------------
Based on the analysis, it appears that in hci_chan_del(), we should
remove the second reference of (struct hci_conn
*)hcon->l2cap_data->hchan,e.g., setting it to NULL
-------------------------- Control flow hijacking Primitve:
-----------------------------
This function is where the bug impact was originally reported on syzbot
void hci_chan_del(struct hci_chan *chan) //"chan" was freed
{
struct hci_conn *conn = chan->conn; // Syzbot reported the UAF read
struct hci_dev *hdev = conn->hdev;
...
skb_queue_purge(&chan->data_q); // "data_q" comes from the freed
object "chan" therefore it can point to an arbitrary memory address
kfree(chan);
}
The skb was dequeued from the list, however the list is controllable by
an attacker and it can point to an arbitrary memory address.
void skb_queue_purge(struct sk_buff_head *list)
{
struct sk_buff *skb;
while ((skb = skb_dequeue(list)) != NULL) // skb is also controllable
kfree_skb(skb); // dangerous use of skb further down
}
After going through a long call chain:
skb_queue_purge->kfree_skb->__kfree_skb->skb_release_all->skb_release_data,
skb enters "skb_zcopy_clear".
static void skb_release_data(struct sk_buff *skb)
{
...
skb_zcopy_clear(skb, true); // skb entered skb_zcopy_clear() and
will dereference a function pointer inside.
skb_free_head(skb);
}
static inline void skb_zcopy_clear(struct sk_buff *skb, bool zerocopy)
{
struct ubuf_info *uarg = skb_zcopy(skb); // uarg comes from skb,
therefore it also controllable by attacker
if (uarg) {
if (skb_zcopy_is_nouarg(skb)) {
/* no notification callback */
} else if (uarg->callback == sock_zerocopy_callback) {
uarg->zerocopy = uarg->zerocopy && zerocopy;
sock_zerocopy_put(uarg); // uarg enters sock_zerocopy_put()
}
...
}
}
Inside the function below, uarg's function pointer will be dereferenced.
This makes a control flow hijacking possible because uarg is totally
controllable by attackers.
void sock_zerocopy_put(struct ubuf_info *uarg)
{
if (uarg && refcount_dec_and_test(&uarg->refcnt)) {
if (uarg->callback)
uarg->callback(uarg, uarg->zerocopy); // uarg dereferences
a function pointer, and thus we grant a control flow hijacking primitive
...
}
}
SyzScope Team.
On 8/2/2020 1:45 PM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: ac3a0c84 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11b8d570900000
> kernel config: https://syzkaller.appspot.com/x/.config?x=e59ee776d5aa8d55
> dashboard link: https://syzkaller.appspot.com/bug?extid=305a91e025a73e4fd6ce
> compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11f7ceea900000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17e5de04900000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: [email protected]
>
> IPVS: ftp: loaded support on port[0] = 21
> ==================================================================
> BUG: KASAN: use-after-free in hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
> Read of size 8 at addr ffff8880a9591f18 by task syz-executor081/6793
>
> CPU: 0 PID: 6793 Comm: syz-executor081 Not tainted 5.8.0-rc7-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x1f0/0x31e lib/dump_stack.c:118
> print_address_description+0x66/0x5a0 mm/kasan/report.c:383
> __kasan_report mm/kasan/report.c:513 [inline]
> kasan_report+0x132/0x1d0 mm/kasan/report.c:530
> hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
> l2cap_conn_del+0x4c2/0x650 net/bluetooth/l2cap_core.c:1900
> hci_disconn_cfm include/net/bluetooth/hci_core.h:1355 [inline]
> hci_conn_hash_flush+0x127/0x200 net/bluetooth/hci_conn.c:1536
> hci_dev_do_close+0xb7b/0x1040 net/bluetooth/hci_core.c:1761
> hci_unregister_dev+0x16d/0x1590 net/bluetooth/hci_core.c:3606
> vhci_release+0x73/0xc0 drivers/bluetooth/hci_vhci.c:340
> __fput+0x2f0/0x750 fs/file_table.c:281
> task_work_run+0x137/0x1c0 kernel/task_work.c:135
> exit_task_work include/linux/task_work.h:25 [inline]
> do_exit+0x601/0x1f80 kernel/exit.c:805
> do_group_exit+0x161/0x2d0 kernel/exit.c:903
> __do_sys_exit_group+0x13/0x20 kernel/exit.c:914
> __se_sys_exit_group+0x10/0x10 kernel/exit.c:912
> __x64_sys_exit_group+0x37/0x40 kernel/exit.c:912
> do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x444fe8
> Code: Bad RIP value.
> RSP: 002b:00007ffe96e46e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 0000000000444fe8
> RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001
> RBP: 00000000004ccdd0 R08: 00000000000000e7 R09: ffffffffffffffd0
> R10: 00007f5ee25cd700 R11: 0000000000000246 R12: 0000000000000001
> R13: 00000000006e0200 R14: 0000000000000000 R15: 0000000000000000
>
> Allocated by task 6821:
> save_stack mm/kasan/common.c:48 [inline]
> set_track mm/kasan/common.c:56 [inline]
> __kasan_kmalloc+0x103/0x140 mm/kasan/common.c:494
> kmem_cache_alloc_trace+0x234/0x300 mm/slab.c:3551
> kmalloc include/linux/slab.h:555 [inline]
> kzalloc include/linux/slab.h:669 [inline]
> hci_chan_create+0x9a/0x270 net/bluetooth/hci_conn.c:1692
> l2cap_conn_add+0x66/0xb00 net/bluetooth/l2cap_core.c:7699
> l2cap_connect_cfm+0xdb/0x12b0 net/bluetooth/l2cap_core.c:8097
> hci_connect_cfm include/net/bluetooth/hci_core.h:1340 [inline]
> hci_remote_features_evt net/bluetooth/hci_event.c:3210 [inline]
> hci_event_packet+0x1164c/0x18260 net/bluetooth/hci_event.c:6061
> hci_rx_work+0x236/0x9c0 net/bluetooth/hci_core.c:4705
> process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
> worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
> kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
>
> Freed by task 1530:
> save_stack mm/kasan/common.c:48 [inline]
> set_track mm/kasan/common.c:56 [inline]
> kasan_set_free_info mm/kasan/common.c:316 [inline]
> __kasan_slab_free+0x114/0x170 mm/kasan/common.c:455
> __cache_free mm/slab.c:3426 [inline]
> kfree+0x10a/0x220 mm/slab.c:3757
> hci_disconn_loglink_complete_evt net/bluetooth/hci_event.c:4999 [inline]
> hci_event_packet+0x304e/0x18260 net/bluetooth/hci_event.c:6188
> hci_rx_work+0x236/0x9c0 net/bluetooth/hci_core.c:4705
> process_one_work+0x789/0xfc0 kernel/workqueue.c:2269
> worker_thread+0xaa4/0x1460 kernel/workqueue.c:2415
> kthread+0x37e/0x3a0 drivers/block/aoe/aoecmd.c:1234
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293
>
> The buggy address belongs to the object at ffff8880a9591f00
> which belongs to the cache kmalloc-128 of size 128
> The buggy address is located 24 bytes inside of
> 128-byte region [ffff8880a9591f00, ffff8880a9591f80)
> The buggy address belongs to the page:
> page:ffffea0002a56440 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8880a9591800
> flags: 0xfffe0000000200(slab)
> raw: 00fffe0000000200 ffffea0002a5a648 ffffea00028a4a08 ffff8880aa400700
> raw: ffff8880a9591800 ffff8880a9591000 000000010000000a 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff8880a9591e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8880a9591e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> ffff8880a9591f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff8880a9591f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8880a9592000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at [email protected].
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
On Thu, Jun 03, 2021 at 11:30:08AM -0700, SyzScope wrote:
> Hi developers,
>
> Besides the control flow hijacking primitive we sent before, we managed to
> discover an additional double free primitive in this bug, making this bug
> even more dangerous.
>
> We created a web page with detailed descriptions: https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-hci_chan_del
>
> We understand that creating a patch can be time-consuming and there is
> probably a long list of bugs pending fixes. We hope that our security
> analysis can enable an informed decision on which bugs to fix first
> (prioritization).
>
> Since the bug has been on syzbot for over ten months (first found on
> 08-03-2020 and still can be triggered on 05-08-2021), it is best to have the
> bug fixed early enough to avoid it being weaponized.
Wonderful, please help out by sending a fix for this.
thanks,
greg k-h
On Tue, May 04, 2021 at 02:50:03PM -0700, ETenal wrote:
> Hi,
>
> This is SyzScope, a research project that aims to reveal high-risk
> primitives from a seemingly low-risk bug (UAF/OOB read, WARNING, BUG, etc.).
Who is working on and doing this "reseach project"? And what is it
doing to actually fix the issues that syzbot finds? Seems like that
would be a better solution instead of just trying to send emails saying,
in short "why isn't this reported issue fixed yet?"
thanks,
greg k-h
Hi Greg,
> I do not recall that, sorry, when was that?
We sent an email to [email protected] from [email protected] account on
May 20, the title is "KASAN: use-after-free Read in hci_chan_del has
dangerous security impact".
> Is that really the reason why syzbot-reported problems are not being
> fixed? Just because we don't know which ones are more "important"?
>
> As someone who has been managing many interns for a year or so working
> on these, I do not think that is the problem, but hey, what do I know...
Perhaps we misunderstood the problem of syzbot-generated bugs. Our
understanding is that if a syzbot-generated bug is exploited in the wild
and/or the exploit code is made publicly available somehow, then the bug
will be fixed in a prioritized fashion. If our understanding is correct,
wouldn't it be nice if we, as good guys, can figure out which bugs are
security-critical and patch them before the bad guys exploit them.
On 05/06/2021 00:43, Greg KH wrote:
> On Fri, Jun 04, 2021 at 10:11:03AM -0700, SyzScope wrote:
>> Hi Greg,
>>
>>> Who is working on and doing this "reseach project"?
>> We are a group of researchers from University of California, Riverside (we
>> introduced ourselves in an earlier email to [email protected] if you
>> recall).
> I do not recall that, sorry, when was that?
>
>> Please allow us to articulate the goal of our research. We'd be
>> happy to hear your feedback and suggestions.
>>
>>> And what is it
>>> doing to actually fix the issues that syzbot finds? Seems like that
>>> would be a better solution instead of just trying to send emails saying,
>>> in short "why isn't this reported issue fixed yet?"
>> From our limited understanding, we know a key problem with syzbot bugs is
>> that there are too many of them - more than what can be handled by
>> developers and maintainers. Therefore, it seems some form of prioritization
>> on bug fixing would be helpful. The goal of the SyzScope project is to
>> *automatically* analyze the security impact of syzbot bugs, which helps with
>> prioritizing bug fixes. In other words, when a syzbot bug is reported, we
>> aim to attach a corresponding security impact "signal" to help developers
>> make an informed decision on which ones to fix first.
> Is that really the reason why syzbot-reported problems are not being
> fixed? Just because we don't know which ones are more "important"?
>
> As someone who has been managing many interns for a year or so working
> on these, I do not think that is the problem, but hey, what do I know...
>
>> Currently, SyzScope is a standalone prototype system that we plan to open
>> source. We hope to keep developing it to make it more and more useful and
>> have it eventually integrated into syzbot (we are in talks with Dmitry).
>>
>> We are happy to talk more offline (perhaps even in a zoom meeting if you
>> would like). Thanks in advance for any feedback and suggestions you may
>> have.
> Meetings are not really how kernel development works, sorry.
>
> At the moment, these emails really do not seem all that useful, trying
> to tell other people what to do does not get you very far when dealing
> with people who you have no "authority" over...
>
> Technical solutions to human issues almost never work, however writing a
> procmail filter to keep me from having to see these will work quite well :)
>
> good luck!
>
> greg k-h
On Sat, Jun 05, 2021 at 09:43:43AM +0200, Greg KH wrote:
> On Fri, Jun 04, 2021 at 10:11:03AM -0700, SyzScope wrote:
> > Hi Greg,
> >
> > > Who is working on and doing this "reseach project"?
> > We are a group of researchers from University of California, Riverside (we
> > introduced ourselves in an earlier email to [email protected] if you
> > recall).
>
> I do not recall that, sorry, when was that?
>
> >?Please allow us to articulate the goal of our research. We'd be
> > happy to hear your feedback and suggestions.
> >
> > > And what is it
> > > doing to actually fix the issues that syzbot finds? Seems like that
> > > would be a better solution instead of just trying to send emails saying,
> > > in short "why isn't this reported issue fixed yet?"
> > From our limited understanding, we know a key problem with syzbot bugs is
> > that there are too many of them - more than what can be handled by
> > developers and maintainers. Therefore, it seems some form of prioritization
> > on bug fixing would be helpful. The goal of the SyzScope project is to
> > *automatically* analyze the security impact of syzbot bugs, which helps with
> > prioritizing bug fixes. In other words, when a syzbot bug is reported, we
> > aim to attach a corresponding security impact "signal" to help developers
> > make an informed decision on which ones to fix first.
>
> Is that really the reason why syzbot-reported problems are not being
> fixed? Just because we don't know which ones are more "important"?
>
> As someone who has been managing many interns for a year or so working
> on these, I do not think that is the problem, but hey, what do I know...
My 2 cents, as the one who is fixing these external and internal syzkaller bugs
in RDMA. I would say that the main reason is lack of specific knowledge to fix
them or/and amount of work to actually do it.
Many of such failures are in neglected parts of code.
And no, I personally won't care if someone adds security score or not to
syzkaller report, all reports should be fixed.
Thanks
On Sun, Jun 06, 2021 at 04:50:04PM +0800, Hillf Danton wrote:
> On 2020-08-02 20:45
> > syzbot found the following issue on:
> >
> > HEAD commit: ac3a0c84 Merge git://git.kernel.org/pub/scm/linux/kernel/g..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=11b8d570900000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=e59ee776d5aa8d55
> > dashboard link: https://syzkaller.appspot.com/bug?extid=305a91e025a73e4fd6ce
> > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11f7ceea900000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17e5de04900000
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: [email protected]
> >
> > IPVS: ftp: loaded support on port[0] = 21
> > ==================================================================
> > BUG: KASAN: use-after-free in hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
> > Read of size 8 at addr ffff8880a9591f18 by task syz-executor081/6793
> >
> > CPU: 0 PID: 6793 Comm: syz-executor081 Not tainted 5.8.0-rc7-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Call Trace:
> > __dump_stack lib/dump_stack.c:77 [inline]
> > dump_stack+0x1f0/0x31e lib/dump_stack.c:118
> > print_address_description+0x66/0x5a0 mm/kasan/report.c:383
> > __kasan_report mm/kasan/report.c:513 [inline]
> > kasan_report+0x132/0x1d0 mm/kasan/report.c:530
> > hci_chan_del+0x33/0x130 net/bluetooth/hci_conn.c:1707
> > l2cap_conn_del+0x4c2/0x650 net/bluetooth/l2cap_core.c:1900
> > hci_disconn_cfm include/net/bluetooth/hci_core.h:1355 [inline]
> > hci_conn_hash_flush+0x127/0x200 net/bluetooth/hci_conn.c:1536
> > hci_dev_do_close+0xb7b/0x1040 net/bluetooth/hci_core.c:1761
> > hci_unregister_dev+0x16d/0x1590 net/bluetooth/hci_core.c:3606
> > vhci_release+0x73/0xc0 drivers/bluetooth/hci_vhci.c:340
> > __fput+0x2f0/0x750 fs/file_table.c:281
> > task_work_run+0x137/0x1c0 kernel/task_work.c:135
> > exit_task_work include/linux/task_work.h:25 [inline]
> > do_exit+0x601/0x1f80 kernel/exit.c:805
> > do_group_exit+0x161/0x2d0 kernel/exit.c:903
> > __do_sys_exit_group+0x13/0x20 kernel/exit.c:914
> > __se_sys_exit_group+0x10/0x10 kernel/exit.c:912
> > __x64_sys_exit_group+0x37/0x40 kernel/exit.c:912
> > do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:384
> > entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> To fix the uaf reported, add reference count to hci channel to track users.
> Then only channels with zero users will be released.
>
> It is now only for thoughts.
>
> +++ x/include/net/bluetooth/hci_core.h
> @@ -704,6 +704,7 @@ struct hci_chan {
> struct sk_buff_head data_q;
> unsigned int sent;
> __u8 state;
> + atomic_t ref;
Please no, never use "raw" atomic variables. Especially for something
like this, use a kref.
thanks,
greg k-h
Hi SyzScope,
On Fri, May 28, 2021 at 02:12:01PM -0700, SyzScope wrote:
> The bug was reported by syzbot first in Aug 2020. Since it remains
> unpatched to this date, we have conducted some analysis to determine its
> security impact and root causes, which hopefully can help with the
> patching decisions.
> Specifically, we find that even though it is labeled as "UAF read" by
> syzbot, it can in fact lead to double free and control flow hijacking as
> well. Here is our analysis below (on this kernel version:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/?id=af5043c89a8ef6b6949a245fff355a552eaed240)
>
> ----------------------------- Root cause analysis:
> --------------------------
> The use-after-free bug happened because the object has two different
> references. But when it was freed, only one reference was removed,
> allowing the other reference to be used incorrectly.
> [...]
Thank you very much for your detailed analysis. I think this is very
valuable work, and I appreciate you doing it. I wanted to jump in to
this thread here so as not to discourage you, following Greg's hasty
dismissal. The bad arguments made I've seen have been something like:
- Who cares about the impact? Bugs are bugs and these should be fixed
regardless. Severity ratings are a waste of time.
- Spend your time writing patches, not writing tools to discover
security issues.
- This doesn't help my interns.
- "research project" scare quotes.
I think this entire set of argumentation is entirely bogus, and I really
hope it doesn't dissuade you from continuing to conduct useful research
on the kernel.
Specifically, it sounds like your tool is scanning through syzbot
reports, loading them into a symbolic execution engine, and seeing what
other primitives you can finesse out of the bugs, all in an automated
way. So, in the end, a developer gets a report that, rather than just
saying "4 byte out of bounds read into all zeroed memory so not a big
deal anyway even if it should be fixed," the developer gets a report
that says, "4 byte out of bounds read, or a UaF if approached in this
other way." Knowing that seems like very useful information, not just
for prioritization, but also for the urgency at which patches might be
deployed. For example, that's a meaningful distinction were that kind of
bug found in core networking stack or in wifi or ethernet drivers. I
also think it's great that you're pushing forward the field of automated
vulnerability discovery and exploit writing. Over time, hopefully that
leads to crushing all sorts of classes of bugs. It's also impressive
that you're able to do so much with kernel code in a symbolic execution
environment; this sounds a few steps beyond Angr ;-)...
My one suggestion would be that your email alerts / follow-ups to syzbot
reports, if automated, contain a bit more "dumbed-down" information
about what's happening. Not all kernel developers speak security, and as
you've seen, in some places it might be an uphill battle to have your
contributions taken seriously. On the other hand, it sounds like you
might already be working with Dmitry to integrate this into the
syzkaller infrastructure itself, somehow? If so, that'd be great.
Regards,
Jason
syzbot suspects this issue was fixed by commit:
commit 43016d02cf6e46edfc4696452251d34bba0c0435
Author: Florian Westphal <[email protected]>
Date: Mon May 3 11:51:15 2021 +0000
netfilter: arptables: use pernet ops struct during unregister
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1325d967d00000
start commit: af5043c8 Merge tag 'acpi-5.10-rc4' of git://git.kernel.org..
git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=f9aa2432c01bcb1f
dashboard link: https://syzkaller.appspot.com/bug?extid=305a91e025a73e4fd6ce
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=130152a1500000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=102b1bba500000
If the result looks correct, please mark the issue as fixed by replying with:
#syz fix: netfilter: arptables: use pernet ops struct during unregister
For information about bisection process see: https://goo.gl/tpsmEJ#bisection