Hello,
syzbot found the following crash on:
HEAD commit: a16afaf7928b Merge tag 'for-v4.18' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1338f6bf800000
kernel config: https://syzkaller.appspot.com/x/.config?x=314f2150f36c16ca
dashboard link: https://syzkaller.appspot.com/bug?extid=d2d729bdde65dee3eae6
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1173381f800000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=171f90cf800000
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email protected]
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KASAN: slab-out-of-bounds in bpf_skb_proto_xlat net/core/filter.c:2637
[inline]
BUG: KASAN: slab-out-of-bounds in ____bpf_skb_change_proto
net/core/filter.c:2675 [inline]
BUG: KASAN: slab-out-of-bounds in bpf_skb_change_proto+0xe37/0x1300
net/core/filter.c:2650
Read of size 2 at addr ffff8801b04646c0 by task syz-executor241/4519
CPU: 0 PID: 4519 Comm: syz-executor241 Not tainted 4.17.0+ #93
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+0x1b9/0x294 lib/dump_stack.c:113
print_address_description+0x6c/0x20b mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
__asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:431
bpf_skb_proto_xlat net/core/filter.c:2637 [inline]
____bpf_skb_change_proto net/core/filter.c:2675 [inline]
bpf_skb_change_proto+0xe37/0x1300 net/core/filter.c:2650
Allocated by task 0:
(stack is not available)
Freed by task 0:
(stack is not available)
The buggy address belongs to the object at ffff8801b04646c0
which belongs to the cache skbuff_head_cache of size 232
The buggy address is located 0 bytes inside of
232-byte region [ffff8801b04646c0, ffff8801b04647a8)
The buggy address belongs to the page:
page:ffffea0006c11900 count:1 mapcount:0 mapping:ffff8801d9a0d080 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea0006c49388 ffffea0006ae5c48 ffff8801d9a0d080
raw: 0000000000000000 ffff8801b0464080 000000010000000c 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff8801b0464580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801b0464600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801b0464680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8801b0464700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801b0464780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================
---
This bug is generated by a bot. It may contain errors.
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On 06/10/2018 05:27 PM, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: a16afaf7928b Merge tag 'for-v4.18' of git://git.kernel.org..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1338f6bf800000
> kernel config: https://syzkaller.appspot.com/x/.config?x=314f2150f36c16ca
> dashboard link: https://syzkaller.appspot.com/bug?extid=d2d729bdde65dee3eae6
> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1173381f800000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=171f90cf800000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: [email protected]
#syz fix: bpf: reject passing modified ctx to helper functions
On Mon, Jun 11, 2018 at 11:42 AM, Daniel Borkmann <[email protected]> wrote:
> On 06/10/2018 05:27 PM, syzbot wrote:
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit: a16afaf7928b Merge tag 'for-v4.18' of git://git.kernel.org..
>> git tree: upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=1338f6bf800000
>> kernel config: https://syzkaller.appspot.com/x/.config?x=314f2150f36c16ca
>> dashboard link: https://syzkaller.appspot.com/bug?extid=d2d729bdde65dee3eae6
>> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1173381f800000
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=171f90cf800000
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: [email protected]
>
> #syz fix: bpf: reject passing modified ctx to helper functions
On a related note, it seems that it still can unwind past
bpf_skb_change_proto. I think the "net.core.bpf_jit_kallsyms = 1"
sysctl should have been reached syzbot by the time of crash. Are you
sure that's the only thing requires? We are using frame pointer
unwinder just in case.
On 06/11/2018 11:52 AM, Dmitry Vyukov wrote:
> On Mon, Jun 11, 2018 at 11:42 AM, Daniel Borkmann <[email protected]> wrote:
>> On 06/10/2018 05:27 PM, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit: a16afaf7928b Merge tag 'for-v4.18' of git://git.kernel.org..
>>> git tree: upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1338f6bf800000
>>> kernel config: https://syzkaller.appspot.com/x/.config?x=314f2150f36c16ca
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=d2d729bdde65dee3eae6
>>> compiler: gcc (GCC) 8.0.1 20180413 (experimental)
>>> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1173381f800000
>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=171f90cf800000
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: [email protected]
>>
>> #syz fix: bpf: reject passing modified ctx to helper functions
>
> On a related note, it seems that it still can unwind past
> bpf_skb_change_proto. I think the "net.core.bpf_jit_kallsyms = 1"
> sysctl should have been reached syzbot by the time of crash. Are you
> sure that's the only thing requires? We are using frame pointer
> unwinder just in case.
Nah, I know what happened; just sent a PR fix for syzkaller.
Thanks,
Daniel