Avoid double free in tun_free_netdev() by clearing tun->security
after free and using it to indicate that free has already been done.
BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
____kasan_slab_free mm/kasan/common.c:346 [inline]
__kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:1723 [inline]
slab_free_freelist_hook mm/slub.c:1749 [inline]
slab_free mm/slub.c:3513 [inline]
kfree+0xac/0x2d0 mm/slub.c:4561
selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
__tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
Reported-by: syzkaller <[email protected]>
Signed-off-by: George Kennedy <[email protected]>
---
drivers/net/tun.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 1572878..617c71f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
dev->tstats = NULL;
tun_flow_uninit(tun);
- security_tun_dev_free_security(tun->security);
+ if (tun->security) {
+ security_tun_dev_free_security(tun->security);
+ tun->security = NULL;
+ }
__tun_set_ebpf(tun, &tun->steering_prog, NULL);
__tun_set_ebpf(tun, &tun->filter_prog, NULL);
}
@@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
err_free_flow:
tun_flow_uninit(tun);
- security_tun_dev_free_security(tun->security);
+ if (tun->security) {
+ security_tun_dev_free_security(tun->security);
+ /* Let tun_free_netdev() know the free has already been done. */
+ tun->security = NULL;
+ }
err_free_stat:
free_percpu(dev->tstats);
err_free_dev:
--
1.8.3.1
On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:
> Avoid double free in tun_free_netdev() by clearing tun->security
> after free and using it to indicate that free has already been done.
>
> BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>
> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
> Hardware name: Red Hat KVM, BIOS
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
> print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
> kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
> ____kasan_slab_free mm/kasan/common.c:346 [inline]
> __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
> kasan_slab_free include/linux/kasan.h:235 [inline]
> slab_free_hook mm/slub.c:1723 [inline]
> slab_free_freelist_hook mm/slub.c:1749 [inline]
> slab_free mm/slub.c:3513 [inline]
> kfree+0xac/0x2d0 mm/slub.c:4561
> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
> tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
> netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
> rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
> __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:874 [inline]
> __se_sys_ioctl fs/ioctl.c:860 [inline]
> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Reported-by: syzkaller <[email protected]>
> Signed-off-by: George Kennedy <[email protected]>
> ---
> drivers/net/tun.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 1572878..617c71f 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
> dev->tstats = NULL;
>
> tun_flow_uninit(tun);
> - security_tun_dev_free_security(tun->security);
> + if (tun->security) {
> + security_tun_dev_free_security(tun->security);
> + tun->security = NULL;
> + }
> __tun_set_ebpf(tun, &tun->steering_prog, NULL);
> __tun_set_ebpf(tun, &tun->filter_prog, NULL);
> }
> @@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>
> err_free_flow:
> tun_flow_uninit(tun);
> - security_tun_dev_free_security(tun->security);
> + if (tun->security) {
> + security_tun_dev_free_security(tun->security);
> + /* Let tun_free_netdev() know the free has already been done. */
> + tun->security = NULL;
What protects this from racing with tun_free_netdev()?
And why can't security_tun_dev_free_security() handle a NULL value?
thanks,
greg k-h
On 12/8/2021 10:40 AM, Greg KH wrote:
> On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:
>> Avoid double free in tun_free_netdev() by clearing tun->security
>> after free and using it to indicate that free has already been done.
>>
>> BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>
>> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
>> Hardware name: Red Hat KVM, BIOS
>> Call Trace:
>> <TASK>
>> __dump_stack lib/dump_stack.c:88 [inline]
>> dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
>> print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
>> kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
>> ____kasan_slab_free mm/kasan/common.c:346 [inline]
>> __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
>> kasan_slab_free include/linux/kasan.h:235 [inline]
>> slab_free_hook mm/slub.c:1723 [inline]
>> slab_free_freelist_hook mm/slub.c:1749 [inline]
>> slab_free mm/slub.c:3513 [inline]
>> kfree+0xac/0x2d0 mm/slub.c:4561
>> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>> security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
>> tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
>> netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
>> rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
>> __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
>> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>> vfs_ioctl fs/ioctl.c:51 [inline]
>> __do_sys_ioctl fs/ioctl.c:874 [inline]
>> __se_sys_ioctl fs/ioctl.c:860 [inline]
>> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>> entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> Reported-by: syzkaller <[email protected]>
>> Signed-off-by: George Kennedy <[email protected]>
>> ---
>> drivers/net/tun.c | 11 +++++++++--
>> 1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index 1572878..617c71f 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
>> dev->tstats = NULL;
>>
>> tun_flow_uninit(tun);
>> - security_tun_dev_free_security(tun->security);
>> + if (tun->security) {
>> + security_tun_dev_free_security(tun->security);
>> + tun->security = NULL;
>> + }
>> __tun_set_ebpf(tun, &tun->steering_prog, NULL);
>> __tun_set_ebpf(tun, &tun->filter_prog, NULL);
>> }
>> @@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>>
>> err_free_flow:
>> tun_flow_uninit(tun);
>> - security_tun_dev_free_security(tun->security);
>> + if (tun->security) {
>> + security_tun_dev_free_security(tun->security);
>> + /* Let tun_free_netdev() know the free has already been done. */
>> + tun->security = NULL;
> What protects this from racing with tun_free_netdev()?
tun_free_netdev() is called after err_free_flow has already done the
free. rtnl_lock() and rtnl_unlock() prevent the race.
Here is the full KASAN report:
Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.
==================================================================
BUG: KASAN: double-free or invalid-free in
selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29
04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
____kasan_slab_free mm/kasan/common.c:346 [inline]
__kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:1723 [inline]
slab_free_freelist_hook mm/slub.c:1749 [inline]
slab_free mm/slub.c:3513 [inline]
kfree+0xac/0x2d0 mm/slub.c:4561
selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
__tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fd496f4c289
Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89
f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01
f0 ff ff 73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
</TASK>
Allocated by task 25750:
kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc mm/kasan/common.c:513 [inline]
__kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
kasan_kmalloc include/linux/kasan.h:269 [inline]
kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
kmalloc include/linux/slab.h:590 [inline]
kzalloc include/linux/slab.h:724 [inline]
selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
__tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
Freed by task 25750:
kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
kasan_set_track+0x25/0x30 mm/kasan/common.c:46
kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
____kasan_slab_free mm/kasan/common.c:366 [inline]
____kasan_slab_free mm/kasan/common.c:328 [inline]
__kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:1723 [inline]
slab_free_freelist_hook mm/slub.c:1749 [inline]
slab_free mm/slub.c:3513 [inline]
kfree+0xac/0x2d0 mm/slub.c:4561
selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
__tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
The buggy address belongs to the object at ffff888066b87370
which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
8-byte region [ffff888066b87370, ffff888066b87378)
The buggy address belongs to the page:
page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000
index:0x0 pfn:0x66b87
flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa
>ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc
^
ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
==================================================================
>
> And why can't security_tun_dev_free_security() handle a NULL value?
security_tun_dev_free_security() could be modified to handle the NULL value.
George
>
> thanks,
>
> greg k-h
On Wed, Dec 08, 2021 at 11:29:47AM -0500, George Kennedy wrote:
>
>
> On 12/8/2021 10:40 AM, Greg KH wrote:
> > On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:
> > > Avoid double free in tun_free_netdev() by clearing tun->security
> > > after free and using it to indicate that free has already been done.
> > >
> > > BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> > >
> > > CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
> > > Hardware name: Red Hat KVM, BIOS
> > > Call Trace:
> > > <TASK>
> > > __dump_stack lib/dump_stack.c:88 [inline]
> > > dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
> > > print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
> > > kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
> > > ____kasan_slab_free mm/kasan/common.c:346 [inline]
> > > __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
> > > kasan_slab_free include/linux/kasan.h:235 [inline]
> > > slab_free_hook mm/slub.c:1723 [inline]
> > > slab_free_freelist_hook mm/slub.c:1749 [inline]
> > > slab_free mm/slub.c:3513 [inline]
> > > kfree+0xac/0x2d0 mm/slub.c:4561
> > > selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> > > security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
> > > tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
> > > netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
> > > rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
> > > __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
> > > tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> > > vfs_ioctl fs/ioctl.c:51 [inline]
> > > __do_sys_ioctl fs/ioctl.c:874 [inline]
> > > __se_sys_ioctl fs/ioctl.c:860 [inline]
> > > __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> > > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > > do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> > > entry_SYSCALL_64_after_hwframe+0x44/0xae
> > >
> > > Reported-by: syzkaller <[email protected]>
> > > Signed-off-by: George Kennedy <[email protected]>
> > > ---
> > > drivers/net/tun.c | 11 +++++++++--
> > > 1 file changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> > > index 1572878..617c71f 100644
> > > --- a/drivers/net/tun.c
> > > +++ b/drivers/net/tun.c
> > > @@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
> > > dev->tstats = NULL;
> > > tun_flow_uninit(tun);
> > > - security_tun_dev_free_security(tun->security);
> > > + if (tun->security) {
> > > + security_tun_dev_free_security(tun->security);
> > > + tun->security = NULL;
> > > + }
> > > __tun_set_ebpf(tun, &tun->steering_prog, NULL);
> > > __tun_set_ebpf(tun, &tun->filter_prog, NULL);
> > > }
> > > @@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
> > > err_free_flow:
> > > tun_flow_uninit(tun);
> > > - security_tun_dev_free_security(tun->security);
> > > + if (tun->security) {
> > > + security_tun_dev_free_security(tun->security);
> > > + /* Let tun_free_netdev() know the free has already been done. */
> > > + tun->security = NULL;
> > What protects this from racing with tun_free_netdev()?
> tun_free_netdev() is called after err_free_flow has already done the free.
> rtnl_lock() and rtnl_unlock() prevent the race.
Ok, good, it wasn't obvious from the context here.
>
> Here is the full KASAN report:
>
> Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.
>
> ==================================================================
> BUG: KASAN: double-free or invalid-free in
> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>
> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
> Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29
> 04/01/2014
> Call Trace:
> ?<TASK>
> ?__dump_stack lib/dump_stack.c:88 [inline]
> ?dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
> ?print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
> ?kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
> ?____kasan_slab_free mm/kasan/common.c:346 [inline]
> ?__kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
> ?kasan_slab_free include/linux/kasan.h:235 [inline]
> ?slab_free_hook mm/slub.c:1723 [inline]
> ?slab_free_freelist_hook mm/slub.c:1749 [inline]
> ?slab_free mm/slub.c:3513 [inline]
> ?kfree+0xac/0x2d0 mm/slub.c:4561
> ?selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> ?security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
> ?tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
> ?netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
> ?rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
> ?__tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
> ?tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> ?vfs_ioctl fs/ioctl.c:51 [inline]
> ?__do_sys_ioctl fs/ioctl.c:874 [inline]
> ?__se_sys_ioctl fs/ioctl.c:860 [inline]
> ?__x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> ?do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> ?do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> ?entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7fd496f4c289
> Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89 f7
> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff
> 73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
> RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
> RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
> RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
> R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
> ?</TASK>
>
> Allocated by task 25750:
> ?kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
> ?kasan_set_track mm/kasan/common.c:46 [inline]
> ?set_alloc_info mm/kasan/common.c:434 [inline]
> ?____kasan_kmalloc mm/kasan/common.c:513 [inline]
> ?__kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
> ?kasan_kmalloc include/linux/kasan.h:269 [inline]
> ?kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
> ?kmalloc include/linux/slab.h:590 [inline]
> ?kzalloc include/linux/slab.h:724 [inline]
> ?selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
> ?security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
> ?tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
> ?__tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
> ?tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> ?vfs_ioctl fs/ioctl.c:51 [inline]
> ?__do_sys_ioctl fs/ioctl.c:874 [inline]
> ?__se_sys_ioctl fs/ioctl.c:860 [inline]
> ?__x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> ?do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> ?do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> ?entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Freed by task 25750:
> ?kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
> ?kasan_set_track+0x25/0x30 mm/kasan/common.c:46
> ?kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
> ?____kasan_slab_free mm/kasan/common.c:366 [inline]
> ?____kasan_slab_free mm/kasan/common.c:328 [inline]
> ?__kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
> ?kasan_slab_free include/linux/kasan.h:235 [inline]
> ?slab_free_hook mm/slub.c:1723 [inline]
> ?slab_free_freelist_hook mm/slub.c:1749 [inline]
> ?slab_free mm/slub.c:3513 [inline]
> ?kfree+0xac/0x2d0 mm/slub.c:4561
> ?selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> ?security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
> ?tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
> ?__tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
> ?tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> ?vfs_ioctl fs/ioctl.c:51 [inline]
> ?__do_sys_ioctl fs/ioctl.c:874 [inline]
> ?__se_sys_ioctl fs/ioctl.c:860 [inline]
> ?__x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> ?do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> ?do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> ?entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The buggy address belongs to the object at ffff888066b87370
> ?which belongs to the cache kmalloc-8 of size 8
> The buggy address is located 0 bytes inside of
> ?8-byte region [ffff888066b87370, ffff888066b87378)
> The buggy address belongs to the page:
> page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000
> index:0x0 pfn:0x66b87
> flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
> raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
> raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ?ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
> ?ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa
> >ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc
> ???????????????????????????????????????????????????????????? ^
> ?ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
> ?ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
> ==================================================================
>
> >
> > And why can't security_tun_dev_free_security() handle a NULL value?
>
> security_tun_dev_free_security() could be modified to handle the NULL value.
That's fine, most of this patch would still be needed even if you do
that.
Reviewed-by: Greg Kroah-Hartman <[email protected]>
On Wed, 8 Dec 2021 11:29:47 -0500
George Kennedy <[email protected]> wrote:
> On 12/8/2021 10:40 AM, Greg KH wrote:
> > On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:
> >> Avoid double free in tun_free_netdev() by clearing tun->security
> >> after free and using it to indicate that free has already been done.
> >>
> >> BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> >>
> >> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
> >> Hardware name: Red Hat KVM, BIOS
> >> Call Trace:
> >> <TASK>
> >> __dump_stack lib/dump_stack.c:88 [inline]
> >> dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
> >> print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
> >> kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
> >> ____kasan_slab_free mm/kasan/common.c:346 [inline]
> >> __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
> >> kasan_slab_free include/linux/kasan.h:235 [inline]
> >> slab_free_hook mm/slub.c:1723 [inline]
> >> slab_free_freelist_hook mm/slub.c:1749 [inline]
> >> slab_free mm/slub.c:3513 [inline]
> >> kfree+0xac/0x2d0 mm/slub.c:4561
> >> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> >> security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
> >> tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
> >> netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
> >> rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
> >> __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
> >> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> >> vfs_ioctl fs/ioctl.c:51 [inline]
> >> __do_sys_ioctl fs/ioctl.c:874 [inline]
> >> __se_sys_ioctl fs/ioctl.c:860 [inline]
> >> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> >> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> >> entry_SYSCALL_64_after_hwframe+0x44/0xae
> >>
> >> Reported-by: syzkaller <[email protected]>
> >> Signed-off-by: George Kennedy <[email protected]>
> >> ---
> >> drivers/net/tun.c | 11 +++++++++--
> >> 1 file changed, 9 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> >> index 1572878..617c71f 100644
> >> --- a/drivers/net/tun.c
> >> +++ b/drivers/net/tun.c
> >> @@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
> >> dev->tstats = NULL;
> >>
> >> tun_flow_uninit(tun);
> >> - security_tun_dev_free_security(tun->security);
> >> + if (tun->security) {
> >> + security_tun_dev_free_security(tun->security);
> >> + tun->security = NULL;
> >> + }
> >> __tun_set_ebpf(tun, &tun->steering_prog, NULL);
> >> __tun_set_ebpf(tun, &tun->filter_prog, NULL);
> >> }
> >> @@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
> >>
> >> err_free_flow:
> >> tun_flow_uninit(tun);
> >> - security_tun_dev_free_security(tun->security);
> >> + if (tun->security) {
> >> + security_tun_dev_free_security(tun->security);
> >> + /* Let tun_free_netdev() know the free has already been done. */
> >> + tun->security = NULL;
> > What protects this from racing with tun_free_netdev()?
> tun_free_netdev() is called after err_free_flow has already done the
> free. rtnl_lock() and rtnl_unlock() prevent the race.
>
> Here is the full KASAN report:
>
> Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.
>
> ==================================================================
> BUG: KASAN: double-free or invalid-free in
> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>
> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
> Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29
> 04/01/2014
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
> print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
> kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
> ____kasan_slab_free mm/kasan/common.c:346 [inline]
> __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
> kasan_slab_free include/linux/kasan.h:235 [inline]
> slab_free_hook mm/slub.c:1723 [inline]
> slab_free_freelist_hook mm/slub.c:1749 [inline]
> slab_free mm/slub.c:3513 [inline]
> kfree+0xac/0x2d0 mm/slub.c:4561
> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
> tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
> netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
> rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
> __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:874 [inline]
> __se_sys_ioctl fs/ioctl.c:860 [inline]
> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
> RIP: 0033:0x7fd496f4c289
> Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89
> f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01
> f0 ff ff 73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
> RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
> RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
> RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
> R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
> </TASK>
>
> Allocated by task 25750:
> kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
> kasan_set_track mm/kasan/common.c:46 [inline]
> set_alloc_info mm/kasan/common.c:434 [inline]
> ____kasan_kmalloc mm/kasan/common.c:513 [inline]
> __kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
> kasan_kmalloc include/linux/kasan.h:269 [inline]
> kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
> kmalloc include/linux/slab.h:590 [inline]
> kzalloc include/linux/slab.h:724 [inline]
> selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
> security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
> tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
> __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:874 [inline]
> __se_sys_ioctl fs/ioctl.c:860 [inline]
> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Freed by task 25750:
> kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
> kasan_set_track+0x25/0x30 mm/kasan/common.c:46
> kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
> ____kasan_slab_free mm/kasan/common.c:366 [inline]
> ____kasan_slab_free mm/kasan/common.c:328 [inline]
> __kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
> kasan_slab_free include/linux/kasan.h:235 [inline]
> slab_free_hook mm/slub.c:1723 [inline]
> slab_free_freelist_hook mm/slub.c:1749 [inline]
> slab_free mm/slub.c:3513 [inline]
> kfree+0xac/0x2d0 mm/slub.c:4561
> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
> security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
> tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
> __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:874 [inline]
> __se_sys_ioctl fs/ioctl.c:860 [inline]
> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The buggy address belongs to the object at ffff888066b87370
> which belongs to the cache kmalloc-8 of size 8
> The buggy address is located 0 bytes inside of
> 8-byte region [ffff888066b87370, ffff888066b87378)
> The buggy address belongs to the page:
> page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000
> index:0x0 pfn:0x66b87
> flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
> raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
> raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
> ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa
> >ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc
> ^
> ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
> ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
> ==================================================================
>
> >
> > And why can't security_tun_dev_free_security() handle a NULL value?
>
> security_tun_dev_free_security() could be modified to handle the NULL value.
It looks like a lot of the problem is duplicate unwind.
Why does err_free_flow, err_free_stat etc unwinds need to exist if
the free_netdev is going to do same thing.
On 12/8/2021 11:36 AM, Stephen Hemminger wrote:
> On Wed, 8 Dec 2021 11:29:47 -0500
> George Kennedy <[email protected]> wrote:
>
>> On 12/8/2021 10:40 AM, Greg KH wrote:
>>> On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote:
>>>> Avoid double free in tun_free_netdev() by clearing tun->security
>>>> after free and using it to indicate that free has already been done.
>>>>
>>>> BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>>>
>>>> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
>>>> Hardware name: Red Hat KVM, BIOS
>>>> Call Trace:
>>>> <TASK>
>>>> __dump_stack lib/dump_stack.c:88 [inline]
>>>> dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
>>>> print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
>>>> kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
>>>> ____kasan_slab_free mm/kasan/common.c:346 [inline]
>>>> __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
>>>> kasan_slab_free include/linux/kasan.h:235 [inline]
>>>> slab_free_hook mm/slub.c:1723 [inline]
>>>> slab_free_freelist_hook mm/slub.c:1749 [inline]
>>>> slab_free mm/slub.c:3513 [inline]
>>>> kfree+0xac/0x2d0 mm/slub.c:4561
>>>> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>>> security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
>>>> tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
>>>> netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
>>>> rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
>>>> __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
>>>> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>>>> vfs_ioctl fs/ioctl.c:51 [inline]
>>>> __do_sys_ioctl fs/ioctl.c:874 [inline]
>>>> __se_sys_ioctl fs/ioctl.c:860 [inline]
>>>> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>>>> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>>> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>>>> entry_SYSCALL_64_after_hwframe+0x44/0xae
>>>>
>>>> Reported-by: syzkaller <[email protected]>
>>>> Signed-off-by: George Kennedy <[email protected]>
>>>> ---
>>>> drivers/net/tun.c | 11 +++++++++--
>>>> 1 file changed, 9 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>>>> index 1572878..617c71f 100644
>>>> --- a/drivers/net/tun.c
>>>> +++ b/drivers/net/tun.c
>>>> @@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev)
>>>> dev->tstats = NULL;
>>>>
>>>> tun_flow_uninit(tun);
>>>> - security_tun_dev_free_security(tun->security);
>>>> + if (tun->security) {
>>>> + security_tun_dev_free_security(tun->security);
>>>> + tun->security = NULL;
>>>> + }
>>>> __tun_set_ebpf(tun, &tun->steering_prog, NULL);
>>>> __tun_set_ebpf(tun, &tun->filter_prog, NULL);
>>>> }
>>>> @@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
>>>>
>>>> err_free_flow:
>>>> tun_flow_uninit(tun);
>>>> - security_tun_dev_free_security(tun->security);
>>>> + if (tun->security) {
>>>> + security_tun_dev_free_security(tun->security);
>>>> + /* Let tun_free_netdev() know the free has already been done. */
>>>> + tun->security = NULL;
>>> What protects this from racing with tun_free_netdev()?
>> tun_free_netdev() is called after err_free_flow has already done the
>> free. rtnl_lock() and rtnl_unlock() prevent the race.
>>
>> Here is the full KASAN report:
>>
>> Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug.
>>
>> ==================================================================
>> BUG: KASAN: double-free or invalid-free in
>> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>>
>> CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1
>> Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7860+a7792d29
>> 04/01/2014
>> Call Trace:
>> <TASK>
>> __dump_stack lib/dump_stack.c:88 [inline]
>> dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106
>> print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247
>> kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372
>> ____kasan_slab_free mm/kasan/common.c:346 [inline]
>> __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374
>> kasan_slab_free include/linux/kasan.h:235 [inline]
>> slab_free_hook mm/slub.c:1723 [inline]
>> slab_free_freelist_hook mm/slub.c:1749 [inline]
>> slab_free mm/slub.c:3513 [inline]
>> kfree+0xac/0x2d0 mm/slub.c:4561
>> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>> security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
>> tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215
>> netdev_run_todo+0x4df/0x840 net/core/dev.c:10627
>> rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112
>> __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302
>> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>> vfs_ioctl fs/ioctl.c:51 [inline]
>> __do_sys_ioctl fs/ioctl.c:874 [inline]
>> __se_sys_ioctl fs/ioctl.c:860 [inline]
>> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>> entry_SYSCALL_64_after_hwframe+0x44/0xae
>> RIP: 0033:0x7fd496f4c289
>> Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89
>> f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01
>> f0 ff ff 73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48
>> RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289
>> RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003
>> RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c
>> R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700
>> </TASK>
>>
>> Allocated by task 25750:
>> kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
>> kasan_set_track mm/kasan/common.c:46 [inline]
>> set_alloc_info mm/kasan/common.c:434 [inline]
>> ____kasan_kmalloc mm/kasan/common.c:513 [inline]
>> __kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522
>> kasan_kmalloc include/linux/kasan.h:269 [inline]
>> kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261
>> kmalloc include/linux/slab.h:590 [inline]
>> kzalloc include/linux/slab.h:724 [inline]
>> selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594
>> security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336
>> tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727
>> __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
>> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>> vfs_ioctl fs/ioctl.c:51 [inline]
>> __do_sys_ioctl fs/ioctl.c:874 [inline]
>> __se_sys_ioctl fs/ioctl.c:860 [inline]
>> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>> entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> Freed by task 25750:
>> kasan_save_stack+0x26/0x60 mm/kasan/common.c:38
>> kasan_set_track+0x25/0x30 mm/kasan/common.c:46
>> kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370
>> ____kasan_slab_free mm/kasan/common.c:366 [inline]
>> ____kasan_slab_free mm/kasan/common.c:328 [inline]
>> __kasan_slab_free+0xe8/0x120 mm/kasan/common.c:374
>> kasan_slab_free include/linux/kasan.h:235 [inline]
>> slab_free_hook mm/slub.c:1723 [inline]
>> slab_free_freelist_hook mm/slub.c:1749 [inline]
>> slab_free mm/slub.c:3513 [inline]
>> kfree+0xac/0x2d0 mm/slub.c:4561
>> selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605
>> security_tun_dev_free_security+0x4f/0x90 security/security.c:2342
>> tun_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782
>> __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026
>> tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311
>> vfs_ioctl fs/ioctl.c:51 [inline]
>> __do_sys_ioctl fs/ioctl.c:874 [inline]
>> __se_sys_ioctl fs/ioctl.c:860 [inline]
>> __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860
>> do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>> do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80
>> entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> The buggy address belongs to the object at ffff888066b87370
>> which belongs to the cache kmalloc-8 of size 8
>> The buggy address is located 0 bytes inside of
>> 8-byte region [ffff888066b87370, ffff888066b87378)
>> The buggy address belongs to the page:
>> page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000
>> index:0x0 pfn:0x66b87
>> flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff)
>> raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280
>> raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>> ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc
>> ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa
>> >ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc
>> ^
>> ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc
>> ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc
>> ==================================================================
>>
>>> And why can't security_tun_dev_free_security() handle a NULL value?
>> security_tun_dev_free_security() could be modified to handle the NULL value.
> It looks like a lot of the problem is duplicate unwind.
> Why does err_free_flow, err_free_stat etc unwinds need to exist if
> the free_netdev is going to do same thing.
Maybe instead do not call security_tun_dev_free_security(tun->security)
in err_free_flow if it's going to be done anyway in tun_free_netdev().
George
On Wed, 8 Dec 2021 11:44:02 -0500 George Kennedy wrote:
> > It looks like a lot of the problem is duplicate unwind.
> > Why does err_free_flow, err_free_stat etc unwinds need to exist if
> > the free_netdev is going to do same thing.
>
> Maybe instead do not call security_tun_dev_free_security(tun->security)
> in err_free_flow if it's going to be done anyway in tun_free_netdev().
That won't be good either. register_netdevice() has multiple failure
modes, it may or may not call the destructor depending on where it
fails. Either the stuff that destructor undoes needs to be moved to
ndo_init (which is what destructor always pairs with), or you can check
dev->reg_state. If dev->reg_state is NETREG_UNREGISTERING that means
the destructor will be caller later.
The ndo_init way is preferable, just cut and past the appropriate lines
preceding registration into a ndo_init callback.
On 12/8/2021 6:58 PM, Jakub Kicinski wrote:
> On Wed, 8 Dec 2021 11:44:02 -0500 George Kennedy wrote:
>>> It looks like a lot of the problem is duplicate unwind.
>>> Why does err_free_flow, err_free_stat etc unwinds need to exist if
>>> the free_netdev is going to do same thing.
>> Maybe instead do not call security_tun_dev_free_security(tun->security)
>> in err_free_flow if it's going to be done anyway in tun_free_netdev().
> That won't be good either. register_netdevice() has multiple failure
> modes, it may or may not call the destructor depending on where it
> fails. Either the stuff that destructor undoes needs to be moved to
> ndo_init (which is what destructor always pairs with), or you can check
> dev->reg_state. If dev->reg_state is NETREG_UNREGISTERING that means
> the destructor will be caller later.
>
> The ndo_init way is preferable, just cut and past the appropriate lines
> preceding registration into a ndo_init callback.
Thank you Jakub,
Looking at other ndo_init's to try and figure out how much before
register_netdevice() should go in it.
George