[PATCH] tun: avoid double free in tun_free_netdev

[PATCH] tun: avoid double free in tun_free_netdev

[George Kennedy]

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 <syzkaller@googlegroups.com>
Signed-off-by: George Kennedy <george.kennedy@oracle.com>
---
 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

Re: [PATCH] tun: avoid double free in tun_free_netdev

[Greg KH]

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 <syzkaller@googlegroups.com>
> Signed-off-by: George Kennedy <george.kennedy@oracle.com>
> ---
>  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

Re: [PATCH] tun: avoid double free in tun_free_netdev

[George Kennedy]

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 <syzkaller@googlegroups.com>
>> Signed-off-by: George Kennedy <george.kennedy@oracle.com>
>> ---
>>   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

Re: [PATCH] tun: avoid double free in tun_free_netdev

[Greg KH]

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 <syzkaller@googlegroups.com>
> > > Signed-off-by: George Kennedy <george.kennedy@oracle.com>
> > > ---
> > >   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 <gregkh@linuxfoundation.org>

Re: [PATCH] tun: avoid double free in tun_free_netdev

[Stephen Hemminger]

On Wed, 8 Dec 2021 11:29:47 -0500
George Kennedy <george.kennedy@oracle.com> 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 <syzkaller@googlegroups.com>
> >> Signed-off-by: George Kennedy <george.kennedy@oracle.com>
> >> ---
> >>   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.

Re: [PATCH] tun: avoid double free in tun_free_netdev

[George Kennedy]

On 12/8/2021 11:36 AM, Stephen Hemminger wrote:
> On Wed, 8 Dec 2021 11:29:47 -0500
> George Kennedy <george.kennedy@oracle.com> 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 <syzkaller@googlegroups.com>
>>>> Signed-off-by: George Kennedy <george.kennedy@oracle.com>
>>>> ---
>>>>    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

Re: [PATCH] tun: avoid double free in tun_free_netdev

[Jakub Kicinski]

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.

Re: [PATCH] tun: avoid double free in tun_free_netdev

[George Kennedy]

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