Message-ID: <022193b1-4ddd-f04e-aafa-ce249ec6d120@oracle.com>
Date:   Wed, 8 Dec 2021 11:29:47 -0500
From:   George Kennedy <george.kennedy@...cle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     davem@...emloft.net, kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tun: avoid double free in tun_free_netdev



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@...glegroups.com>
>> Signed-off-by: George Kennedy <george.kennedy@...cle.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

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