Re: general protection fault in ebitmap_destroy

[Stephen Smalley]

On Wed, 2019-01-09 at 07:41 -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    a88cc8da0279 Merge branch 'akpm' (patches from
> Andrew)
> git tree:       upstream
> console output: 
> https://syzkaller.appspot.com/x/log.txt?x=1722da4f400000
> kernel config:  
> https://syzkaller.appspot.com/x/.config?x=edf1c3031097c304
> dashboard link: 
> https://syzkaller.appspot.com/bug?extid=6664500f0f18f07a5c0e
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro:      
> https://syzkaller.appspot.com/x/repro.syz?x=12d43580c00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the
> commit:
> Reported-by: syzbot+6664500f0f18f07a5c0e@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> SELinux: failed to load policy
> sel_write_load: 238 callbacks suppressed
> SELinux: failed to load policy
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 9316 Comm: syz-executor2 Not tainted 5.0.0-rc1+ #16
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS  
> Google 01/01/2011
> RIP: 0010:ebitmap_destroy+0x32/0xf0 security/selinux/ss/ebitmap.c:334
> Code: 49 89 fd 41 54 53 e8 9d e6 36 fe 4d 85 ed 0f 84 99 00 00 00 e8
> 8f e6  
> 36 fe 4c 89 ea 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c 02
> 00 0f  
> 85 98 00 00 00 49 be 00 00 00 00 00 fc ff df 4d 8b
> RSP: 0018:ffff88808967f5c0 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: ffff88808967f6a8 RCX: dffffc0000000000
> RDX: 0000000000000001 RSI: ffffffff834b1081 RDI: 0000000000000008
> RBP: ffff88808967f5e0 R08: ffff8880972a8140 R09: ffffed1015cc5b90
> R10: ffffed1015cc5b8f R11: ffff8880ae62dc7b R12: ffff888099d993c0
> R13: 0000000000000008 R14: ffff888099d993c0 R15: ffff88808967f648
> FS:  00007f70cd9e5700(0000) GS:ffff8880ae600000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000015e7938 CR3: 0000000096c4a000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   sens_destroy+0x49/0xa0 security/selinux/ss/policydb.c:735
>   sens_read+0x25d/0x460 security/selinux/ss/policydb.c:1636
>   policydb_read+0xed9/0x60d0 security/selinux/ss/policydb.c:2430
>   security_load_policy+0x423/0x1830
> security/selinux/ss/services.c:2129
>   sel_write_load+0x25a/0x470 security/selinux/selinuxfs.c:565
>   __vfs_write+0x116/0xb40 fs/read_write.c:485
>   vfs_write+0x20c/0x580 fs/read_write.c:549
>   ksys_write+0x105/0x260 fs/read_write.c:598
>   __do_sys_write fs/read_write.c:610 [inline]
>   __se_sys_write fs/read_write.c:607 [inline]
>   __x64_sys_write+0x73/0xb0 fs/read_write.c:607
>   do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x457ec9
> Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f70cd9e4c78 EFLAGS: 00000246 ORIG_RAX:
> 0000000000000001
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457ec9
> RDX: 000000000000005c RSI: 0000000020000000 RDI: 0000000000000003
> RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f70cd9e56d4
> R13: 00000000004c720f R14: 00000000004dc9a0 R15: 00000000ffffffff
> Modules linked in:
> ---[ end trace 78ea480790940b53 ]---
> RIP: 0010:ebitmap_destroy+0x32/0xf0 security/selinux/ss/ebitmap.c:334
> Code: 49 89 fd 41 54 53 e8 9d e6 36 fe 4d 85 ed 0f 84 99 00 00 00 e8
> 8f e6  
> 36 fe 4c 89 ea 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c 02
> 00 0f  
> 85 98 00 00 00 49 be 00 00 00 00 00 fc ff df 4d 8b
> RSP: 0018:ffff88808967f5c0 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: ffff88808967f6a8 RCX: dffffc0000000000
> RDX: 0000000000000001 RSI: ffffffff834b1081 RDI: 0000000000000008
> RBP: ffff88808967f5e0 R08: ffff8880972a8140 R09: ffffed1015cc5b90
> R10: ffffed1015cc5b8f R11: ffff8880ae62dc7b R12: ffff888099d993c0
> R13: 0000000000000008 R14: ffff888099d993c0 R15: ffff88808967f648
> FS:  00007f70cd9e5700(0000) GS:ffff8880ae700000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000073c000 CR3: 0000000096c4a000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Possible fix below