Re: BUG: unable to handle kernel NULL pointer dereference in __crypto_alg_lookup

[Stephan Mueller]

Am Montag, 18. Dezember 2017, 06:50:01 CET schrieb syzbot:

Hi,

> Hello,
> 
> syzkaller hit the following crash on
> 41d8c16909ebda40f7b4982a7f5e2ad102705ade
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
> 
> 
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
> IP: __crypto_alg_lookup+0x43/0x190 crypto/api.c:63
> PGD 0 P4D 0
> Oops: 0000 [#1] SMP
> Dumping ftrace buffer:
>     (ftrace buffer empty)
> Modules linked in:
> CPU: 1 PID: 3321 Comm: cryptomgr_probe Not tainted
> 4.15.0-rc3-next-20171213+ #66
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__crypto_alg_lookup+0x43/0x190 crypto/api.c:63
> RSP: 0018:ffffc900017ebd28 EFLAGS: 00010293
> RAX: ffff880216762080 RBX: 0000000000000000 RCX: ffffffff81673d23
> RDX: 0000000000000000 RSI: 0000000000000403 RDI: ffff880214eba120
> RBP: ffffc900017ebd70 R08: 0000000000000001 R09: 0000000000000001
> R10: ffffc900017ebcf0 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 000000000000240f R15: 0000000000000403
> FS:  0000000000000000(0000) GS:ffff88021fd00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000020 CR3: 000000020dc6b000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   crypto_alg_lookup+0x31/0x50 crypto/api.c:201
>   crypto_larval_lookup.part.8+0x34/0x1c0 crypto/api.c:218
>   crypto_larval_lookup crypto/api.c:212 [inline]
>   crypto_alg_mod_lookup+0x77/0x120 crypto/api.c:271
>   crypto_find_alg+0x63/0x70 crypto/api.c:501
>   crypto_grab_spawn+0x2f/0x80 crypto/algapi.c:631
>   crypto_grab_aead+0x35/0x40 crypto/aead.c:336
>   pcrypt_create_aead crypto/pcrypt.c:298 [inline]
>   pcrypt_create+0xca/0x2c0 crypto/pcrypt.c:346
>   cryptomgr_probe+0x40/0x100 crypto/algboss.c:75
>   kthread+0x149/0x170 kernel/kthread.c:238
>   ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
> Code: 89 7d d0 e8 70 66 c4 ff 48 8b 1d 59 e4 a6 01 48 81 fb 60 21 0e 83 0f
> 84 4c 01 00 00 c7 45 c4 fe ff ff ff 45 31 e4 e8 4d 66 c4 ff <44> 8b 6b 20
> 41 f6 c5 60 0f 85 03 01 00 00 e8 3a 66 c4 ff 44 89
> RIP: __crypto_alg_lookup+0x43/0x190 crypto/api.c:63 RSP: ffffc900017ebd28
> CR2: 0000000000000020
> ---[ end trace ff8e3661b9c3aa04 ]---
> Kernel panic - not syncing: Fatal exception
> Dumping ftrace buffer:
>     (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..

This bug seems to be triggerable again by the fact that some strange mask/type 
combo is used. When setting it to zero, there is no crash.

Therefore I would see that this issue would be covered with the fix that we 
currently work on to limit the number of allowed mask/type values.

Ciao
Stephan