BUG: unable to handle kernel NULL pointer dereference in __crypto_alg_lookup

[syzbot]

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..


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[Stephan Mueller]

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

Hi,

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

[Eric Biggers]

AF_ALG definitely should be locked down more, but we should fix the bugs before
they get hidden; after all, they are likely reachable in other ways as well.
There is a bug in pcrypt which seems to be causing some of these reports. I've
sent out a fix and will mark the reports as a duplicate of the first:

#syz dup: KASAN: use-after-free Read in __list_del_entry_valid (2)

(It's a bit messy because the bug is causing a bogus pointer to be kfree()'d,
which can result in different symptoms, especially with slab merging.)