On 08/20/2018 07:46 PM, Eric Biggers wrote:

On Wed, Aug 15, 2018 at 09:35:03AM -0700, syzbot wrote:

quoted

Hello,

syzbot found the following crash on:

HEAD commit:    5ed5da74de9e Add linux-next specific files for 20180813
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13fd82c4400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=18edf0289d1b5ab
dashboard link: https://syzkaller.appspot.com/bug?extid=94ee41ce442afe333d2e
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+94ee41ce442afe333d2e@syzkaller.appspotmail.com

RDX: 00000000200002c0 RSI: 0000000000000005 RDI: 0000000000000004
RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000f6a R11: 0000000000000246 R12: 0000000000000006
R13: 00000000004d3840 R14: 00000000004c85ae R15: 0000000000000003
==================================================================
BUG: KASAN: use-after-free in sha512_mb_flusher+0x572/0x610
arch/x86/crypto/sha512-mb/sha512_mb.c:940
Read of size 8 at addr ffff8801b35669d8 by task kworker/0:2/1879

CPU: 0 PID: 1879 Comm: kworker/0:2 Not tainted 4.18.0-next-20180813+ #37
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: crypto mcryptd_flusher
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
 print_address_description+0x6c/0x20b mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.7+0x242/0x30d mm/kasan/report.c:412
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
 sha512_mb_flusher+0x572/0x610 arch/x86/crypto/sha512-mb/sha512_mb.c:940
 mcryptd_flusher+0x342/0x4b0 crypto/mcryptd.c:208
 process_one_work+0xc73/0x1aa0 kernel/workqueue.c:2153
 worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
 kthread+0x35a/0x420 kernel/kthread.c:246
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415

Allocated by task 18983:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
 __do_kmalloc mm/slab.c:3718 [inline]
 __kmalloc+0x14e/0x720 mm/slab.c:3727
 kmalloc include/linux/slab.h:518 [inline]
 sock_kmalloc+0x156/0x1f0 net/core/sock.c:1983
 hash_accept_parent_nokey+0x58/0x2e0 crypto/algif_hash.c:438
 hash_accept_parent+0x5b/0x80 crypto/algif_hash.c:465
 af_alg_accept+0x127/0x7d0 crypto/af_alg.c:296
 alg_accept+0x46/0x60 crypto/af_alg.c:332
 __sys_accept4+0x3b2/0x8a0 net/socket.c:1589
 __do_sys_accept4 net/socket.c:1624 [inline]
 __se_sys_accept4 net/socket.c:1621 [inline]
 __x64_sys_accept4+0x97/0xf0 net/socket.c:1621
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 18979:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
 kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
 __cache_free mm/slab.c:3498 [inline]
 kfree+0xd9/0x210 mm/slab.c:3813
 __sock_kfree_s net/core/sock.c:2004 [inline]
 sock_kfree_s+0x29/0x60 net/core/sock.c:2010
 hash_sock_destruct+0x157/0x1c0 crypto/algif_hash.c:427
 __sk_destruct+0x107/0xa60 net/core/sock.c:1560
 sk_destruct+0x78/0x90 net/core/sock.c:1595
 __sk_free+0xcf/0x300 net/core/sock.c:1606
 sk_free+0x42/0x50 net/core/sock.c:1617
 sock_put include/net/sock.h:1691 [inline]
 af_alg_release+0x6e/0x90 crypto/af_alg.c:126
 __sock_release+0xd7/0x250 net/socket.c:580
 sock_close+0x19/0x20 net/socket.c:1140
 __fput+0x376/0x8a0 fs/file_table.c:279
 ____fput+0x15/0x20 fs/file_table.c:312
 task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:193 [inline]
 exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
 do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801b3566600
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 984 bytes inside of
 2048-byte region [ffff8801b3566600, ffff8801b3566e00)
The buggy address belongs to the page:
page:ffffea0006cd5980 count:1 mapcount:0 mapping:ffff8801dac00c40 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea0006cf2c08 ffffea000764ef08 ffff8801dac00c40
raw: 0000000000000000 ffff8801b3566600 0000000100000003 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801b3566880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b3566900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

quoted

ffff8801b3566980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

                                                    ^
 ffff8801b3566a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b3566a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

This is probably the same root cause as the other sha512_mb use-after-free
(https://lkml.org/lkml/2018/8/15/296), see my reply there.

#syz dup: KASAN: use-after-free Read in sha512_ctx_mgr_resubmit

- Eric

Yes, I think it is similar to the previous report.  Megha is working to debug
it.

Tim