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Date:   Mon, 20 Aug 2018 19:46:16 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     syzbot <syzbot+94ee41ce442afe333d2e@...kaller.appspotmail.com>
Cc:     davem@...emloft.net, herbert@...dor.apana.org.au, hpa@...or.com,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        megha.dey@...ux.intel.com, mingo@...hat.com,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
        tim.c.chen@...ux.intel.com, x86@...nel.org
Subject: Re: KASAN: use-after-free Read in sha512_mb_flusher

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

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