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Date:   Thu, 07 Jun 2018 08:11:02 -0700
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Subject: Re: KASAN: slab-out-of-bounds Write in sha256_final
From:   syzbot <syzbot+8a608baf8751184ec727@syzkaller.appspotmail.com>
To:     davem@davemloft.net, herbert@gondor.apana.org.au,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com
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Sender: linux-kernel-owner@vger.kernel.org
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syzbot has found a reproducer for the following crash on:

HEAD commit:    1c8c5a9d38f6 Merge git://git.kernel.org/pub/scm/linux/kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12ed4ddf800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4f1acdf888c9d4e9
dashboard link: https://syzkaller.appspot.com/bug?extid=8a608baf8751184ec727
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=1338868f800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=115b474f800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8a608baf8751184ec727@syzkaller.appspotmail.com

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KASAN: slab-out-of-bounds in put_unaligned_be32  
include/linux/unaligned/access_ok.h:60 [inline]
BUG: KASAN: slab-out-of-bounds in sha256_base_finish  
include/crypto/sha256_base.h:124 [inline]
BUG: KASAN: slab-out-of-bounds in sha256_final+0x303/0x380  
crypto/sha256_generic.c:253
Write of size 4 at addr ffff8801d9167d60 by task syz-executor687/4515

CPU: 0 PID: 4515 Comm: syz-executor687 Not tainted 4.17.0+ #89
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1b9/0x294 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+0x242/0x2fe mm/kasan/report.c:412
  __asan_report_store4_noabort+0x17/0x20 mm/kasan/report.c:437
  put_unaligned_be32 include/linux/unaligned/access_ok.h:60 [inline]
  sha256_base_finish include/crypto/sha256_base.h:124 [inline]
  sha256_final+0x303/0x380 crypto/sha256_generic.c:253
  crypto_shash_final+0x104/0x260 crypto/shash.c:152
  kdf_ctr security/keys/dh.c:186 [inline]
  keyctl_dh_compute_kdf security/keys/dh.c:217 [inline]
  __keyctl_dh_compute+0x1184/0x1bc0 security/keys/dh.c:389
  keyctl_dh_compute+0xb9/0x100 security/keys/dh.c:425
  __do_sys_keyctl security/keys/keyctl.c:1741 [inline]
  __se_sys_keyctl security/keys/keyctl.c:1637 [inline]
  __x64_sys_keyctl+0x12a/0x3b0 security/keys/keyctl.c:1637
  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440019
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 6b 45 00 00 c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffdb8b0aca8 EFLAGS: 00000217 ORIG_RAX: 00000000000000fa
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440019
RDX: 0000000020000080 RSI: 00000000200001c0 RDI: 0000000000000017
RBP: 00000000006ca018 R08: 0000000020000200 R09: 00000000004002c8
R10: 0000000000000005 R11: 0000000000000217 R12: 0000000000401940
R13: 00000000004019d0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4515:
  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/0x760 mm/slab.c:3727
  kmalloc include/linux/slab.h:518 [inline]
  keyctl_dh_compute_kdf security/keys/dh.c:211 [inline]
  __keyctl_dh_compute+0xfe9/0x1bc0 security/keys/dh.c:389
  keyctl_dh_compute+0xb9/0x100 security/keys/dh.c:425
  __do_sys_keyctl security/keys/keyctl.c:1741 [inline]
  __se_sys_keyctl security/keys/keyctl.c:1637 [inline]
  __x64_sys_keyctl+0x12a/0x3b0 security/keys/keyctl.c:1637
  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 2870:
  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+0xd9/0x260 mm/slab.c:3813
  single_release+0x8f/0xb0 fs/seq_file.c:609
  __fput+0x353/0x890 fs/file_table.c:209
  ____fput+0x15/0x20 fs/file_table.c:243
  task_work_run+0x1e4/0x290 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:192 [inline]
  exit_to_usermode_loop+0x2bd/0x310 arch/x86/entry/common.c:166
  prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:265 [inline]
  do_syscall_64+0x6ac/0x800 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801d9167d40
  which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes to the right of
  32-byte region [ffff8801d9167d40, ffff8801d9167d60)
The buggy address belongs to the page:
page:ffffea00076459c0 count:1 mapcount:0 mapping:ffff8801d9167000  
index:0xffff8801d9167fc1
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801d9167000 ffff8801d9167fc1 0000000100000028
raw: ffffea00076581e0 ffffea0007646b20 ffff8801da8001c0 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801d9167c00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
  ffff8801d9167c80: 00 00 00 00 fc fc fc fc 00 00 00 00 fc fc fc fc
> ffff8801d9167d00: fb fb fb fb fc fc fc fc 00 00 00 00 fc fc fc fc
                                                        ^
  ffff8801d9167d80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
  ffff8801d9167e00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
==================================================================