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SubjectKASAN: slab-out-of-bounds Write in crypto_dh_encode_key
From
Hello,

syzbot found the following crash on:

HEAD commit: d00d6d9a339d Add linux-next specific files for 20180709
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10d146dc400000
kernel config: https://syzkaller.appspot.com/x/.config?x=94fe2b586beccacd
dashboard link: https://syzkaller.appspot.com/bug?extid=6d38d558c25b53b8f4ed
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=16af4f48400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14f562e0400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6d38d558c25b53b8f4ed@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 memcpy include/linux/string.h:345 [inline]
BUG: KASAN: slab-out-of-bounds in dh_pack_data crypto/dh_helper.c:21
[inline]
BUG: KASAN: slab-out-of-bounds in crypto_dh_encode_key+0x80e/0x830
crypto/dh_helper.c:60
Write of size 4 at addr ffff8801adbd6f10 by task syz-executor186/4466

CPU: 0 PID: 4466 Comm: syz-executor186 Not tainted
4.18.0-rc3-next-20180709+ #2
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+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_store_n_noabort+0x12/0x14 mm/kasan/report.c:449
memcpy include/linux/string.h:345 [inline]
dh_pack_data crypto/dh_helper.c:21 [inline]
crypto_dh_encode_key+0x80e/0x830 crypto/dh_helper.c:60
__keyctl_dh_compute+0x707/0x1c00 security/keys/dh.c:316
keyctl_dh_compute+0xc5/0x11f security/keys/dh.c:427
__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+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4403b9
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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcf524af58 EFLAGS: 00000213 ORIG_RAX: 00000000000000fa
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004403b9
RDX: 0000000020000540 RSI: 00000000200006c0 RDI: 0000000000000017
RBP: 00000000006ca018 R08: 0000000020c61fc8 R09: 00000000004002c8
R10: 0000000000000005 R11: 0000000000000213 R12: 0000000000401c40
R13: 0000000000401cd0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 4466:
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+0x6e1/0x1c00 security/keys/dh.c:311
keyctl_dh_compute+0xc5/0x11f security/keys/dh.c:427
__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+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 2899:
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:596
__fput+0x35d/0x930 fs/file_table.c:215
____fput+0x15/0x20 fs/file_table.c:251
task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:192 [inline]
exit_to_usermode_loop+0x313/0x370 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 ffff8801adbd6f00
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 16 bytes inside of
32-byte region [ffff8801adbd6f00, ffff8801adbd6f20)
The buggy address belongs to the page:
page:ffffea0006b6f580 count:1 mapcount:0 mapping:ffff8801da8001c0
index:0xffff8801adbd6fc1
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea00075c0288 ffffea00075c0388 ffff8801da8001c0
raw: ffff8801adbd6fc1 ffff8801adbd6000 000000010000003e 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801adbd6e00: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
ffff8801adbd6e80: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
> ffff8801adbd6f00: 00 00 03 fc fc fc fc fc 01 fc fc fc fc fc fc fc
^
ffff8801adbd6f80: 01 fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801adbd7000: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

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syzbot.
syzbot can test patches for this bug, for details see:
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