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SubjectKASAN: use-after-free Read in __rhashtable_lookup

syzbot found the following crash on:

HEAD commit: a394b3af206c ppp: mppe: Remove VLA usage
git tree: net-next
console output:
kernel config:
dashboard link:
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:

BUG: KASAN: use-after-free in memcmp+0xe8/0x150 lib/string.c:861
Read of size 1 at addr ffff8801d811ec30 by task syz-executor6/10904

CPU: 1 PID: 10904 Comm: syz-executor6 Not tainted 4.18.0-rc7+ #169
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+0x242/0x2fe mm/kasan/report.c:412
__asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:430
memcmp+0xe8/0x150 lib/string.c:861
memcmp include/linux/string.h:386 [inline]
rhashtable_compare include/linux/rhashtable.h:462 [inline]
rhashtable_lookup include/linux/rhashtable.h:516 [inline]
rhashtable_lookup_fast include/linux/rhashtable.h:542 [inline]
rds_add_bound net/rds/bind.c:117 [inline]
rds_bind+0x7c9/0x1510 net/rds/bind.c:238
__sys_bind+0x331/0x440 net/socket.c:1500
__do_sys_bind net/socket.c:1511 [inline]
__se_sys_bind net/socket.c:1509 [inline]
__x64_sys_bind+0x73/0xb0 net/socket.c:1509
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
RIP: 0033:0x456b29
Code: fd b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f6ae7f39c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 00007f6ae7f3a6d4 RCX: 0000000000456b29
RDX: 0000000000000010 RSI: 0000000020000840 RDI: 0000000000000014
RBP: 0000000000930140 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004ca698 R14: 00000000004c26f1 R15: 0000000000000001

Allocated by task 10898:
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
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
kmem_cache_alloc+0x12e/0x760 mm/slab.c:3554
sk_prot_alloc+0x69/0x2e0 net/core/sock.c:1462
sk_alloc+0x106/0x17b0 net/core/sock.c:1522
rds_create+0x14f/0x770 net/rds/af_rds.c:666
__sock_create+0x53c/0x940 net/socket.c:1294
sock_create net/socket.c:1334 [inline]
__sys_socket+0x106/0x260 net/socket.c:1364
__do_sys_socket net/socket.c:1373 [inline]
__se_sys_socket net/socket.c:1371 [inline]
__x64_sys_socket+0x73/0xb0 net/socket.c:1371
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290

Freed by task 10895:
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]
kmem_cache_free+0x86/0x2d0 mm/slab.c:3756
sk_prot_free net/core/sock.c:1503 [inline]
__sk_destruct+0x70a/0xa60 net/core/sock.c:1587
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]
rds_release+0x3e9/0x570 net/rds/af_rds.c:91
__sock_release+0xd7/0x250 net/socket.c:598
sock_close+0x19/0x20 net/socket.c:1158
__fput+0x355/0x8b0 fs/file_table.c:209
____fput+0x15/0x20 fs/file_table.c:243
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

The buggy address belongs to the object at ffff8801d811e7c0
which belongs to the cache RDS of size 1608
The buggy address is located 1136 bytes inside of
1608-byte region [ffff8801d811e7c0, ffff8801d811ee08)
The buggy address belongs to the page:
page:ffffea0007604780 count:1 mapcount:0 mapping:ffff8801cd8a0300 index:0x0
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffff8801cd89f348 ffffea000716f8c8 ffff8801cd8a0300
raw: 0000000000000000 ffff8801d811e0c0 0000000100000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801d811eb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d811eb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801d811ec00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d811ec80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801d811ed00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

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