Subject: KASAN: stack-out-of-bounds Read in rds_sendmsg

From: syzbot <bot+9461c9b9d340854a404b[email-masked]>
Date: Sat, 09 Dec 2017 02:41:00 -0800

Hello,

syzkaller hit the following crash on  
968edbd93c0cbb40ab48aca972392d377713a0c3
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.

syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers

==================================================================
BUG: KASAN: stack-out-of-bounds in rds_rdma_bytes net/rds/send.c:1013  
[inline]
BUG: KASAN: stack-out-of-bounds in rds_sendmsg+0x1f02/0x1f90  
net/rds/send.c:1066
Read of size 8 at addr ffff8801cbda7a60 by task syz-executor0/3092

CPU: 0 PID: 3092 Comm: syz-executor0 Not tainted 4.15.0-rc2+ #121
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x194/0x257 lib/dump_stack.c:53
  print_address_description+0x73/0x250 mm/kasan/report.c:252
  kasan_report_error mm/kasan/report.c:351 [inline]
  kasan_report+0x25b/0x340 mm/kasan/report.c:409
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
  rds_rdma_bytes net/rds/send.c:1013 [inline]
  rds_sendmsg+0x1f02/0x1f90 net/rds/send.c:1066
  sock_sendmsg_nosec net/socket.c:632 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:642
  ___sys_sendmsg+0x75b/0x8a0 net/socket.c:2048
  __sys_sendmsg+0xe5/0x210 net/socket.c:2082
  C_SYSC_sendmsg net/compat.c:739 [inline]
  compat_SyS_sendmsg+0x2a/0x40 net/compat.c:737
  do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
  do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
  entry_SYSENTER_compat+0x51/0x60 arch/x86/entry/entry_64_compat.S:125
RIP: 0023:0xf7f36c79
RSP: 002b:00000000ffdc503c EFLAGS: 00000292 ORIG_RAX: 0000000000000172
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000002048cfe4
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:000000007727554a count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: 0000000000000000 0000000100000001 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801cbda7900: 00 00 f2 f2 f2 f3 f3 f3 f3 00 00 00 00 00 00 00
  ffff8801cbda7980: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
> ffff8801cbda7a00: 00 f2 f2 f2 f2 f2 f2 f2 00 00 00 00 04 f2 f2 f2
                                                        ^
  ffff8801cbda7a80: f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 00 00 00
  ffff8801cbda7b00: 00 00 00 00 f2 f2 f2 f2 00 00 00 00 00 00 00 00
==================================================================

---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
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