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

From: syzbot <[email-masked]>
Date: Thu, 21 Dec 2017 01:10:00 -0800

syzkaller has found reproducer for the following crash on  
8f36e00065436412a02d1f50ad77375bdb506300
git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers

audit: type=1400 audit(1513847224.110:7): avc:  denied  { map } for   
pid=3157 comm="syzkaller455006" path="/root/syzkaller455006870" dev="sda1"  
ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023  
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
==================================================================
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 ffff8801c928fb70 by task syzkaller455006/3157

CPU: 0 PID: 3157 Comm: syzkaller455006 Not tainted 4.15.0-rc3+ #161
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:628 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:638
  ___sys_sendmsg+0x320/0x8b0 net/socket.c:2018
  __sys_sendmmsg+0x1ee/0x620 net/socket.c:2108
  SYSC_sendmmsg net/socket.c:2139 [inline]
  SyS_sendmmsg+0x35/0x60 net/socket.c:2134
  entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x43fe49
RSP: 002b:00007fffbe244ad8 EFLAGS: 00000217 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fe49
RDX: 0000000000000001 RSI: 000000002020c000 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000217 R12: 00000000004017b0
R13: 0000000000401840 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the page:
page:00000000b09dc24e 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:
  ffff8801c928fa00: 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f2
  ffff8801c928fa80: f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 00
> ffff8801c928fb00: 00 00 00 00 00 00 f2 f2 f2 f2 00 00 00 00 04 f2
                                                              ^
  ffff8801c928fb80: f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 00
  ffff8801c928fc00: 00 00 00 00 00 00 f3 f3 f3 f3 00 00 00 00 00 00
==================================================================