==================================================================
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 ffff8801c89efb70 by task syzkaller036649/3149

CPU: 0 PID: 3149 Comm: syzkaller036649 Not tainted 4.15.0-rc4-mm1+ #48
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:256
 kasan_report_error mm/kasan/report.c:355 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:413
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:434
 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:00007ffefa4b0438 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:ffffea0007227bc0 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: 0000000000000000 ffffea0007220101 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801c89efa00: 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f2
 ffff8801c89efa80: f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 00
>ffff8801c89efb00: 00 00 00 00 00 00 f2 f2 f2 f2 00 00 00 00 04 f2
                                                             ^
 ffff8801c89efb80: f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 00 00
 ffff8801c89efc00: 00 00 00 00 00 00 f3 f3 f3 f3 00 00 00 00 00 00
==================================================================