Re: general protection fault in rds_recv_rcvbuf_delta

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    cd984a5be215 Merge tag 'xtensa-20190201' of git://github.c..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1725e4ff400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2e0064f906afee10
dashboard link: https://syzkaller.appspot.com/bug?extid=4b4f8163c2e246df3c4c
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11631328c00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1172c7ef400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4b4f8163c2e246df3c4c@xxxxxxxxxxxxxxxxxxxxxxxxx

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 8054 Comm: syz-executor390 Not tainted 5.0.0-rc4+ #56
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:rds_recv_rcvbuf_delta.part.0+0x14a/0x3f0 net/rds/recv.c:103
Code: c1 ea 03 80 3c 02 00 0f 85 6e 02 00 00 4c 8b a3 c0 04 00 00 48 b8 00  
00 00 00 00 fc ff df 49 8d 7c 24 2c 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48  
89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 00
RSP: 0018:ffff88808fd9f670 EFLAGS: 00010007
RAX: dffffc0000000000 RBX: ffff8880a96a97c0 RCX: ffffffff8681f5bd
RDX: 0000000000000005 RSI: ffffffff8681f5cb RDI: 000000000000002c
RBP: ffff88808fd9f6a8 R08: ffff888086a1a000 R09: ffffed1011fb3ec4
R10: ffffed1011fb3ec3 R11: 0000000000000003 R12: 0000000000000000
R13: ffff8880a96a9ce4 R14: 000000000002e400 R15: ffff88809aeecc00
FS:  00000000026d4940(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000424ec0 CR3: 000000008e163000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 rds_recv_rcvbuf_delta net/rds/recv.c:379 [inline]
 rds_recv_incoming+0x789/0x11f0 net/rds/recv.c:379
 rds_loop_xmit+0xf3/0x2a0 net/rds/loop.c:96
 rds_send_xmit+0x1113/0x2560 net/rds/send.c:355
 rds_sendmsg+0x280a/0x3450 net/rds/send.c:1368
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xdd/0x130 net/socket.c:631
 ___sys_sendmsg+0x806/0x930 net/socket.c:2116
 __sys_sendmsg+0x105/0x1d0 net/socket.c:2154
 __do_sys_sendmsg net/socket.c:2163 [inline]
 __se_sys_sendmsg net/socket.c:2161 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4487e9
Code: e8 4c e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 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 ab c5 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffa307f188 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004487e9
RDX: 0000000000000000 RSI: 0000000020000340 RDI: 0000000000000004
RBP: 000000000000c806 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004ab4b0
R13: 00000000004052b0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace e9dbe4e38be82e2e ]---
RIP: 0010:rds_recv_rcvbuf_delta.part.0+0x14a/0x3f0 net/rds/recv.c:103
Code: c1 ea 03 80 3c 02 00 0f 85 6e 02 00 00 4c 8b a3 c0 04 00 00 48 b8 00  
00 00 00 00 fc ff df 49 8d 7c 24 2c 48 89 fa 48 c1 ea 03 <0f> b6 14 02 48  
89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 00
RSP: 0018:ffff88808fd9f670 EFLAGS: 00010007
RAX: dffffc0000000000 RBX: ffff8880a96a97c0 RCX: ffffffff8681f5bd
RDX: 0000000000000005 RSI: ffffffff8681f5cb RDI: 000000000000002c
RBP: ffff88808fd9f6a8 R08: ffff888086a1a000 R09: ffffed1011fb3ec4
R10: ffffed1011fb3ec3 R11: 0000000000000003 R12: 0000000000000000
R13: ffff8880a96a9ce4 R14: 000000000002e400 R15: ffff88809aeecc00
FS:  00000000026d4940(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000424ec0 CR3: 000000008e163000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400