WARNING in warn_bad_map

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11124521100000
kernel config: https://syzkaller.appspot.com/x/.config?x=d195fe572fb15312
dashboard link: https://syzkaller.appspot.com/bug?extid=42a07faa5923cfaeb9c9
compiler: gcc (GCC) 9.0.0 20181231 (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:
Reported-by: syzbot+42a07f...@syzkaller.appspotmail.com

------------[ cut here ]------------
Bad mapping: ssn=2478501 map_seq=0 map_data_len=32748
WARNING: CPU: 0 PID: 20706 at net/mptcp/subflow.c:581 warn_bad_map.isra.0.part.0+0x7d/0xb0 net/mptcp/subflow.c:581
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 20706 Comm: syz-executor.2 Not tainted 5.7.0-syzkaller #0
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+0x188/0x20d lib/dump_stack.c:118
panic+0x2e3/0x75c kernel/panic.c:221
__warn.cold+0x2f/0x35 kernel/panic.c:582
report_bug+0x27b/0x2f0 lib/bug.c:195
fixup_bug arch/x86/kernel/traps.c:105 [inline]
fixup_bug arch/x86/kernel/traps.c:100 [inline]
do_error_trap+0x12b/0x220 arch/x86/kernel/traps.c:197
do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:216
invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:warn_bad_map.isra.0.part.0+0x7d/0xb0 net/mptcp/subflow.c:581
Code: 48 c1 ea 03 0f b6 14 02 48 89 d8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 1c 8b 13 44 89 e6 48 c7 c7 20 5c fe 88 e8 4b 2e 6b f9 <0f> 0b 48 83 c4 08 5b 5d 41 5c c3 48 89 df 89 4c 24 04 e8 7c 3f d9
RSP: 0018:ffffc90006f2f420 EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffff88809e4fe43c RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff815d5ba7 RDI: fffff52000de5e76
RBP: ffff88809e4fe444 R08: ffff8880850aa580 R09: 0000000000000001
R10: ffffffff8c347a27 R11: fffffbfff1868f44 R12: 000000000025d1a5
R13: ffff88809e4fe400 R14: ffff88809e4fe444 R15: ffff88809e4fe43c
warn_bad_map net/mptcp/subflow.c:613 [inline]
validate_mapping net/mptcp/subflow.c:613 [inline]
get_mapping_status net/mptcp/subflow.c:728 [inline]
subflow_check_data_avail net/mptcp/subflow.c:766 [inline]
mptcp_subflow_data_available+0x145b/0x1aa0 net/mptcp/subflow.c:862
subflow_data_ready+0x10b/0x170 net/mptcp/subflow.c:903
tcp_data_ready+0xe8/0x230 net/ipv4/tcp_input.c:4776
tcp_data_queue+0x1161/0x4760 net/ipv4/tcp_input.c:4842
tcp_rcv_established+0x905/0x1d90 net/ipv4/tcp_input.c:5735
tcp_v4_do_rcv+0x605/0x8b0 net/ipv4/tcp_ipv4.c:1629
sk_backlog_rcv include/net/sock.h:996 [inline]
__release_sock+0x134/0x3a0 net/core/sock.c:2548
release_sock+0x54/0x1b0 net/core/sock.c:3064
mptcp_sendmsg+0x11f9/0x17f0 net/mptcp/protocol.c:872
inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:814
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:672
sock_write_iter+0x288/0x3c0 net/socket.c:999
call_write_iter include/linux/fs.h:1917 [inline]
do_iter_readv_writev+0x51e/0x790 fs/read_write.c:694
do_iter_write fs/read_write.c:999 [inline]
do_iter_write+0x18b/0x600 fs/read_write.c:980
vfs_writev+0x1b3/0x2f0 fs/read_write.c:1072
do_writev+0x27f/0x300 fs/read_write.c:1115
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45ca59
Code: 0d b7 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 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f5887229c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 000000000050e320 RCX: 000000000045ca59
RDX: 0000000000000001 RSI: 0000000020000200 RDI: 0000000000000004
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000d43 R14: 00000000004cb67f R15: 00007f588722a6d4
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[Paolo Abeni]

[stripping some recipients, since the following should be syzbot-
specific]

On Mon, 2020-06-22 at 02:30 -0700, syzbot wrote:
> syzbot found the following crash on:
>
> HEAD commit: 7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11124521100000
> kernel config: https://syzkaller.appspot.com/x/.config?x=d195fe572fb15312
> dashboard link: https://syzkaller.appspot.com/bug?extid=42a07faa5923cfaeb9c9
> compiler: gcc (GCC) 9.0.0 20181231 (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:
> Reported-by: syzbot+42a07f...@syzkaller.appspotmail.com

This should be fixed by the combination of commit 0e7bc442b405 ("mptcp:
fix DSS map generation on fin retransmission") (currently on -net) and
commit 13f1555c1b4c49b8ab9dd80b7353deec0526ccac (currently only on net-
next).

In not clear to me how to communicate the above to syzbot. Any
suggestion more than welcome!

Thanks,

Paolo

[Dmitry Vyukov]

Hi Paolo,

Yes, there is no way to attach to fixing commits via email interface.
But if both are required to stop this WARNING from happening, we can
mark it as fixed by the one that is supposed to propagate to all trees
later. I guess it's the one in net-next?

[Paolo Abeni]

Thank you for the prompt reply!

Yes, the net-next commit will land into vanilla later - in some weeks
from now.

Should I wait for that event to send a '#syz fix: ' reply? I fear
otherwise syzbot may test a [net-next] tree without the first mentioned
commit and still hit the issue.

Cheers,

Paolo

[Dmitry Vyukov]

https://goo.gl/tpsmEJ#bug-status-tracking should answer your question
(or we need to improve the docs).

I see the commit you mentioned
13f1555c1b4c49b8ab9dd80b7353deec0526ccac is actually a merge:
Merge branch 'MPTCP-improve-fallback-to-TCP'
I guess what fixes it is a particular non-merge commit, right? What is
it? The syzbot referenced commits are considered for stable trees, and
a merge is not very useful for backporting.

[Paolo Abeni]

[sorry for lagging behind]

On Wed, 2020-07-08 at 10:42 +0200, Dmitry Vyukov wrote:
> On Tue, Jul 7, 2020 at 6:39 PM Paolo Abeni <pab...@redhat.com> wrote:
> > Should I wait for that event to send a '#syz fix: ' reply? I fear
> > otherwise syzbot may test a [net-next] tree without the first mentioned
> > commit and still hit the issue.
>
> https://goo.gl/tpsmEJ#bug-status-tracking should answer your question
> (or we need to improve the docs).

Indeed it answer in a clear way, thanks for the pointer

> I see the commit you mentioned
> 13f1555c1b4c49b8ab9dd80b7353deec0526ccac is actually a merge:
> Merge branch 'MPTCP-improve-fallback-to-TCP'
> I guess what fixes it is a particular non-merge commit, right? What is
> it? The syzbot referenced commits are considered for stable trees, and
> a merge is not very useful for backporting.

The relevant non-merge commit should be:

commit e1ff9e82e2ea53d01540692a85c16a77e1089537
Author: Davide Caratti <dcar...@redhat.com>
Date: Mon Jun 29 22:26:20 2020 +0200

net: mptcp: improve fallback to TCP

but that is part of a code re-factor, really not suitable for stable
branch IMHO.

Thanks,

Paolo