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linux/net/mptcp
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Kuniyuki Iwashima 05f5e26d48 mptcp: Initialise rcv_mss before calling tcp_send_active_reset() in mptcp_do_fastclose(). 
commit f07f4ea53e upstream.

syzbot reported divide-by-zero in __tcp_select_window() by
MPTCP socket. [0]

We had a similar issue for the bare TCP and fixed in commit
499350a5a6 ("tcp: initialize rcv_mss to TCP_MIN_MSS instead
of 0").

Let's apply the same fix to mptcp_do_fastclose().

[0]:
Oops: divide error: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 6068 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:__tcp_select_window+0x824/0x1320 net/ipv4/tcp_output.c:3336
Code: ff ff ff 44 89 f1 d3 e0 89 c1 f7 d1 41 01 cc 41 21 c4 e9 a9 00 00 00 e8 ca 49 01 f8 e9 9c 00 00 00 e8 c0 49 01 f8 44 89 e0 99 <f7> 7c 24 1c 41 29 d4 48 bb 00 00 00 00 00 fc ff df e9 80 00 00 00
RSP: 0018:ffffc90003017640 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88807b469e40
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90003017730 R08: ffff888033268143 R09: 1ffff1100664d028
R10: dffffc0000000000 R11: ffffed100664d029 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  000055557faa0500(0000) GS:ffff888126135000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f64a1912ff8 CR3: 0000000072122000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 tcp_select_window net/ipv4/tcp_output.c:281 [inline]
 __tcp_transmit_skb+0xbc7/0x3aa0 net/ipv4/tcp_output.c:1568
 tcp_transmit_skb net/ipv4/tcp_output.c:1649 [inline]
 tcp_send_active_reset+0x2d1/0x5b0 net/ipv4/tcp_output.c:3836
 mptcp_do_fastclose+0x27e/0x380 net/mptcp/protocol.c:2793
 mptcp_disconnect+0x238/0x710 net/mptcp/protocol.c:3253
 mptcp_sendmsg_fastopen+0x2f8/0x580 net/mptcp/protocol.c:1776
 mptcp_sendmsg+0x1774/0x1980 net/mptcp/protocol.c:1855
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0xe5/0x270 net/socket.c:742
 __sys_sendto+0x3bd/0x520 net/socket.c:2244
 __do_sys_sendto net/socket.c:2251 [inline]
 __se_sys_sendto net/socket.c:2247 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2247
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f66e998f749
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffff9acedb8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007f66e9be5fa0 RCX: 00007f66e998f749
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007ffff9acee10 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f66e9be5fa0 R14: 00007f66e9be5fa0 R15: 0000000000000006
 </TASK>

Fixes: ae15506024 ("mptcp: fix duplicate reset on fastclose")
Reported-by: syzbot+3a92d359bc2ec6255a33@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/69260882.a70a0220.d98e3.00b4.GAE@google.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251125195331.309558-1-kuniyu@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-12-07 06:25:00 +09:00
..
bpf.c bpf: Add update_socket_protocol hook 2023-08-16 10:22:16 -07:00
crypto.c move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
crypto_test.c mptcp: fill in missing MODULE_DESCRIPTION() 2023-12-17 20:54:22 +00:00
ctrl.c mptcp: reset blackhole on success with non-loopback ifaces 2025-10-23 16:20:46 +02:00
diag.c mptcp: annotate data-races around subflow->fully_established 2024-12-14 20:03:52 +01:00
fastopen.c mptcp: pr_debug: add missing \n at the end 2024-08-27 14:45:16 -07:00
Kconfig kunit: mptcp: adhere to KUNIT formatting standard 2021-04-16 17:10:40 -07:00
Makefile net: mptcp: use policy generated by YAML spec 2023-10-24 13:00:32 -07:00
mib.c mptcp: prevent MPC handshake on port-based signal endpoints 2024-10-15 10:57:02 -07:00
mib.h mptcp: prevent MPC handshake on port-based signal endpoints 2024-10-15 10:57:02 -07:00
mptcp_diag.c mptcp: drop duplicate header inclusions 2024-03-06 20:24:10 -08:00
mptcp_pm_gen.c mptcp: no admin perm to list endpoints 2024-11-05 17:51:08 -08:00
mptcp_pm_gen.h mptcp: add token for get-addr in yaml 2024-03-04 13:07:45 +00:00
options.c mptcp: avoid unneeded subflow-level drops 2025-12-01 11:43:26 +01:00
pm.c mptcp: pm: in-kernel: usable client side with C-flag 2025-10-19 16:34:04 +02:00
pm_netlink.c mptcp: fix a race in mptcp_pm_del_add_timer() 2025-12-01 11:43:39 +01:00
pm_userspace.c mptcp: pm: userspace: flags: clearer msg if no remote addr 2025-05-29 11:02:56 +02:00
protocol.c mptcp: Initialise rcv_mss before calling tcp_send_active_reset() in mptcp_do_fastclose(). 2025-12-07 06:25:00 +09:00
protocol.h mptcp: decouple mptcp fastclose from tcp close 2025-12-01 11:43:27 +01:00
sched.c mptcp: pr_debug: add missing \n at the end 2024-08-27 14:45:16 -07:00
sockopt.c mptcp: sockopt: make sync_socket_options propagate SOCK_KEEPOPEN 2025-09-19 16:35:45 +02:00
subflow.c mptcp: Disallow MPTCP subflows from sockmap 2025-12-01 11:43:21 +01:00
syncookies.c mptcp: don't return sockets in foreign netns 2021-09-24 10:51:36 +01:00
token.c mptcp: add statistics for mptcp socket in use 2023-01-09 07:30:50 +00:00
token_test.c mptcp: token kunit: set protocol 2024-02-26 18:42:12 -08:00