git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From f07f4ea53e22429c84b20832fa098b5ecc0d4e35 Mon Sep 17 00:00:00 2001
   2 From: Kuniyuki Iwashima <kuniyu@google.com>
   3 Date: Tue, 25 Nov 2025 19:53:29 +0000
   4 Subject: mptcp: Initialise rcv_mss before calling tcp_send_active_reset() in mptcp_do_fastclose().
   5
   6 From: Kuniyuki Iwashima <kuniyu@google.com>
   7
   8 commit f07f4ea53e22429c84b20832fa098b5ecc0d4e35 upstream.
   9
  10 syzbot reported divide-by-zero in __tcp_select_window() by
  11 MPTCP socket. [0]
  12
  13 We had a similar issue for the bare TCP and fixed in commit
  14 499350a5a6e7 ("tcp: initialize rcv_mss to TCP_MIN_MSS instead
  15 of 0").
  16
  17 Let's apply the same fix to mptcp_do_fastclose().
  18
  19 [0]:
  20 Oops: divide error: 0000 [#1] SMP KASAN PTI
  21 CPU: 0 UID: 0 PID: 6068 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
  22 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
  23 RIP: 0010:__tcp_select_window+0x824/0x1320 net/ipv4/tcp_output.c:3336
  24 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
  25 RSP: 0018:ffffc90003017640 EFLAGS: 00010293
  26 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88807b469e40
  27 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
  28 RBP: ffffc90003017730 R08: ffff888033268143 R09: 1ffff1100664d028
  29 R10: dffffc0000000000 R11: ffffed100664d029 R12: 0000000000000000
  30 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
  31 FS:  000055557faa0500(0000) GS:ffff888126135000(0000) knlGS:0000000000000000
  32 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  33 CR2: 00007f64a1912ff8 CR3: 0000000072122000 CR4: 00000000003526f0
  34 Call Trace:
  35  <TASK>
  36  tcp_select_window net/ipv4/tcp_output.c:281 [inline]
  37  __tcp_transmit_skb+0xbc7/0x3aa0 net/ipv4/tcp_output.c:1568
  38  tcp_transmit_skb net/ipv4/tcp_output.c:1649 [inline]
  39  tcp_send_active_reset+0x2d1/0x5b0 net/ipv4/tcp_output.c:3836
  40  mptcp_do_fastclose+0x27e/0x380 net/mptcp/protocol.c:2793
  41  mptcp_disconnect+0x238/0x710 net/mptcp/protocol.c:3253
  42  mptcp_sendmsg_fastopen+0x2f8/0x580 net/mptcp/protocol.c:1776
  43  mptcp_sendmsg+0x1774/0x1980 net/mptcp/protocol.c:1855
  44  sock_sendmsg_nosec net/socket.c:727 [inline]
  45  __sock_sendmsg+0xe5/0x270 net/socket.c:742
  46  __sys_sendto+0x3bd/0x520 net/socket.c:2244
  47  __do_sys_sendto net/socket.c:2251 [inline]
  48  __se_sys_sendto net/socket.c:2247 [inline]
  49  __x64_sys_sendto+0xde/0x100 net/socket.c:2247
  50  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
  51  do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
  52  entry_SYSCALL_64_after_hwframe+0x77/0x7f
  53 RIP: 0033:0x7f66e998f749
  54 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
  55 RSP: 002b:00007ffff9acedb8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
  56 RAX: ffffffffffffffda RBX: 00007f66e9be5fa0 RCX: 00007f66e998f749
  57 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
  58 RBP: 00007ffff9acee10 R08: 0000000000000000 R09: 0000000000000000
  59 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
  60 R13: 00007f66e9be5fa0 R14: 00007f66e9be5fa0 R15: 0000000000000006
  61  </TASK>
  62
  63 Fixes: ae155060247b ("mptcp: fix duplicate reset on fastclose")
  64 Reported-by: syzbot+3a92d359bc2ec6255a33@syzkaller.appspotmail.com
  65 Closes: https://lore.kernel.org/netdev/69260882.a70a0220.d98e3.00b4.GAE@google.com/
  66 Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
  67 Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
  68 Cc: stable@vger.kernel.org
  69 Link: https://patch.msgid.link/20251125195331.309558-1-kuniyu@google.com
  70 Signed-off-by: Paolo Abeni <pabeni@redhat.com>
  71 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  72 ---
  73  net/mptcp/protocol.c |    6 ++++++
  74  1 file changed, 6 insertions(+)
  75
  76 --- a/net/mptcp/protocol.c
  77 +++ b/net/mptcp/protocol.c
  78 @@ -2854,6 +2854,12 @@ static void mptcp_do_fastclose(struct so
  79                         goto unlock;
  80
  81                 subflow->send_fastclose = 1;
  82 +
  83 +               /* Initialize rcv_mss to TCP_MIN_MSS to avoid division by 0
  84 +                * issue in __tcp_select_window(), see tcp_disconnect().
  85 +                */
  86 +               inet_csk(ssk)->icsk_ack.rcv_mss = TCP_MIN_MSS;
  87 +
  88                 tcp_send_active_reset(ssk, ssk->sk_allocation,
  89                                       SK_RST_REASON_TCP_ABORT_ON_CLOSE);
  90  unlock: