syzbot


divide error in __tcp_select_window (4)

Status: upstream: reported C repro on 2025/11/25 19:50
Subsystems: net
[Documentation on labels]
Reported-by: syzbot+3a92d359bc2ec6255a33@syzkaller.appspotmail.com
First crash: 4d10h, last: 18m
Cause bisection: introduced by (bisect log) :
commit ae155060247be8dcae3802a95bd1bdf93ab3215d
Author: Paolo Abeni <pabeni@redhat.com>
Date: Tue Nov 18 07:20:24 2025 +0000

  mptcp: fix duplicate reset on fastclose

Crash: divide error in __tcp_select_window (log)
Repro: C syz .config
  
Discussions (2)
Title Replies (including bot) Last reply
[PATCH v1 net-next] mptcp: Initialise rcv_mss before calling tcp_send_active_reset() in mptcp_do_fastclose(). 1 (1) 2025/11/25 19:53
[syzbot] [net?] divide error in __tcp_select_window (4) 0 (1) 2025/11/25 19:50
Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream divide error in __tcp_select_window (2) net 2 C done 4 1691d 1692d 20/29 fixed on 2021/11/10 00:50
upstream divide error in __tcp_select_window (3) net 2 C 5 383d 388d 28/29 fixed on 2024/12/17 10:00
android-49 divide error in __tcp_select_window 2 2 3024d 3025d 0/3 closed as invalid on 2019/01/01 20:10
upstream divide error in __tcp_select_window net 2 C done 1119 1825d 1830d 19/29 fixed on 2021/03/10 01:48

Sample crash report:
RBP: 00007ffff9acee10 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f66e9be5fa0 R14: 00007f66e9be5fa0 R15: 0000000000000006
 </TASK>
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>
Modules linked in:
---[ end trace 0000000000000000 ]---
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
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	ff 44 89 f1          	incl   -0xf(%rcx,%rcx,4)
   4:	d3 e0                	shl    %cl,%eax
   6:	89 c1                	mov    %eax,%ecx
   8:	f7 d1                	not    %ecx
   a:	41 01 cc             	add    %ecx,%r12d
   d:	41 21 c4             	and    %eax,%r12d
  10:	e9 a9 00 00 00       	jmp    0xbe
  15:	e8 ca 49 01 f8       	call   0xf80149e4
  1a:	e9 9c 00 00 00       	jmp    0xbb
  1f:	e8 c0 49 01 f8       	call   0xf80149e4
  24:	44 89 e0             	mov    %r12d,%eax
  27:	99                   	cltd
* 28:	f7 7c 24 1c          	idivl  0x1c(%rsp) <-- trapping instruction
  2c:	41 29 d4             	sub    %edx,%r12d
  2f:	48 bb 00 00 00 00 00 	movabs $0xdffffc0000000000,%rbx
  36:	fc ff df
  39:	e9 80 00 00 00       	jmp    0xbe

Crashes (9):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/21 18:56 net-next e2c20036a887 c31c1b0b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce divide error in __tcp_select_window
2025/11/21 18:19 net-next e2c20036a887 c31c1b0b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce divide error in __tcp_select_window
2025/11/21 16:42 net-next e2c20036a887 c31c1b0b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce divide error in __tcp_select_window
2025/11/25 13:54 upstream ac3fd01e4c1e 64219f15 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root divide error in __tcp_select_window
2025/11/23 17:49 upstream d13f3ac64efb 4fb8ef37 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root divide error in __tcp_select_window
2025/11/22 07:50 upstream 2eba5e05d9bc c31c1b0b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root divide error in __tcp_select_window
2025/11/26 02:04 upstream 8a2bcda5e139 64219f15 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 divide error in __tcp_select_window
2025/11/26 00:18 upstream 8a2bcda5e139 64219f15 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 divide error in __tcp_select_window
2025/11/21 15:44 net-next e2c20036a887 c31c1b0b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-kasan-gce divide error in __tcp_select_window
* Struck through repros no longer work on HEAD.