syzbot


divide error in __tcp_select_window

Status: upstream: reported C repro on 2025/12/14 01:33
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+50aa7d3ef8f020d9a901@syzkaller.appspotmail.com
First crash: 19d, last: 12d
Bug presence (2)
Date Name Commit Repro Result
2025/12/14 linux-6.6.y (ToT) 5fa4793a2d2d C [report] divide error in __tcp_select_window
2025/12/14 upstream (ToT) 4a298a43f5e3 C Didn't crash
Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream divide error in __tcp_select_window (4) net 2 C done 14 36d 38d 28/29 upstream: reported C repro on 2025/11/25 19:50
upstream divide error in __tcp_select_window (2) net 2 C done 4 1728d 1730d 20/29 fixed on 2021/11/10 00:50
upstream divide error in __tcp_select_window (3) net 2 C 5 421d 426d 28/29 fixed on 2024/12/17 10:00
android-49 divide error in __tcp_select_window 2 2 3062d 3063d 0/3 closed as invalid on 2019/01/01 20:10
upstream divide error in __tcp_select_window net 2 C done 1119 1863d 1868d 19/29 fixed on 2021/03/10 01:48

Sample crash report:
divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 5919 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:__tcp_select_window+0x7a3/0x1270 net/ipv4/tcp_output.c:3114
Code: ff ff ff 44 89 e1 d3 e0 89 c1 f7 d1 41 01 ce 41 21 c6 e9 c5 00 00 00 e8 ab 9e 97 f8 e9 b8 00 00 00 e8 a1 9e 97 f8 44 89 f0 99 <f7> 7c 24 2c 41 29 d6 48 bb 00 00 00 00 00 fc ff df e9 9c 00 00 00
RSP: 0018:ffffc90003957b00 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff888026d75a00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90003957bf0 R08: ffff88801e780e93 R09: 1ffff11003cf01d2
R10: dffffc0000000000 R11: ffffed1003cf01d3 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffff888078a996e8
FS:  000055557ac56500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000180 CR3: 0000000073144000 CR4: 00000000003506e0
Call Trace:
 <TASK>
 tcp_select_window net/ipv4/tcp_output.c:276 [inline]
 __tcp_transmit_skb+0xb40/0x32a0 net/ipv4/tcp_output.c:1368
 tcp_transmit_skb net/ipv4/tcp_output.c:1440 [inline]
 tcp_send_active_reset+0x35e/0x6c0 net/ipv4/tcp_output.c:3593
 mptcp_do_fastclose+0x23a/0x310 net/mptcp/protocol.c:2820
 mptcp_disconnect+0x1fc/0x520 net/mptcp/protocol.c:3282
 inet_shutdown+0x1be/0x370 net/ipv4/af_inet.c:934
 __sys_shutdown_sock net/socket.c:2436 [inline]
 __sys_shutdown net/socket.c:2448 [inline]
 __do_sys_shutdown net/socket.c:2456 [inline]
 __se_sys_shutdown net/socket.c:2454 [inline]
 __x64_sys_shutdown+0x174/0x1d0 net/socket.c:2454
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f1872f8f749
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:00007ffc6d7f6508 EFLAGS: 00000246 ORIG_RAX: 0000000000000030
RAX: ffffffffffffffda RBX: 00007f18731e5fa0 RCX: 00007f1872f8f749
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f1873013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f18731e5fa0 R14: 00007f18731e5fa0 R15: 0000000000000002
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__tcp_select_window+0x7a3/0x1270 net/ipv4/tcp_output.c:3114
Code: ff ff ff 44 89 e1 d3 e0 89 c1 f7 d1 41 01 ce 41 21 c6 e9 c5 00 00 00 e8 ab 9e 97 f8 e9 b8 00 00 00 e8 a1 9e 97 f8 44 89 f0 99 <f7> 7c 24 2c 41 29 d6 48 bb 00 00 00 00 00 fc ff df e9 9c 00 00 00
RSP: 0018:ffffc90003957b00 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff888026d75a00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90003957bf0 R08: ffff88801e780e93 R09: 1ffff11003cf01d2
R10: dffffc0000000000 R11: ffffed1003cf01d3 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ffff888078a996e8
FS:  000055557ac56500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000180 CR3: 0000000073144000 CR4: 00000000003506e0
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	ff 44 89 e1          	incl   -0x1f(%rcx,%rcx,4)
   4:	d3 e0                	shl    %cl,%eax
   6:	89 c1                	mov    %eax,%ecx
   8:	f7 d1                	not    %ecx
   a:	41 01 ce             	add    %ecx,%r14d
   d:	41 21 c6             	and    %eax,%r14d
  10:	e9 c5 00 00 00       	jmp    0xda
  15:	e8 ab 9e 97 f8       	call   0xf8979ec5
  1a:	e9 b8 00 00 00       	jmp    0xd7
  1f:	e8 a1 9e 97 f8       	call   0xf8979ec5
  24:	44 89 f0             	mov    %r14d,%eax
  27:	99                   	cltd
* 28:	f7 7c 24 2c          	idivl  0x2c(%rsp) <-- trapping instruction
  2c:	41 29 d6             	sub    %edx,%r14d
  2f:	48 bb 00 00 00 00 00 	movabs $0xdffffc0000000000,%rbx
  36:	fc ff df
  39:	e9 9c 00 00 00       	jmp    0xda

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/14 03:03 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan divide error in __tcp_select_window
2025/12/14 02:31 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan divide error in __tcp_select_window
2025/12/14 02:02 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan divide error in __tcp_select_window
2025/12/21 13:27 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan divide error in __tcp_select_window
2025/12/21 13:27 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan divide error in __tcp_select_window
2025/12/14 01:32 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan divide error in __tcp_select_window
* Struck through repros no longer work on HEAD.