[syzbot] [mptcp?] KMSAN: uninit-value in mptcp_established_options

[syzbot <syzbot+ff020673c5e3d94d9478@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    08d0d3466664 Merge tag 'net-7.1-rc2' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15f6976c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1c3f61154f3bb7e5
dashboard link: https://syzkaller.appspot.com/bug?extid=ff020673c5e3d94d9478
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8688db3eb9ae/disk-08d0d346.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/72c570681077/vmlinux-08d0d346.xz
kernel image: https://storage.googleapis.com/syzbot-assets/21669c9bddcd/bzImage-08d0d346.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ff020673c5e3d94d9478@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in mptcp_write_data_fin net/mptcp/options.c:542 [inline]
BUG: KMSAN: uninit-value in mptcp_established_options_dss net/mptcp/options.c:590 [inline]
BUG: KMSAN: uninit-value in mptcp_established_options+0x112f/0x3530 net/mptcp/options.c:874
 mptcp_write_data_fin net/mptcp/options.c:542 [inline]
 mptcp_established_options_dss net/mptcp/options.c:590 [inline]
 mptcp_established_options+0x112f/0x3530 net/mptcp/options.c:874
 tcp_established_options+0x312/0xcc0 net/ipv4/tcp_output.c:1192
 __tcp_transmit_skb+0x5dc/0x5fe0 net/ipv4/tcp_output.c:1575
 __tcp_send_ack+0x967/0xad0 net/ipv4/tcp_output.c:4499
 tcp_send_ack+0x3d/0x60 net/ipv4/tcp_output.c:4505
 mptcp_subflow_shutdown+0x164/0x690 net/mptcp/protocol.c:3137
 mptcp_check_send_data_fin+0x31b/0x3d0 net/mptcp/protocol.c:3218
 __mptcp_wr_shutdown net/mptcp/protocol.c:3234 [inline]
 __mptcp_close+0x860/0x1360 net/mptcp/protocol.c:3313
 mptcp_close+0x42/0x260 net/mptcp/protocol.c:3367
 inet_release+0x1ee/0x2a0 net/ipv4/af_inet.c:442
 __sock_release net/socket.c:722 [inline]
 sock_close+0xd6/0x2f0 net/socket.c:1514
 __fput+0x60e/0x1010 fs/file_table.c:510
 ____fput+0x25/0x30 fs/file_table.c:538
 task_work_run+0x208/0x2b0 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
 exit_to_user_mode_loop+0x306/0x1b60 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 __do_fast_syscall_32+0x2c7/0x460 arch/x86/entry/syscall_32.c:310
 do_fast_syscall_32+0x37/0x80 arch/x86/entry/syscall_32.c:332
 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:370
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e

Local variable opts created at:
 __tcp_transmit_skb+0x4d/0x5fe0 net/ipv4/tcp_output.c:1536
 __tcp_send_ack+0x967/0xad0 net/ipv4/tcp_output.c:4499

CPU: 0 UID: 0 PID: 24584 Comm: syz.4.6812 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
=====================================================


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