Subject: [syzbot] [sctp?] KMSAN: uninit-value in sctp_inq_pop (3)

From: syzbot <[email-masked]>
Date: Mon, 20 Oct 2025 08:48:29 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    d9043c79ba68 Merge tag 'sched_urgent_for_v6.18_rc2' of git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11168de2580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bbd3e7f3c2e28265
dashboard link: https://syzkaller.appspot.com/bug?extid=d101e12bccd4095460e7
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14098d42580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=118a9734580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/57a87b0986c0/disk-d9043c79.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/019c87e1df0a/vmlinux-d9043c79.xz
kernel image: https://storage.googleapis.com/syzbot-assets/54f8a8b0734b/bzImage-d9043c79.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

=====================================================
BUG: KMSAN: uninit-value in sctp_inq_pop+0x14dc/0x19e0 net/sctp/inqueue.c:211
 sctp_inq_pop+0x14dc/0x19e0 net/sctp/inqueue.c:211
 sctp_assoc_bh_rcv+0x1a0/0xbc0 net/sctp/associola.c:980
 sctp_inq_push+0x2a6/0x350 net/sctp/inqueue.c:88
 sctp_backlog_rcv+0x3c7/0xda0 net/sctp/input.c:331
 sk_backlog_rcv+0x142/0x420 include/net/sock.h:1158
 __release_sock+0x1ef/0x380 net/core/sock.c:3180
 release_sock+0x6b/0x270 net/core/sock.c:3735
 sctp_sendmsg+0x3a2b/0x49f0 net/sctp/socket.c:2036
 inet_sendmsg+0x26c/0x2a0 net/ipv4/af_inet.c:853
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x278/0x3d0 net/socket.c:742
 sock_sendmsg+0x170/0x280 net/socket.c:765
 splice_to_socket+0x10e6/0x1a60 fs/splice.c:886
 do_splice_from fs/splice.c:938 [inline]
 do_splice+0x1fd2/0x30d0 fs/splice.c:1351
 __do_splice fs/splice.c:1433 [inline]
 __do_sys_splice fs/splice.c:1636 [inline]
 __se_sys_splice+0x549/0x8c0 fs/splice.c:1618
 __x64_sys_splice+0x114/0x1a0 fs/splice.c:1618
 x64_sys_call+0x3140/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:276
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
 sctp_inq_pop+0x144a/0x19e0 net/sctp/inqueue.c:207
 sctp_assoc_bh_rcv+0x1a0/0xbc0 net/sctp/associola.c:980
 sctp_inq_push+0x2a6/0x350 net/sctp/inqueue.c:88
 sctp_backlog_rcv+0x3c7/0xda0 net/sctp/input.c:331
 sk_backlog_rcv+0x142/0x420 include/net/sock.h:1158
 __release_sock+0x1ef/0x380 net/core/sock.c:3180
 release_sock+0x6b/0x270 net/core/sock.c:3735
 sctp_sendmsg+0x3a2b/0x49f0 net/sctp/socket.c:2036
 inet_sendmsg+0x26c/0x2a0 net/ipv4/af_inet.c:853
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x278/0x3d0 net/socket.c:742
 sock_sendmsg+0x170/0x280 net/socket.c:765
 splice_to_socket+0x10e6/0x1a60 fs/splice.c:886
 do_splice_from fs/splice.c:938 [inline]
 do_splice+0x1fd2/0x30d0 fs/splice.c:1351
 __do_splice fs/splice.c:1433 [inline]
 __do_sys_splice fs/splice.c:1636 [inline]
 __se_sys_splice+0x549/0x8c0 fs/splice.c:1618
 __x64_sys_splice+0x114/0x1a0 fs/splice.c:1618
 x64_sys_call+0x3140/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:276
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:
 slab_post_alloc_hook mm/slub.c:4969 [inline]
 slab_alloc_node mm/slub.c:5272 [inline]
 kmem_cache_alloc_node_noprof+0x989/0x16b0 mm/slub.c:5324
 kmalloc_reserve+0x13c/0x4b0 net/core/skbuff.c:579
 __alloc_skb+0x347/0x7d0 net/core/skbuff.c:670
 alloc_skb include/linux/skbuff.h:1383 [inline]
 sctp_packet_transmit+0x44b/0x46d0 net/sctp/output.c:598
 sctp_outq_flush_transports net/sctp/outqueue.c:1173 [inline]
 sctp_outq_flush+0x1c7d/0x67c0 net/sctp/outqueue.c:1221
 sctp_outq_uncork+0x9e/0xc0 net/sctp/outqueue.c:764
 sctp_cmd_interpreter net/sctp/sm_sideeffect.c:-1 [inline]
 sctp_side_effects net/sctp/sm_sideeffect.c:1204 [inline]
 sctp_do_sm+0x8c8e/0x9720 net/sctp/sm_sideeffect.c:1175
 sctp_primitive_SEND+0xd7/0x110 net/sctp/primitive.c:163
 sctp_sendmsg_to_asoc+0x1db8/0x2250 net/sctp/socket.c:1873
 sctp_sendmsg+0x3910/0x49f0 net/sctp/socket.c:2031
 inet_sendmsg+0x26c/0x2a0 net/ipv4/af_inet.c:853
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x278/0x3d0 net/socket.c:742
 sock_sendmsg+0x170/0x280 net/socket.c:765
 splice_to_socket+0x10e6/0x1a60 fs/splice.c:886
 do_splice_from fs/splice.c:938 [inline]
 do_splice+0x1fd2/0x30d0 fs/splice.c:1351
 __do_splice fs/splice.c:1433 [inline]
 __do_sys_splice fs/splice.c:1636 [inline]
 __se_sys_splice+0x549/0x8c0 fs/splice.c:1618
 __x64_sys_splice+0x114/0x1a0 fs/splice.c:1618
 x64_sys_call+0x3140/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:276
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 0 UID: 0 PID: 6071 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(none) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
=====================================================

---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at [email-masked].

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup