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

[syzbot]

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: syzbot+d101e1...@syzkaller.appspotmail.com

=====================================================
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.
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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

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

net/sctp/inqueue.c:123:34: error: use of undeclared identifier 'gfp'


Tested on:

commit: 552c5071 Merge tag 'vfio-v6.18-rc3' of https://github...
git tree: upstream

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

patch: https://syzkaller.appspot.com/x/patch.diff?x=1044ce7c580000

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KMSAN: uninit-value in sctp_inq_pop

=====================================================
BUG: KMSAN: uninit-value in sctp_inq_pop+0x159c/0x1aa0 net/sctp/inqueue.c:213
sctp_inq_pop+0x159c/0x1aa0 net/sctp/inqueue.c:213

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+0x150b/0x1aa0 net/sctp/inqueue.c:209

CPU: 1 UID: 0 PID: 6609 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(none)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
=====================================================

Tested on:

commit: 552c5071 Merge tag 'vfio-v6.18-rc3' of https://github...
git tree: upstream

console output: https://syzkaller.appspot.com/x/log.txt?x=145e2d42580000

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

patch: https://syzkaller.appspot.com/x/patch.diff?x=165fd734580000

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: Re: [syzbot] [sctp?] KMSAN: uninit-value in sctp_inq_pop (3)
Author: vnranga...@gmail.com

#syz test

On Wed, Oct 22, 2025 at 5:23 PM syzbot <
syzbot+d101e1...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still
> triggering an issue:
> KMSAN: uninit-value in sctp_inq_pop
>

> =====================================================

> BUG: KMSAN: uninit-value in sctp_inq_pop+0x159c/0x1aa0
> net/sctp/inqueue.c:213
> sctp_inq_pop+0x159c/0x1aa0 net/sctp/inqueue.c:213

> 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+0x150b/0x1aa0 net/sctp/inqueue.c:209

> CPU: 1 UID: 0 PID: 6609 Comm: syz.0.18 Not tainted syzkaller #0

> PREEMPT(none)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 10/02/2025
> =====================================================
>
>

> Tested on:
>
> commit: 552c5071 Merge tag 'vfio-v6.18-rc3' of https://github...

> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=145e2d42580000

> 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

> patch:
> https://syzkaller.appspot.com/x/patch.diff?x=165fd734580000
>
>

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+d101e1...@syzkaller.appspotmail.com
Tested-by: syzbot+d101e1...@syzkaller.appspotmail.com

Tested on:

commit: dd72c8fc Merge tag 'platform-drivers-x86-v6.18-2' of g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10aed3e2580000

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

patch: https://syzkaller.appspot.com/x/patch.diff?x=10bee3e2580000

Note: testing is done by a robot and is best-effort only.

[Ranganath V N]

#syz test

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
checking file net/sctp/input.c
patch: **** unexpected end of file in patch



Tested on:

commit: ab431bc3 Merge tag 'net-6.18-rc3' of git://git.kernel...

git tree: upstream
kernel config: https://syzkaller.appspot.com/x/.config?x=bbd3e7f3c2e28265
dashboard link: https://syzkaller.appspot.com/bug?extid=d101e12bccd4095460e7
compiler:

patch: https://syzkaller.appspot.com/x/patch.diff?x=12cec3e2580000

[Ranganath V N]

#syz test

diff --git a/net/sctp/input.c b/net/sctp/input.c
index 7e99894778d4..e119e460ccde 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -190,7 +190,7 @@ int sctp_rcv(struct sk_buff *skb)
                goto discard_release;
        nf_reset_ct(skb);
 
-       if (sk_filter(sk, skb))
+       if (sk_filter(sk, skb) || skb->len < sizeof(struct sctp_chunkhdr))
                goto discard_release;
 
        /* Create an SCTP packet structure. */