netdev - [syzbot] [net?] KMSAN: uninit-value in lec_atm

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Message-ID: <69298e9d.a70a0220.d98e3.013a.GAE@google.com>
Date: Fri, 28 Nov 2025 03:59:25 -0800
From: syzbot <syzbot+5dd615f890ddada54057@...kaller.appspotmail.com>
To: davem@...emloft.net, edumazet@...gle.com, horms@...nel.org, 
	kuba@...nel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [net?] KMSAN: uninit-value in lec_atm_send

Hello,

syzbot found the following issue on:

HEAD commit:    ac3fd01e4c1e Linux 6.18-rc7
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=139a1612580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=61a9bf3cc5d17a01
dashboard link: https://syzkaller.appspot.com/bug?extid=5dd615f890ddada54057
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=10f4b8b4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=129d0e58580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/227434a45737/disk-ac3fd01e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d8117003dbb5/vmlinux-ac3fd01e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a13125fb7a7d/bzImage-ac3fd01e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5dd615f890ddada54057@...kaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in lec_arp_update net/atm/lec.c:1845 [inline]
BUG: KMSAN: uninit-value in lec_atm_send+0x2b02/0x55b0 net/atm/lec.c:385
 lec_arp_update net/atm/lec.c:1845 [inline]
 lec_atm_send+0x2b02/0x55b0 net/atm/lec.c:385
 vcc_sendmsg+0x1052/0x1190 net/atm/common.c:650
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x333/0x3d0 net/socket.c:742
 ____sys_sendmsg+0x7e0/0xd80 net/socket.c:2630
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2684
 __sys_sendmsg net/socket.c:2716 [inline]
 __do_sys_sendmsg net/socket.c:2721 [inline]
 __se_sys_sendmsg net/socket.c:2719 [inline]
 __x64_sys_sendmsg+0x211/0x3e0 net/socket.c:2719
 x64_sys_call+0x1dfd/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:47
 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:4985 [inline]
 slab_alloc_node mm/slub.c:5288 [inline]
 kmem_cache_alloc_node_noprof+0x989/0x16b0 mm/slub.c:5340
 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]
 vcc_sendmsg+0x602/0x1190 net/atm/common.c:628
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg+0x333/0x3d0 net/socket.c:742
 ____sys_sendmsg+0x7e0/0xd80 net/socket.c:2630
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2684
 __sys_sendmsg net/socket.c:2716 [inline]
 __do_sys_sendmsg net/socket.c:2721 [inline]
 __se_sys_sendmsg net/socket.c:2719 [inline]
 __x64_sys_sendmsg+0x211/0x3e0 net/socket.c:2719
 x64_sys_call+0x1dfd/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:47
 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: 6068 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(none) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
=====================================================


---
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 syzkaller@...glegroups.com.

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:
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(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