[syzbot] [wireless?] KMSAN: uninit-value in cfg80211_classify8021d

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 98ac9cc4b445 Merge tag 'f2fs-fix-6.18-rc2' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16be6734580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bbd3e7f3c2e28265
dashboard link: https://syzkaller.appspot.com/bug?extid=878ddc3962f792e9af59
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=111e7dcd980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1223a492580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f8ad8459a8da/disk-98ac9cc4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/28720fa307c1/vmlinux-98ac9cc4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e4f310acec99/bzImage-98ac9cc4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+878ddc...@syzkaller.appspotmail.com

mac80211_hwsim hwsim5 wlan1: entered allmulticast mode
=====================================================
BUG: KMSAN: uninit-value in cfg80211_classify8021d+0x99d/0x12b0 net/wireless/util.c:1027
cfg80211_classify8021d+0x99d/0x12b0 net/wireless/util.c:1027
ieee80211_select_queue+0x37a/0x9e0 net/mac80211/wme.c:180
__ieee80211_subif_start_xmit+0x60f/0x1d90 net/mac80211/tx.c:4304
ieee80211_subif_start_xmit+0xa8/0x6d0 net/mac80211/tx.c:4538
__netdev_start_xmit include/linux/netdevice.h:5248 [inline]
netdev_start_xmit include/linux/netdevice.h:5257 [inline]
xmit_one net/core/dev.c:3845 [inline]
dev_hard_start_xmit+0x22f/0xa30 net/core/dev.c:3861
__dev_queue_xmit+0x3c51/0x5e60 net/core/dev.c:4763
dev_queue_xmit include/linux/netdevice.h:3365 [inline]
packet_xmit+0x8f/0x710 net/packet/af_packet.c:275
packet_snd net/packet/af_packet.c:3076 [inline]
packet_sendmsg+0x9173/0xa2a0 net/packet/af_packet.c:3108
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x333/0x3d0 net/socket.c:742
__sys_sendto+0x593/0x720 net/socket.c:2244
__do_sys_sendto net/socket.c:2251 [inline]
__se_sys_sendto net/socket.c:2247 [inline]
__x64_sys_sendto+0x130/0x200 net/socket.c:2247
x64_sys_call+0x3924/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:45
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:4962 [inline]
slab_alloc_node mm/slub.c:5265 [inline]
kmem_cache_alloc_node_noprof+0x989/0x16b0 mm/slub.c:5317
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]
alloc_skb_with_frags+0xc5/0xa60 net/core/skbuff.c:6671
sock_alloc_send_pskb+0xacc/0xc60 net/core/sock.c:2965
packet_alloc_skb net/packet/af_packet.c:2926 [inline]
packet_snd net/packet/af_packet.c:3019 [inline]
packet_sendmsg+0x743d/0xa2a0 net/packet/af_packet.c:3108
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x333/0x3d0 net/socket.c:742
__sys_sendto+0x593/0x720 net/socket.c:2244
__do_sys_sendto net/socket.c:2251 [inline]
__se_sys_sendto net/socket.c:2247 [inline]
__x64_sys_sendto+0x130/0x200 net/socket.c:2247
x64_sys_call+0x3924/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:45
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: 6051 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(none)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
=====================================================


---
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***

Subject: Re: [syzbot] [wireless?] KMSAN: uninit-value in cfg80211_classify8021d
Author: lis...@listout.xyz

On 20.10.2025 14:07, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 98ac9cc4b445 Merge tag 'f2fs-fix-6.18-rc2' of git://git.ke..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16be6734580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=bbd3e7f3c2e28265
> dashboard link: https://syzkaller.appspot.com/bug?extid=878ddc3962f792e9af59
> 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=111e7dcd980000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1223a492580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f8ad8459a8da/disk-98ac9cc4.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/28720fa307c1/vmlinux-98ac9cc4.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/e4f310acec99/bzImage-98ac9cc4.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+878ddc...@syzkaller.appspotmail.com

#syz test

diff --git a/net/wireless/util.c b/net/wireless/util.c
index 56724b33af04..b7290912dffb 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -938,9 +938,9 @@ EXPORT_SYMBOL(ieee80211_amsdu_to_8023s);
unsigned int cfg80211_classify8021d(struct sk_buff *skb,
struct cfg80211_qos_map *qos_map)
{
- unsigned int dscp;
- unsigned char vlan_priority;
- unsigned int ret;
+ unsigned int dscp = 0;
+ unsigned char vlan_priority = 0;
+ unsigned int ret = 0;

/* skb->priority values from 256->263 are magic values to
* directly indicate a specific 802.1d priority. This is used

--
Regards,
listout