Hello,

syzbot found the following issue on:

HEAD commit:    ca4ee40bf13d Partly revert "drm/hyperv: Remove reference t..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=175d1b3a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4b4f2aab682301f1
dashboard link: https://syzkaller.appspot.com/bug?extid=b09c1af8764c0097bb19
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/5f321eee08a1/disk-ca4ee40b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e93195c44eb5/vmlinux-ca4ee40b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c3f7091036e0/bzImage-ca4ee40b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b09c1af8764c0097bb19@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in ieee80211_radiotap_iterator_next+0x11f8/0x1620 net/wireless/radiotap.c:317
 ieee80211_radiotap_iterator_next+0x11f8/0x1620 net/wireless/radiotap.c:317
 ieee80211_parse_tx_radiotap+0x4bb/0x2160 net/mac80211/tx.c:2122
 ieee80211_monitor_start_xmit+0x125e/0x1750 net/mac80211/tx.c:2451
 __netdev_start_xmit include/linux/netdevice.h:5275 [inline]
 netdev_start_xmit include/linux/netdevice.h:5284 [inline]
 xmit_one net/core/dev.c:3864 [inline]
 dev_hard_start_xmit+0x24e/0xad0 net/core/dev.c:3880
 __dev_queue_xmit+0x35e0/0x5a50 net/core/dev.c:4829
 dev_queue_xmit include/linux/netdevice.h:3384 [inline]
 packet_xmit+0x8f/0x710 net/packet/af_packet.c:275
 packet_snd net/packet/af_packet.c:3077 [inline]
 packet_sendmsg+0x91d9/0xa320 net/packet/af_packet.c:3109
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg net/socket.c:742 [inline]
 __sys_sendto+0xa77/0xb90 net/socket.c:2206
 __do_sys_sendto net/socket.c:2213 [inline]
 __se_sys_sendto net/socket.c:2209 [inline]
 __ia32_sys_sendto+0x12f/0x200 net/socket.c:2209
 ia32_sys_call+0x372f/0x4360 arch/x86/include/generated/asm/syscalls_32.h:370
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x17f/0x3f0 arch/x86/entry/syscall_32.c:307
 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

Uninit was stored to memory at:
 ieee80211_radiotap_iterator_next+0x14c8/0x1620 net/wireless/radiotap.c:251
 ieee80211_parse_tx_radiotap+0x4bb/0x2160 net/mac80211/tx.c:2122
 ieee80211_monitor_start_xmit+0x125e/0x1750 net/mac80211/tx.c:2451
 __netdev_start_xmit include/linux/netdevice.h:5275 [inline]
 netdev_start_xmit include/linux/netdevice.h:5284 [inline]
 xmit_one net/core/dev.c:3864 [inline]
 dev_hard_start_xmit+0x24e/0xad0 net/core/dev.c:3880
 __dev_queue_xmit+0x35e0/0x5a50 net/core/dev.c:4829
 dev_queue_xmit include/linux/netdevice.h:3384 [inline]
 packet_xmit+0x8f/0x710 net/packet/af_packet.c:275
 packet_snd net/packet/af_packet.c:3077 [inline]
 packet_sendmsg+0x91d9/0xa320 net/packet/af_packet.c:3109
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg net/socket.c:742 [inline]
 __sys_sendto+0xa77/0xb90 net/socket.c:2206
 __do_sys_sendto net/socket.c:2213 [inline]
 __se_sys_sendto net/socket.c:2209 [inline]
 __ia32_sys_sendto+0x12f/0x200 net/socket.c:2209
 ia32_sys_call+0x372f/0x4360 arch/x86/include/generated/asm/syscalls_32.h:370
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x17f/0x3f0 arch/x86/entry/syscall_32.c:307
 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 iterator created at:
 ieee80211_parse_tx_radiotap+0xc4/0x2160 net/mac80211/tx.c:2093
 ieee80211_monitor_start_xmit+0x125e/0x1750 net/mac80211/tx.c:2451

CPU: 1 UID: 0 PID: 12634 Comm: syz.4.1919 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================


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