[syzbot] [net?] KMSAN: uninit-value in unwind_dump

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0bbac3facb5d Linux 6.9-rc4
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13403bcb180000
kernel config: https://syzkaller.appspot.com/x/.config?x=87a805e655619c64
dashboard link: https://syzkaller.appspot.com/bug?extid=355c5bb8c1445c871ee8
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/93eb2bab28b5/disk-0bbac3fa.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/47a883d2dfaa/vmlinux-0bbac3fa.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6bc56900ec1d/bzImage-0bbac3fa.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+355c5b...@syzkaller.appspotmail.com

WARNING: kernel stack frame pointer at ffff88813fd05fe8 in kworker/1:1:42 has bad value ffff888103513fe8
unwind stack type:0 next_sp:ffff888103513fd8 mask:0x4 graph_idx:0
=====================================================
BUG: KMSAN: uninit-value in unwind_dump+0x5a0/0x730 arch/x86/kernel/unwind_frame.c:60
unwind_dump+0x5a0/0x730 arch/x86/kernel/unwind_frame.c:60
unwind_next_frame+0x2d6/0x470
arch_stack_walk+0x1ec/0x2d0 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0xaa/0xe0 kernel/stacktrace.c:122
ref_tracker_free+0x103/0xec0 lib/ref_tracker.c:239
__netns_tracker_free include/net/net_namespace.h:348 [inline]
put_net_track include/net/net_namespace.h:363 [inline]
__sk_destruct+0x5aa/0xb70 net/core/sock.c:2204
sk_destruct net/core/sock.c:2223 [inline]
__sk_free+0x6de/0x760 net/core/sock.c:2234
sk_free+0x70/0xc0 net/core/sock.c:2245
deferred_put_nlk_sk+0x243/0x270 net/netlink/af_netlink.c:744
rcu_do_batch kernel/rcu/tree.c:2196 [inline]
rcu_core+0xa59/0x1e70 kernel/rcu/tree.c:2471
rcu_core_si+0x12/0x20 kernel/rcu/tree.c:2488
__do_softirq+0x1c0/0x7d7 kernel/softirq.c:554
invoke_softirq kernel/softirq.c:428 [inline]
__irq_exit_rcu kernel/softirq.c:633 [inline]
irq_exit_rcu+0x6a/0x130 kernel/softirq.c:645
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
sysvec_apic_timer_interrupt+0x83/0x90 arch/x86/kernel/apic/apic.c:1043

Local variable tx created at:
ieee80211_get_buffered_bc+0x44/0x970 net/mac80211/tx.c:5886
mac80211_hwsim_beacon_tx+0x63b/0xb40 drivers/net/wireless/virtual/mac80211_hwsim.c:2303

CPU: 1 PID: 42 Comm: kworker/1:1 Not tainted 6.9.0-rc4-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: usb_hub_wq hub_event
=====================================================


---
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 syzk...@googlegroups.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 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

[Alexander Potapenko]

This seems to be a false positive caused by KMSAN instrumenting
READ_ONCE_NOCHECK(), although it is not supposed to.
I was going to define it as follows under __SANITIZE_MEMORY__:

#define __no_sanitize_or_inline __no_kmsan_checks notrace __maybe_unused

, but I find the name __no_sanitize_or_inline a bit unfortunate
because it doesn't distinguish between "do not instrument this code"
and "do not report bugs in this code", which have different meanings
from KMSAN perspective.