[syzbot] [bpf?] KMSAN: uninit-value in handle_bug

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cc25df3e2e22 Merge tag 'for-6.19/block-20251201' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16c2eab4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6c445efc9db431cb
dashboard link: https://syzkaller.appspot.com/bug?extid=ba80855313e6fa65717a
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a1afac06cfc1/disk-cc25df3e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7bd5369ac00a/vmlinux-cc25df3e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e183dedd04c6/bzImage-cc25df3e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ba8085...@syzkaller.appspotmail.com

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BUG: KMSAN: uninit-value in vsnprintf+0x15d9/0x1b30 lib/vsprintf.c:2911
vsnprintf+0x15d9/0x1b30 lib/vsprintf.c:2911
vprintk_store+0x3ae/0x1530 kernel/printk/printk.c:2255
vprintk_emit+0x27b/0xc50 kernel/printk/printk.c:2402
vprintk_default+0x3f/0x50 kernel/printk/printk.c:2441
vprintk+0x36/0x50 kernel/printk/printk_safe.c:82
__warn_printf lib/bug.c:187 [inline]
__report_bug+0xa53/0xe80 lib/bug.c:240
report_bug_entry+0x148/0x1d0 lib/bug.c:265
handle_bug+0xe1/0x230 arch/x86/kernel/traps.c:430
exc_invalid_op+0x1f/0x50 arch/x86/kernel/traps.c:489
asm_exc_invalid_op+0x1f/0x30 arch/x86/include/asm/idtentry.h:616
reg_bounds_sanity_check+0x577/0x1450 kernel/bpf/verifier.c:2742
reg_set_min_max+0x3be/0x450 kernel/bpf/verifier.c:16572
check_cond_jmp_op+0x3a87/0x5380 kernel/bpf/verifier.c:17016
do_check_insn kernel/bpf/verifier.c:20441 [inline]
do_check+0x23ef/0x16a50 kernel/bpf/verifier.c:20581
do_check_common+0x2217/0x3370 kernel/bpf/verifier.c:23865
do_check_main kernel/bpf/verifier.c:23948 [inline]
bpf_check+0x1e78c/0x27610 kernel/bpf/verifier.c:25255
bpf_prog_load+0x2af6/0x3100 kernel/bpf/syscall.c:3088
__sys_bpf+0x7df/0xeb0 kernel/bpf/syscall.c:6164
__do_sys_bpf kernel/bpf/syscall.c:6274 [inline]
__se_sys_bpf kernel/bpf/syscall.c:6272 [inline]
__x64_sys_bpf+0xa4/0xf0 kernel/bpf/syscall.c:6272
x64_sys_call+0x31c3/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:322
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd9/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
vsnprintf+0x15d2/0x1b30 lib/vsprintf.c:-1
vprintk_store+0x3ae/0x1530 kernel/printk/printk.c:2255
vprintk_emit+0x27b/0xc50 kernel/printk/printk.c:2402
vprintk_default+0x3f/0x50 kernel/printk/printk.c:2441
vprintk+0x36/0x50 kernel/printk/printk_safe.c:82
__warn_printf lib/bug.c:187 [inline]
__report_bug+0xa53/0xe80 lib/bug.c:240
report_bug_entry+0x148/0x1d0 lib/bug.c:265
handle_bug+0xe1/0x230 arch/x86/kernel/traps.c:430
exc_invalid_op+0x1f/0x50 arch/x86/kernel/traps.c:489
asm_exc_invalid_op+0x1f/0x30 arch/x86/include/asm/idtentry.h:616

Local variable run_ctx.i created at:
__bpf_trace_run kernel/trace/bpf_trace.c:2063 [inline]
bpf_trace_run4+0xdf/0x590 kernel/trace/bpf_trace.c:2118
__bpf_trace_sched_switch+0x221/0x290 include/trace/events/sched.h:220

CPU: 1 UID: 0 PID: 23594 Comm: syz.7.5009 Tainted: G W syzkaller #0 PREEMPT(none)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
=====================================================


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