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

syzbot
2025-12-31T06:02:25Z

Hello,

syzbot found the following issue on:

HEAD commit: 3f0e9c8cefa9 Merge tag 'block-6.19-20251226' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14d784fc580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b3903bdf68407a14
dashboard link: https://syzkaller.appspot.com/bug?extid=619b9ef527f510a57cfc
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=151f1b92580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=144f5022580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7f2d5650d243/disk-3f0e9c8c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/069034860f2d/vmlinux-3f0e9c8c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/90d1c240dc1b/bzImage-3f0e9c8c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+619b9ef527f510a57cfc@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in bpf_prog_test_run_skb+0x3091/0x3200 net/bpf/test_run.c:-1
bpf_prog_test_run_skb+0x3091/0x3200 net/bpf/test_run.c:-1
bpf_prog_test_run+0x5bb/0x9f0 kernel/bpf/syscall.c:4703
__sys_bpf+0x873/0xeb0 kernel/bpf/syscall.c:6182
__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+0xd3/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
pskb_expand_head+0x310/0x15d0 net/core/skbuff.c:2290
__skb_cow include/linux/skbuff.h:3853 [inline]
skb_cow_head include/linux/skbuff.h:3887 [inline]
bpf_skb_net_grow net/core/filter.c:3511 [inline]
____bpf_skb_adjust_room net/core/filter.c:3754 [inline]
bpf_skb_adjust_room+0x103c/0x3310 net/core/filter.c:3699
___bpf_prog_run+0x1297/0xeba0 kernel/bpf/core.c:2037
__bpf_prog_run512+0xc5/0x100 kernel/bpf/core.c:2333
bpf_dispatcher_nop_func include/linux/bpf.h:1378 [inline]
__bpf_prog_run include/linux/filter.h:723 [inline]
bpf_prog_run include/linux/filter.h:730 [inline]
bpf_test_run+0x496/0xe00 net/bpf/test_run.c:423
bpf_prog_test_run_skb+0x2377/0x3200 net/bpf/test_run.c:1158
bpf_prog_test_run+0x5bb/0x9f0 kernel/bpf/syscall.c:4703
__sys_bpf+0x873/0xeb0 kernel/bpf/syscall.c:6182
__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+0xd3/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
skb_data_move+0x424/0x570 include/linux/skbuff.h:-1
skb_postpush_data_move include/linux/skbuff.h:4639 [inline]
bpf_skb_generic_push net/core/filter.c:3267 [inline]
bpf_skb_net_hdr_push net/core/filter.c:3305 [inline]
bpf_skb_net_grow net/core/filter.c:3542 [inline]
____bpf_skb_adjust_room net/core/filter.c:3754 [inline]
bpf_skb_adjust_room+0x116c/0x3310 net/core/filter.c:3699
___bpf_prog_run+0x1297/0xeba0 kernel/bpf/core.c:2037
__bpf_prog_run512+0xc5/0x100 kernel/bpf/core.c:2333
bpf_dispatcher_nop_func include/linux/bpf.h:1378 [inline]
__bpf_prog_run include/linux/filter.h:723 [inline]
bpf_prog_run include/linux/filter.h:730 [inline]
bpf_test_run+0x496/0xe00 net/bpf/test_run.c:423
bpf_prog_test_run_skb+0x2377/0x3200 net/bpf/test_run.c:1158
bpf_prog_test_run+0x5bb/0x9f0 kernel/bpf/syscall.c:4703
__sys_bpf+0x873/0xeb0 kernel/bpf/syscall.c:6182
__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+0xd3/0xf80 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:4960 [inline]
slab_alloc_node mm/slub.c:5263 [inline]
kmem_cache_alloc_node_noprof+0x9e7/0x17a0 mm/slub.c:5315
kmalloc_reserve+0x13c/0x4b0 net/core/skbuff.c:586
pskb_expand_head+0x1fc/0x15d0 net/core/skbuff.c:2282
__skb_cow include/linux/skbuff.h:3853 [inline]
skb_cow_head include/linux/skbuff.h:3887 [inline]
bpf_skb_net_grow net/core/filter.c:3511 [inline]
____bpf_skb_adjust_room net/core/filter.c:3754 [inline]
bpf_skb_adjust_room+0x103c/0x3310 net/core/filter.c:3699
___bpf_prog_run+0x1297/0xeba0 kernel/bpf/core.c:2037
__bpf_prog_run512+0xc5/0x100 kernel/bpf/core.c:2333
bpf_dispatcher_nop_func include/linux/bpf.h:1378 [inline]
__bpf_prog_run include/linux/filter.h:723 [inline]
bpf_prog_run include/linux/filter.h:730 [inline]
bpf_test_run+0x496/0xe00 net/bpf/test_run.c:423
bpf_prog_test_run_skb+0x2377/0x3200 net/bpf/test_run.c:1158
bpf_prog_test_run+0x5bb/0x9f0 kernel/bpf/syscall.c:4703
__sys_bpf+0x873/0xeb0 kernel/bpf/syscall.c:6182
__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+0xd3/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 6072 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(none)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
=====================================================

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