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* [PATCH] net: skbuff: fix uninitialized memory use in pskb_expand_head()
  2025-12-31  6:02 syzbot
@ 2026-01-14 13:56 Soham Metha
  2026-01-14 15:06 ` [syzbot] [bpf?] KMSAN: uninit-value in bpf_prog_test_run_skb syzbot
  -1 siblings, 1 reply; 9+ messages in thread
From: Soham Metha @ 2026-01-14 13:56 UTC (permalink / raw)
  To: linux-kernel-mentees
  Cc: shuah, syzbot+619b9ef527f510a57cfc, syzkaller-bugs, andrii, ast,
	bpf, daniel, eddyz87, haoluo, john.fastabend, jolsa, kpsingh,
	linux-kernel, martin.lau, sdf, song, yonghong.song, Soham Metha

pskb_expand_head() allocates a new skb data buffer using
kmalloc_reserve(), which does not initialize memory. skb helpers may
later copy or move padding bytes from the buffer.

Initialize the newly allocated skb buffer to avoid propagating
uninitialized memory.

Reported-by: syzbot+619b9ef527f510a57cfc@syzkaller.appspotmail.com
Signed-off-by: Soham Metha <sohammetha01@gmail.com>
---
#syz test

 net/core/skbuff.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a56133902c0d..b0f0d3a0310b 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2282,6 +2282,9 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 	data = kmalloc_reserve(&size, gfp_mask, NUMA_NO_NODE, NULL);
 	if (!data)
 		goto nodata;
+
+	memset(data, 0, size);
+
 	size = SKB_WITH_OVERHEAD(size);
 
 	/* Copy only real data... and, alas, header. This should be
-- 
2.34.1


^ permalink raw reply related	[flat|nested] 9+ messages in thread
[parent not found: <20260114123333.13206-1-sohammetha01@gmail.com>]
[parent not found: <20260114120911.9472-1-sohammetha01@gmail.com>]
[parent not found: <20260104034826.7723-1-kartikey406@gmail.com>]
[parent not found: <20260104020145.4942-1-kartikey406@gmail.com>]
[parent not found: <20260102021954.297351-1-kartikey406@gmail.com>]
* [syzbot] [bpf?] KMSAN: uninit-value in bpf_prog_test_run_skb
@ 2025-12-31  6:02 syzbot
  0 siblings, 0 replies; 9+ messages in thread
From: syzbot @ 2025-12-31  6:02 UTC (permalink / raw)
  To: andrii, ast, bpf, daniel, eddyz87, haoluo, john.fastabend, jolsa,
	kpsingh, linux-kernel, martin.lau, sdf, song, syzkaller-bugs,
	yonghong.song

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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^ permalink raw reply	[flat|nested] 9+ messages in thread
end of thread, other threads:[~2026-03-30  3:45 UTC | newest]

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2026-01-04  6:12 ` [syzbot] [bpf?] KMSAN: uninit-value in bpf_prog_test_run_skb syzbot
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2026-03-30  3:45 ` syzbot
2026-01-14 13:56 [PATCH] net: skbuff: fix uninitialized memory use in pskb_expand_head() Soham Metha
2026-01-14 15:06 ` [syzbot] [bpf?] KMSAN: uninit-value in bpf_prog_test_run_skb syzbot
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