linux-kernel - [PATCH] net: skbuff: fix uninitialized memory use in pskb_expand

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Message-Id: <20260114135643.17484-1-sohammetha01@gmail.com>
Date: Wed, 14 Jan 2026 19:26:43 +0530
From: Soham Metha <sohammetha01@...il.com>
To: linux-kernel-mentees@...ts.linuxfoundation.org
Cc: shuah@...nel.org,
	syzbot+619b9ef527f510a57cfc@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com,
	andrii@...nel.org,
	ast@...nel.org,
	bpf@...r.kernel.org,
	daniel@...earbox.net,
	eddyz87@...il.com,
	haoluo@...gle.com,
	john.fastabend@...il.com,
	jolsa@...nel.org,
	kpsingh@...nel.org,
	linux-kernel@...r.kernel.org,
	martin.lau@...ux.dev,
	sdf@...ichev.me,
	song@...nel.org,
	yonghong.song@...ux.dev,
	Soham Metha <sohammetha01@...il.com>
Subject: [PATCH] net: skbuff: fix uninitialized memory use in pskb_expand_head()

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@...kaller.appspotmail.com
Signed-off-by: Soham Metha <sohammetha01@...il.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