[PATCH] Fix KMSAN infoleak, initialize unused data in pskb_expand_head

[Daniel Yang]

pskb_expand_head doesn't initialize extra nhead bytes in header and
tail bytes, leading to KMSAN infoleak error. Fix by initializing data to
0 with memset.

Reported-by: syzbot+346474e3bf0b26bd3090@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: Daniel Yang <danielyangkang@xxxxxxxxx>
Signed-off-by: Daniel Yang <danielyangkang@xxxxxxxxx>
---
 net/core/skbuff.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 74149dc4e..348161dcb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2286,6 +2286,11 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 	       skb_shinfo(skb),
 	       offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));
 
+	/* Initialize newly allocated headroom and tailroom
+	 */
+	memset(data, 0, nhead);
+	memset(data + nhead + skb->tail, 0, skb_tailroom(skb) + ntail);
+
 	/*
 	 * if shinfo is shared we must drop the old head gracefully, but if it
 	 * is not we can just drop the old head and let the existing refcount
-- 
2.39.2