[PATCH 6.1.y 1/2] net: add skb_header_pointer_careful() helper

[Bin Lan <lanbincn@139.com>]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 13e00fdc9236bd4d0bff4109d2983171fbcb74c4 ]

This variant of skb_header_pointer() should be used in contexts
where @offset argument is user-controlled and could be negative.

Negative offsets are supported, as long as the zone starts
between skb->head and skb->data.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260128141539.3404400-2-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Adjust context ]
Signed-off-by: Bin Lan <lanbincn@139.com>
---
 include/linux/skbuff.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9a04a188b9f8..d07517a29cc1 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4081,6 +4081,18 @@ skb_header_pointer(const struct sk_buff *skb, int offset, int len, void *buffer)
 				    skb_headlen(skb), buffer);
 }
 
+/* Variant of skb_header_pointer() where @offset is user-controlled
+ * and potentially negative.
+ */
+static inline void * __must_check
+skb_header_pointer_careful(const struct sk_buff *skb, int offset,
+			   int len, void *buffer)
+{
+	if (unlikely(offset < 0 && -offset > skb_headroom(skb)))
+		return NULL;
+	return skb_header_pointer(skb, offset, len, buffer);
+}
+
 /**
  *	skb_needs_linearize - check if we need to linearize a given skb
  *			      depending on the given device features.
-- 
2.43.0