[PATCH net-next v2 7/8] net: skbuff: don't BUG() on a missing head_frag in skb_zerocopy()

[Josef Bacik <josef@toxicpanda.com>]

skb_zerocopy() BUG()s if @from has no head_frag and the caller passed
hlen == 0, meaning the caller didn't ask for the head to be copied and
the head can't be referenced as a page either.  The check runs before
anything is touched, and skb_zerocopy() already documents -EFAULT for
bad skb geometry.  Return that, with a DEBUG_NET_WARN_ON_ONCE() for
debug kernels.

Assisted-by: LLM
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 net/core/skbuff.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7fd2f8142cc4..629de22d98e4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3913,7 +3913,10 @@ skb_zerocopy(struct sk_buff *to, struct sk_buff *from, int len, int hlen)
 	struct page *page;
 	unsigned int offset;
 
-	BUG_ON(!from->head_frag && !hlen);
+	if (unlikely(!from->head_frag && !hlen)) {
+		DEBUG_NET_WARN_ON_ONCE(1);
+		return -EFAULT;
+	}
 
 	/* dont bother with small payloads */
 	if (len <= skb_tailroom(to))

-- 
2.55.0