[PATCH net-next v2 3/8] net: skbuff: don't BUG() when skb_copy_bits() fails in copy helpers

[Josef Bacik <josef@toxicpanda.com>]

skb_copy(), skb_copy_expand() and skb_try_coalesce() all BUG() if
skb_copy_bits() fails.  skb_copy_bits() only fails when the skb's
lengths don't add up, which is a bug somewhere else, usually in a
driver building the skb.

Each of these functions already has a failure return its callers handle:

 - skb_copy() and skb_copy_expand() free the new skb and return NULL,
   as they do when the allocation fails.
 - skb_try_coalesce() returns false and the caller keeps the skbs
   separate.  Copy into the tailroom before skb_put() so that @to is
   untouched on failure.

Take those returns, with a DEBUG_NET_WARN_ON_ONCE() for debug kernels.

__pskb_pull_tail() has the same BUG_ON(), but several of its callers
can't otherwise fail and don't check its return, so it's left for a
separate change that fixes them first.

Assisted-by: LLM
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 net/core/skbuff.c | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index a6821ab13969..ffc78b1a8ab8 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2201,7 +2201,12 @@ struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
 	/* Set the tail pointer and length */
 	skb_put(n, skb->len);
 
-	BUG_ON(skb_copy_bits(skb, -headerlen, n->head, headerlen + skb->len));
+	if (unlikely(skb_copy_bits(skb, -headerlen, n->head,
+				   headerlen + skb->len))) {
+		DEBUG_NET_WARN_ON_ONCE(1);
+		kfree_skb(n);
+		return NULL;
+	}
 
 	skb_copy_header(n, skb);
 	return n;
@@ -2545,8 +2550,13 @@ struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
 		head_copy_off = newheadroom - head_copy_len;
 
 	/* Copy the linear header and data. */
-	BUG_ON(skb_copy_bits(skb, -head_copy_len, n->head + head_copy_off,
-			     skb->len + head_copy_len));
+	if (unlikely(skb_copy_bits(skb, -head_copy_len,
+				   n->head + head_copy_off,
+				   skb->len + head_copy_len))) {
+		DEBUG_NET_WARN_ON_ONCE(1);
+		kfree_skb(n);
+		return NULL;
+	}
 
 	skb_copy_header(n, skb);
 
@@ -6233,8 +6243,15 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
 		return false;
 
 	if (len <= skb_tailroom(to) && skb_frags_readable(from)) {
-		if (len)
-			BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));
+		if (len) {
+			if (unlikely(skb_copy_bits(from, 0,
+						   skb_tail_pointer(to),
+						   len))) {
+				DEBUG_NET_WARN_ON_ONCE(1);
+				return false;
+			}
+			skb_put(to, len);
+		}
 		*delta_truesize = 0;
 		return true;
 	}

-- 
2.55.0