net: core: reject skb_copy(_expand) for fraglist GSO skbs

SKB_GSO_FRAGLIST skbs must not be linearized, otherwise they become
invalid. Return NULL if such an skb is passed to skb_copy or
skb_copy_expand, in order to prevent a crash on a potential later
call to skb_gso_segment.

Fixes: 3a1296a ("net: Support GRO/GSO fraglist chaining.")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: nbd168

net/core/skbuff.c

@@ -2123,11 +2123,17 @@ static inline int skb_alloc_rx_flag(const struct sk_buff *skb)
 
 struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
 {
-	int headerlen = skb_headroom(skb);
-	unsigned int size = skb_end_offset(skb) + skb->data_len;
-	struct sk_buff *n = __alloc_skb(size, gfp_mask,
-					skb_alloc_rx_flag(skb), NUMA_NO_NODE);
+	struct sk_buff *n;
+	unsigned int size;
+	int headerlen;
+
+	if (WARN_ON_ONCE(skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST))
+		return NULL;
 
+	headerlen = skb_headroom(skb);
+	size = skb_end_offset(skb) + skb->data_len;
+	n = __alloc_skb(size, gfp_mask,
+			skb_alloc_rx_flag(skb), NUMA_NO_NODE);
 	if (!n)
 		return NULL;
 
@@ -2455,12 +2461,17 @@ struct sk_buff *skb_copy_expand(const struct sk_buff *skb,
 	/*
 	 *	Allocate the copy buffer
 	 */
-	struct sk_buff *n = __alloc_skb(newheadroom + skb->len + newtailroom,
-					gfp_mask, skb_alloc_rx_flag(skb),
-					NUMA_NO_NODE);
-	int oldheadroom = skb_headroom(skb);
 	int head_copy_len, head_copy_off;
+	struct sk_buff *n;
+	int oldheadroom;
+
+	if (WARN_ON_ONCE(skb_shinfo(skb)->gso_type & SKB_GSO_FRAGLIST))
+		return NULL;
 
+	oldheadroom = skb_headroom(skb);
+	n = __alloc_skb(newheadroom + skb->len + newtailroom,
+			gfp_mask, skb_alloc_rx_flag(skb),
+			NUMA_NO_NODE);
 	if (!n)
 		return NULL;