Patch "gso: fix dodgy bit handling for GSO_UDP_L4" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    gso: fix dodgy bit handling for GSO_UDP_L4

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     gso-fix-dodgy-bit-handling-for-gso_udp_l4.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 6090361de3c7650680b9a2b098828072864fe334
Author: Yan Zhai <yan@xxxxxxxxxxxxxx>
Date:   Thu Jul 13 10:28:00 2023 -0700

    gso: fix dodgy bit handling for GSO_UDP_L4
    
    [ Upstream commit 9840036786d90cea11a90d1f30b6dc003b34ee67 ]
    
    Commit 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4
    packets.") checks DODGY bit for UDP, but for packets that can be fed
    directly to the device after gso_segs reset, it actually falls through
    to fragmentation:
    
    https://lore.kernel.org/all/CAJPywTKDdjtwkLVUW6LRA2FU912qcDmQOQGt2WaDo28KzYDg+A@xxxxxxxxxxxxxx/
    
    This change restores the expected behavior of GSO_UDP_L4 packets.
    
    Fixes: 1fd54773c267 ("udp: allow header check for dodgy GSO_UDP_L4 packets.")
    Suggested-by: Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx>
    Signed-off-by: Yan Zhai <yan@xxxxxxxxxxxxxx>
    Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>
    Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 1f01e15ca24fd..4a61832e7f69b 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -273,13 +273,20 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
 	__sum16 check;
 	__be16 newlen;
 
-	if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST)
-		return __udp_gso_segment_list(gso_skb, features, is_ipv6);
-
 	mss = skb_shinfo(gso_skb)->gso_size;
 	if (gso_skb->len <= sizeof(*uh) + mss)
 		return ERR_PTR(-EINVAL);
 
+	if (skb_gso_ok(gso_skb, features | NETIF_F_GSO_ROBUST)) {
+		/* Packet is from an untrusted source, reset gso_segs. */
+		skb_shinfo(gso_skb)->gso_segs = DIV_ROUND_UP(gso_skb->len - sizeof(*uh),
+							     mss);
+		return NULL;
+	}
+
+	if (skb_shinfo(gso_skb)->gso_type & SKB_GSO_FRAGLIST)
+		return __udp_gso_segment_list(gso_skb, features, is_ipv6);
+
 	skb_pull(gso_skb, sizeof(*uh));
 
 	/* clear destructor to avoid skb_segment assigning it to tail */
@@ -387,8 +394,7 @@ static struct sk_buff *udp4_ufo_fragment(struct sk_buff *skb,
 	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 		goto out;
 
-	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4 &&
-	    !skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST))
+	if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
 		return __udp_gso_segment(skb, features, false);
 
 	mss = skb_shinfo(skb)->gso_size;
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index c39c1e32f9804..e0e10f6bcdc18 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -42,8 +42,7 @@ static struct sk_buff *udp6_ufo_fragment(struct sk_buff *skb,
 		if (!pskb_may_pull(skb, sizeof(struct udphdr)))
 			goto out;
 
-		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4 &&
-		    !skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST))
+		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4)
 			return __udp_gso_segment(skb, features, true);
 
 		mss = skb_shinfo(skb)->gso_size;