bpf: Support all gso types in bpf_skb_change_proto()

Since we no longer modify gso_size, it is now theoretically
safe to not set SKB_GSO_DODGY and reset gso_segs to zero.

This also means the skb_is_gso_tcp() check should no longer
be necessary.

Unfortunately we cannot remove the skb_{decrease,increase}_gso_size()
helpers, as they are still used elsewhere:

  bpf_skb_net_grow() without BPF_F_ADJ_ROOM_FIXED_GSO
  bpf_skb_net_shrink() without BPF_F_ADJ_ROOM_FIXED_GSO
  net/core/lwt_bpf.c's handle_gso_type()

Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Dongseok Yi <dseok.yi@samsung.com>
Cc: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/bpf/20210617000953.2787453-3-zenczykowski@gmail.com

diff --git a/net/core/filter.c b/net/core/filter.c
index ae92a8b..d062053 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3241,9 +3241,6 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb)
        u32 off = skb_mac_header_len(skb);
        int ret;
 
-       if (skb_is_gso(skb) && !skb_is_gso_tcp(skb))
-               return -ENOTSUPP;
-
        ret = skb_cow(skb, len_diff);
        if (unlikely(ret < 0))
                return ret;
@@ -3255,17 +3252,11 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb)
        if (skb_is_gso(skb)) {
                struct skb_shared_info *shinfo = skb_shinfo(skb);
 
-               /* SKB_GSO_TCPV4 needs to be changed into
-                * SKB_GSO_TCPV6.
-                */
+               /* SKB_GSO_TCPV4 needs to be changed into SKB_GSO_TCPV6. */
                if (shinfo->gso_type & SKB_GSO_TCPV4) {
                        shinfo->gso_type &= ~SKB_GSO_TCPV4;
                        shinfo->gso_type |=  SKB_GSO_TCPV6;
                }
-
-               /* Header must be checked, and gso_segs recomputed. */
-               shinfo->gso_type |= SKB_GSO_DODGY;
-               shinfo->gso_segs = 0;
        }
 
        skb->protocol = htons(ETH_P_IPV6);
@@ -3280,9 +3271,6 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb)
        u32 off = skb_mac_header_len(skb);
        int ret;
 
-       if (skb_is_gso(skb) && !skb_is_gso_tcp(skb))
-               return -ENOTSUPP;
-
        ret = skb_unclone(skb, GFP_ATOMIC);
        if (unlikely(ret < 0))
                return ret;
@@ -3294,17 +3282,11 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb)
        if (skb_is_gso(skb)) {
                struct skb_shared_info *shinfo = skb_shinfo(skb);
 
-               /* SKB_GSO_TCPV6 needs to be changed into
-                * SKB_GSO_TCPV4.
-                */
+               /* SKB_GSO_TCPV6 needs to be changed into SKB_GSO_TCPV4. */
                if (shinfo->gso_type & SKB_GSO_TCPV6) {
                        shinfo->gso_type &= ~SKB_GSO_TCPV6;
                        shinfo->gso_type |=  SKB_GSO_TCPV4;
                }
-
-               /* Header must be checked, and gso_segs recomputed. */
-               shinfo->gso_type |= SKB_GSO_DODGY;
-               shinfo->gso_segs = 0;
        }
 
        skb->protocol = htons(ETH_P_IP);