Revert "bpf: Check for BPF_F_ADJ_ROOM_FIXED_GSO when bpf_skb_change_proto"

This reverts commit fa7b83bf3b156c767f3e4a25bbf3817b08f3ff8e.

See the followup commit for the reasoning why I believe the appropriate
approach is to simply make this change without a flag, but it can basically
be summarized as using this helper without the flag is bug-prone or outright
buggy, and thus the default should be this new behaviour.

As this commit has only made it into net-next/master, but not into
any real release, such a backwards incompatible change is still ok.

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/20210617000953.2787453-1-zenczykowski@gmail.com

diff --git a/net/core/filter.c b/net/core/filter.c
index 0b13d8157a8fbdde3e01633a73b118e5b8dd16a9..243abf519efda38b4f641d86677c61f80da237bf 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3235,7 +3235,7 @@ static int bpf_skb_net_hdr_pop(struct sk_buff *skb, u32 off, u32 len)
        return ret;
 }
 
-static int bpf_skb_proto_4_to_6(struct sk_buff *skb, u64 flags)
+static int bpf_skb_proto_4_to_6(struct sk_buff *skb)
 {
        const u32 len_diff = sizeof(struct ipv6hdr) - sizeof(struct iphdr);
        u32 off = skb_mac_header_len(skb);
@@ -3264,9 +3264,7 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb, u64 flags)
                }
 
                /* Due to IPv6 header, MSS needs to be downgraded. */
-               if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO))
-                       skb_decrease_gso_size(shinfo, len_diff);
-
+               skb_decrease_gso_size(shinfo, len_diff);
                /* Header must be checked, and gso_segs recomputed. */
                shinfo->gso_type |= SKB_GSO_DODGY;
                shinfo->gso_segs = 0;
@@ -3278,7 +3276,7 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb, u64 flags)
        return 0;
 }
 
-static int bpf_skb_proto_6_to_4(struct sk_buff *skb, u64 flags)
+static int bpf_skb_proto_6_to_4(struct sk_buff *skb)
 {
        const u32 len_diff = sizeof(struct ipv6hdr) - sizeof(struct iphdr);
        u32 off = skb_mac_header_len(skb);
@@ -3307,9 +3305,7 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb, u64 flags)
                }
 
                /* Due to IPv4 header, MSS can be upgraded. */
-               if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO))
-                       skb_increase_gso_size(shinfo, len_diff);
-
+               skb_increase_gso_size(shinfo, len_diff);
                /* Header must be checked, and gso_segs recomputed. */
                shinfo->gso_type |= SKB_GSO_DODGY;
                shinfo->gso_segs = 0;
@@ -3321,17 +3317,17 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb, u64 flags)
        return 0;
 }
 
-static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto, u64 flags)
+static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto)
 {
        __be16 from_proto = skb->protocol;
 
        if (from_proto == htons(ETH_P_IP) &&
              to_proto == htons(ETH_P_IPV6))
-               return bpf_skb_proto_4_to_6(skb, flags);
+               return bpf_skb_proto_4_to_6(skb);
 
        if (from_proto == htons(ETH_P_IPV6) &&
              to_proto == htons(ETH_P_IP))
-               return bpf_skb_proto_6_to_4(skb, flags);
+               return bpf_skb_proto_6_to_4(skb);
 
        return -ENOTSUPP;
 }
@@ -3341,7 +3337,7 @@ BPF_CALL_3(bpf_skb_change_proto, struct sk_buff *, skb, __be16, proto,
 {
        int ret;
 
-       if (unlikely(flags & ~(BPF_F_ADJ_ROOM_FIXED_GSO)))
+       if (unlikely(flags))
                return -EINVAL;
 
        /* General idea is that this helper does the basic groundwork
@@ -3361,7 +3357,7 @@ BPF_CALL_3(bpf_skb_change_proto, struct sk_buff *, skb, __be16, proto,
         * that. For offloads, we mark packet as dodgy, so that headers
         * need to be verified first.
         */
-       ret = bpf_skb_proto_xlat(skb, proto, flags);
+       ret = bpf_skb_proto_xlat(skb, proto);
        bpf_compute_data_pointers(skb);
        return ret;
 }