From: Dongseok Yi dseok.yi@samsung.com
[ Upstream commit fa7b83bf3b156c767f3e4a25bbf3817b08f3ff8e ]
In the forwarding path GRO -> BPF 6 to 4 -> GSO for TCP traffic, the coalesced packet payload can be > MSS, but < MSS + 20.
bpf_skb_proto_6_to_4() will upgrade the MSS and it can be > the payload length. After then tcp_gso_segment checks for the payload length if it is <= MSS. The condition is causing the packet to be dropped.
tcp_gso_segment(): [...] mss = skb_shinfo(skb)->gso_size; if (unlikely(skb->len <= mss)) goto out; [...]
Allow to upgrade/downgrade MSS only when BPF_F_ADJ_ROOM_FIXED_GSO is not set.
Signed-off-by: Dongseok Yi dseok.yi@samsung.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net Acked-by: Willem de Bruijn willemb@google.com Link: https://lore.kernel.org/bpf/1620804453-57566-1-git-send-email-dseok.yi@samsu... Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/filter.c | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c index 108bcf600052..823e77846525 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2833,7 +2833,7 @@ 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) +static int bpf_skb_proto_4_to_6(struct sk_buff *skb, u64 flags) { const u32 len_diff = sizeof(struct ipv6hdr) - sizeof(struct iphdr); u32 off = skb_mac_header_len(skb); @@ -2862,7 +2862,9 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb) }
/* Due to IPv6 header, MSS needs to be downgraded. */ - skb_decrease_gso_size(shinfo, len_diff); + if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO)) + 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; @@ -2874,7 +2876,7 @@ static int bpf_skb_proto_4_to_6(struct sk_buff *skb) return 0; }
-static int bpf_skb_proto_6_to_4(struct sk_buff *skb) +static int bpf_skb_proto_6_to_4(struct sk_buff *skb, u64 flags) { const u32 len_diff = sizeof(struct ipv6hdr) - sizeof(struct iphdr); u32 off = skb_mac_header_len(skb); @@ -2903,7 +2905,9 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb) }
/* Due to IPv4 header, MSS can be upgraded. */ - skb_increase_gso_size(shinfo, len_diff); + if (!(flags & BPF_F_ADJ_ROOM_FIXED_GSO)) + 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; @@ -2915,17 +2919,17 @@ static int bpf_skb_proto_6_to_4(struct sk_buff *skb) return 0; }
-static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto) +static int bpf_skb_proto_xlat(struct sk_buff *skb, __be16 to_proto, u64 flags) { __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); + return bpf_skb_proto_4_to_6(skb, flags);
if (from_proto == htons(ETH_P_IPV6) && to_proto == htons(ETH_P_IP)) - return bpf_skb_proto_6_to_4(skb); + return bpf_skb_proto_6_to_4(skb, flags);
return -ENOTSUPP; } @@ -2935,7 +2939,7 @@ BPF_CALL_3(bpf_skb_change_proto, struct sk_buff *, skb, __be16, proto, { int ret;
- if (unlikely(flags)) + if (unlikely(flags & ~(BPF_F_ADJ_ROOM_FIXED_GSO))) return -EINVAL;
/* General idea is that this helper does the basic groundwork @@ -2955,7 +2959,7 @@ 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); + ret = bpf_skb_proto_xlat(skb, proto, flags); bpf_compute_data_pointers(skb); return ret; }