[PATCH AUTOSEL 5.12 026/160] bpf: Check for BPF_F_ADJ_ROOM_FIXED_GSO when bpf_skb_change_proto
From: Sasha Levin <sashal@kernel.org>
Date: 2021-07-06 11:30:05
Also in:
bpf, lkml, netdev
Subsystem:
bpf [general] (safe dynamic programs and tools), bpf [networking] (tcx & tc bpf, sock_addr), networking [general], the rest · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Dongseok Yi <redacted>
[ 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 <redacted>
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@samsung.com (local)
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 52f4359efbd2..849b08350a39 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c@@ -3238,7 +3238,7 @@ 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);
@@ -3267,7 +3267,9 @@ 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;
@@ -3279,7 +3281,7 @@ 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);
@@ -3308,7 +3310,9 @@ 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;
@@ -3320,17 +3324,17 @@ 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; }
@@ -3340,7 +3344,7 @@ 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
@@ -3360,7 +3364,7 @@ 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; }
--
2.30.2