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bpf: Check for BPF_F_ADJ_ROOM_FIXED_GSO when bpf_skb_change_proto

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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@samsung.com
This commit is contained in:
Dongseok Yi 2021-05-12 16:27:33 +09:00 committed by Daniel Borkmann
parent c49661aa6f
commit fa7b83bf3b
1 changed files with 13 additions and 9 deletions
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22
net/core/filter.c
View File

@ -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)
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);
@ -3264,7 +3264,9 @@ 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;
@ -3276,7 +3278,7 @@ 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);
@ -3305,7 +3307,9 @@ 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;
@ -3317,17 +3321,17 @@ 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;
}
@ -3337,7 +3341,7 @@ 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
@ -3357,7 +3361,7 @@ 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;
}