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| author | Jiri Bohac <jbohac@suse.cz> | 2022-01-26 18:00:18 +0300 |
|---|---|---|
| committer | Steffen Klassert <steffen.klassert@secunet.com> | 2022-01-27 09:34:06 +0300 |
| commit | a6d95c5a628a09be129f25d5663a7e9db8261f51 (patch) | |
| tree | 3f6bc5a2ff4abde673736d2d3fd088e6cefb384e /net/ipv4/esp4.c | |
| parent | e03c3bba351f99ad932e8f06baa9da1afc418e02 (diff) | |
| download | linux-a6d95c5a628a09be129f25d5663a7e9db8261f51.tar.xz | |
Revert "xfrm: xfrm_state_mtu should return at least 1280 for ipv6"
This reverts commit b515d2637276a3810d6595e10ab02c13bfd0b63a.
Commit b515d2637276a3810d6595e10ab02c13bfd0b63a ("xfrm: xfrm_state_mtu
should return at least 1280 for ipv6") in v5.14 breaks the TCP MSS
calculation in ipsec transport mode, resulting complete stalls of TCP
connections. This happens when the (P)MTU is 1280 or slighly larger.
The desired formula for the MSS is:
MSS = (MTU - ESP_overhead) - IP header - TCP header
However, the above commit clamps the (MTU - ESP_overhead) to a
minimum of 1280, turning the formula into
MSS = max(MTU - ESP overhead, 1280) - IP header - TCP header
With the (P)MTU near 1280, the calculated MSS is too large and the
resulting TCP packets never make it to the destination because they
are over the actual PMTU.
The above commit also causes suboptimal double fragmentation in
xfrm tunnel mode, as described in
https://lore.kernel.org/netdev/20210429202529.codhwpc7w6kbudug@dwarf.suse.cz/
The original problem the above commit was trying to fix is now fixed
by commit 6596a0229541270fb8d38d989f91b78838e5e9da ("xfrm: fix MTU
regression").
Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Diffstat (limited to 'net/ipv4/esp4.c')
| -rw-r--r-- | net/ipv4/esp4.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c index 851f542928a3..e1b1d080e908 100644 --- a/net/ipv4/esp4.c +++ b/net/ipv4/esp4.c @@ -671,7 +671,7 @@ static int esp_output(struct xfrm_state *x, struct sk_buff *skb) struct xfrm_dst *dst = (struct xfrm_dst *)skb_dst(skb); u32 padto; - padto = min(x->tfcpad, __xfrm_state_mtu(x, dst->child_mtu_cached)); + padto = min(x->tfcpad, xfrm_state_mtu(x, dst->child_mtu_cached)); if (skb->len < padto) esp.tfclen = padto - skb->len; } |