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[1/6] xfrm: fix MTU regression

Message ID 20220225074733.118664-2-steffen.klassert@secunet.com (mailing list archive)
State Accepted
Commit 6596a0229541270fb8d38d989f91b78838e5e9da
Delegated to: Netdev Maintainers
Headers show
Series [1/6] xfrm: fix MTU regression | expand

Commit Message

Steffen Klassert Feb. 25, 2022, 7:47 a.m. UTC 
From: Jiri Bohac <jbohac@suse.cz>

Commit 749439bfac6e1a2932c582e2699f91d329658196 ("ipv6: fix udpv6
sendmsg crash caused by too small MTU") breaks PMTU for xfrm.

A Packet Too Big ICMPv6 message received in response to an ESP
packet will prevent all further communication through the tunnel
if the reported MTU minus the ESP overhead is smaller than 1280.

E.g. in a case of a tunnel-mode ESP with sha256/aes the overhead
is 92 bytes. Receiving a PTB with MTU of 1371 or less will result
in all further packets in the tunnel dropped. A ping through the
tunnel fails with "ping: sendmsg: Invalid argument".

Apparently the MTU on the xfrm route is smaller than 1280 and
fails the check inside ip6_setup_cork() added by 749439bf.

We found this by debugging USGv6/ipv6ready failures. Failing
tests are: "Phase-2 Interoperability Test Scenario IPsec" /
5.3.11 and 5.4.11 (Tunnel Mode: Fragmentation).

Commit b515d2637276a3810d6595e10ab02c13bfd0b63a ("xfrm:
xfrm_state_mtu should return at least 1280 for ipv6") attempted
to fix this but caused another regression in TCP MSS calculations
and had to be reverted.

The patch below fixes the situation by dropping the MTU
check and instead checking for the underflows described in the
749439bf commit message.

Signed-off-by: Jiri Bohac <jbohac@suse.cz>
Fixes: 749439bfac6e ("ipv6: fix udpv6 sendmsg crash caused by too small MTU")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/ipv6/ip6_output.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org Feb. 25, 2022, 11:10 a.m. UTC | #1 
Hello:

This patch was applied to netdev/net.git (master)
by Steffen Klassert <steffen.klassert@secunet.com>:

On Fri, 25 Feb 2022 08:47:28 +0100 you wrote:
> From: Jiri Bohac <jbohac@suse.cz>
> 
> Commit 749439bfac6e1a2932c582e2699f91d329658196 ("ipv6: fix udpv6
> sendmsg crash caused by too small MTU") breaks PMTU for xfrm.
> 
> A Packet Too Big ICMPv6 message received in response to an ESP
> packet will prevent all further communication through the tunnel
> if the reported MTU minus the ESP overhead is smaller than 1280.
> 
> [...]

Here is the summary with links:
  - [1/6] xfrm: fix MTU regression
    https://git.kernel.org/netdev/net/c/6596a0229541

You are awesome, thank you!
diff mbox series

Patch

diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 2995f8d89e7e..4ff110214dea 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1408,8 +1408,6 @@  static int ip6_setup_cork(struct sock *sk, struct inet_cork_full *cork,
 		if (np->frag_size)
 			mtu = np->frag_size;
 	}
-	if (mtu < IPV6_MIN_MTU)
-		return -EINVAL;
 	cork->base.fragsize = mtu;
 	cork->base.gso_size = ipc6->gso_size;
 	cork->base.tx_flags = 0;
@@ -1471,8 +1469,6 @@  static int __ip6_append_data(struct sock *sk,
 
 	fragheaderlen = sizeof(struct ipv6hdr) + rt->rt6i_nfheader_len +
 			(opt ? opt->opt_nflen : 0);
-	maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen -
-		     sizeof(struct frag_hdr);
 
 	headersize = sizeof(struct ipv6hdr) +
 		     (opt ? opt->opt_flen + opt->opt_nflen : 0) +
@@ -1480,6 +1476,13 @@  static int __ip6_append_data(struct sock *sk,
 		      sizeof(struct frag_hdr) : 0) +
 		     rt->rt6i_nfheader_len;
 
+	if (mtu < fragheaderlen ||
+	    ((mtu - fragheaderlen) & ~7) + fragheaderlen < sizeof(struct frag_hdr))
+		goto emsgsize;
+
+	maxfraglen = ((mtu - fragheaderlen) & ~7) + fragheaderlen -
+		     sizeof(struct frag_hdr);
+
 	/* as per RFC 7112 section 5, the entire IPv6 Header Chain must fit
 	 * the first fragment
 	 */