From: Jiri Bohac jbohac@suse.cz
commit 6596a0229541270fb8d38d989f91b78838e5e9da upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv6/ip6_output.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
--- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -1432,8 +1432,6 @@ static int ip6_setup_cork(struct sock *s 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; @@ -1495,8 +1493,6 @@ static int __ip6_append_data(struct sock
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) + @@ -1504,6 +1500,13 @@ static int __ip6_append_data(struct sock 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 */