Subject: Re: More IPSEC trouble

From: Patrick McHardy <[email-masked]>
Date: Sat, 12 Mar 2005 01:11:37 +0100

Patrick McHardy wrote:
> Steve Hill wrote:
> 
>> This was a configuration mistake on my part and admittedly it 
>> shouldn't work properly - however, it triggered a kernel bug: sending 
>> a packet with the DF flag set which will grow to be > the MTU when 
>> encrypted causes the kernel to generate an ICMP Frag Needed packet, 
>> which got caught by the policy and this triggered the kernel to lock 
>> up hard.
> 
> 
> Thanks for tracking this down, we need to unlock the state before
> calling icmp_send(). This patch fixes it, it should apply to 2.6.10
> if you replace dst_mtu() by dst_pmtu() in the context.

Second try .. this one compiles.

# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
#   2005/03/12 00:59:07+01:00 [email-masked] 
#   [XFRM]: Avoid possible deadlock for locally generated ICMP errors
#   
#   Signed-off-by: Patrick McHardy <[email-masked]>
# 
# net/ipv6/xfrm6_output.c
#   2005/03/12 00:58:59+01:00 [email-masked] +3 -1
#   [XFRM]: Avoid possible deadlock for locally generated ICMP errors
#   
#   Signed-off-by: Patrick McHardy <[email-masked]>
# 
# net/ipv4/xfrm4_output.c
#   2005/03/12 00:58:59+01:00 [email-masked] +3 -1
#   [XFRM]: Avoid possible deadlock for locally generated ICMP errors
#   
#   Signed-off-by: Patrick McHardy <[email-masked]>
# 
diff -Nru a/net/ipv4/xfrm4_output.c b/net/ipv4/xfrm4_output.c
--- a/net/ipv4/xfrm4_output.c	2005-03-12 01:03:18 +01:00
+++ b/net/ipv4/xfrm4_output.c	2005-03-12 01:03:18 +01:00
@@ -84,6 +84,7 @@
 	dst = skb->dst;
 	mtu = dst_mtu(dst);
 	if (skb->len > mtu) {
+		spin_unlock_bh(&x->lock);
 		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
 		ret = -EMSGSIZE;
 	}
@@ -111,7 +112,8 @@
 	if (x->props.mode) {
 		err = xfrm4_tunnel_check_size(skb);
 		if (err)
-			goto error;
+			/* xfrm4_tunnel_check_size() drops the lock on error */
+			goto error_nolock;
 	}
 
 	xfrm4_encap(skb);
diff -Nru a/net/ipv6/xfrm6_output.c b/net/ipv6/xfrm6_output.c
--- a/net/ipv6/xfrm6_output.c	2005-03-12 01:03:18 +01:00
+++ b/net/ipv6/xfrm6_output.c	2005-03-12 01:03:18 +01:00
@@ -84,6 +84,7 @@
 		mtu = IPV6_MIN_MTU;
 
 	if (skb->len > mtu) {
+		spin_unlock_bh(&x->lock);
 		icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu, skb->dev);
 		ret = -EMSGSIZE;
 	}
@@ -111,7 +112,8 @@
 	if (x->props.mode) {
 		err = xfrm6_tunnel_check_size(skb);
 		if (err)
-			goto error;
+			/* xfrm6_tunnel_check_size drops the lock on error */
+			goto error_nolock;
 	}
 
 	xfrm6_encap(skb);