[Devel] [PATCH RHEL7 COMMIT] ms/ipv4: ip_do_fragment: fix headroom tests

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.26.1.vz7.33.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.26.1.vz7.33.8
------>
commit fdcf72515c5b548142d8913b3003447a4cbbefe2
Author: Vasily Averin <vvs at virtuozzo.com>
Date:   Mon Jul 17 18:56:14 2017 +0400

    ms/ipv4: ip_do_fragment: fix headroom tests
    
    Some time ago David Woodhouse reported skb_under_panic
    when we try to push ethernet header to fragmented ipv6 skbs.
    It was fixed for ipv6 by Florian Westphal in
    commit 1d325d217c7f ("ipv6: ip6_fragment: fix headroom tests and skb leak")
    
    However similar problem still exist in ipv4.
    
    It does not trigger skb_under_panic due paranoid check
    in ip_finish_output2, however according to Alexey Kuznetsov
    current state is abnormal and ip_fragment should be fixed too.
    
    https://jira.sw.ru/browse/PSBM-68362
    
    Applied to netdev@ repo:
    https://patchwork.ozlabs.org/patch/788222/
    
    Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 net/ipv4/ip_output.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 85274fa..84cbbe7 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -560,6 +560,7 @@ int ip_do_fragment(struct sock *sk, struct sk_buff *skb,
 	hlen = iph->ihl * 4;
 	mtu = mtu - hlen;	/* Size of data space */
 	IPCB(skb)->flags |= IPSKB_FRAG_COMPLETE;
+	ll_rs = LL_RESERVED_SPACE(rt->dst.dev);
 
 	/* When frag_list is given, use it. First, check its validity:
 	 * some transformers could create wrong frag_list or break existing
@@ -575,14 +576,15 @@ int ip_do_fragment(struct sock *sk, struct sk_buff *skb,
 		if (first_len - hlen > mtu ||
 		    ((first_len - hlen) & 7) ||
 		    ip_is_fragment(iph) ||
-		    skb_cloned(skb))
+		    skb_cloned(skb) ||
+		    skb_headroom(skb) < ll_rs)
 			goto slow_path;
 
 		skb_walk_frags(skb, frag) {
 			/* Correct geometry. */
 			if (frag->len > mtu ||
 			    ((frag->len & 7) && frag->next) ||
-			    skb_headroom(frag) < hlen)
+			    skb_headroom(frag) < hlen + ll_rs)
 				goto slow_path_clean;
 
 			/* Partially cloned skb? */
@@ -672,8 +674,6 @@ int ip_do_fragment(struct sock *sk, struct sk_buff *skb,
 	left = skb->len - hlen;		/* Space per frame */
 	ptr = hlen;		/* Where to start from */
 
-	ll_rs = LL_RESERVED_SPACE(rt->dst.dev);
-
 	/*
 	 *	Fragment the datagram.
 	 */