kernel: ipv6: ip6_fragment: fix headroom tests and skb leak

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 46992

1 files changed, 101 insertions, 0 deletions

diff --git a/target/linux/generic/patches-3.18/082-ipv6-ip6_fragment-fix-headroom-tests-and-skb-leak.patch b/target/linux/generic/patches-3.18/082-ipv6-ip6_fragment-fix-headroom-tests-and-skb-leak.patch
new file mode 100644
index 0000000000..7c833c4102
--- /dev/null
+++ b/target/linux/generic/patches-3.18/082-ipv6-ip6_fragment-fix-headroom-tests-and-skb-leak.patch
@@ -0,0 +1,101 @@
+From: Florian Westphal <fw@strlen.de>
+Date: Thu, 17 Sep 2015 11:24:48 +0100
+Subject: [PATCH] ipv6: ip6_fragment: fix headroom tests and skb leak
+
+David Woodhouse reports skb_under_panic when we try to push ethernet
+header to fragmented ipv6 skbs:
+
+ skbuff: skb_under_panic: text:c1277f1e len:1294 put:14 head:dec98000
+ data:dec97ffc tail:0xdec9850a end:0xdec98f40 dev:br-lan
+[..]
+ip6_finish_output2+0x196/0x4da
+
+David further debugged this:
+  [..] offending fragments were arriving here with skb_headroom(skb)==10.
+  Which is reasonable, being the Solos ADSL card's header of 8 bytes
+  followed by 2 bytes of PPP frame type.
+
+The problem is that if netfilter ipv6 defragmentation is used, skb_cow()
+in ip6_forward will only see reassembled skb.
+
+Therefore, headroom is overestimated by 8 bytes (we pulled fragment
+header) and we don't check the skbs in the frag_list either.
+
+We can't do these checks in netfilter defrag since outdev isn't known yet.
+
+Furthermore, existing tests in ip6_fragment did not consider the fragment
+or ipv6 header size when checking headroom of the fraglist skbs.
+
+While at it, also fix a skb leak on memory allocation -- ip6_fragment
+must consume the skb.
+
+I tested this e1000 driver hacked to not allocate additional headroom
+(we end up in slowpath, since LL_RESERVED_SPACE is 16).
+
+If 2 bytes of headroom are allocated, fastpath is taken (14 byte
+ethernet header was pulled, so 16 byte headroom available in all
+fragments).
+
+Reported-by: David Woodhouse <dwmw2@infradead.org>
+Diagnosed-by: David Woodhouse <dwmw2@infradead.org>
+Signed-off-by: Florian Westphal <fw@strlen.de>
+Closes 20532
+---
+
+--- a/net/ipv6/ip6_output.c
++++ b/net/ipv6/ip6_output.c
+@@ -594,20 +594,22 @@ int ip6_fragment(struct sk_buff *skb, in
+ 	}
+ 	mtu -= hlen + sizeof(struct frag_hdr);
+ 
++	hroom = LL_RESERVED_SPACE(rt->dst.dev);
+ 	if (skb_has_frag_list(skb)) {
+ 		int first_len = skb_pagelen(skb);
+ 		struct sk_buff *frag2;
+ 
+ 		if (first_len - hlen > mtu ||
+ 		    ((first_len - hlen) & 7) ||
+-		    skb_cloned(skb))
++		    skb_cloned(skb) ||
++		    skb_headroom(skb) < (hroom + sizeof(struct frag_hdr)))
+ 			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 + hroom + sizeof(struct frag_hdr)))
+ 				goto slow_path_clean;
+ 
+ 			/* Partially cloned skb? */
+@@ -624,8 +626,6 @@ int ip6_fragment(struct sk_buff *skb, in
+ 
+ 		err = 0;
+ 		offset = 0;
+-		frag = skb_shinfo(skb)->frag_list;
+-		skb_frag_list_init(skb);
+ 		/* BUILD HEADER */
+ 
+ 		*prevhdr = NEXTHDR_FRAGMENT;
+@@ -633,8 +633,11 @@ int ip6_fragment(struct sk_buff *skb, in
+ 		if (!tmp_hdr) {
+ 			IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
+ 				      IPSTATS_MIB_FRAGFAILS);
+-			return -ENOMEM;
++			err = -ENOMEM;
++			goto fail;
+ 		}
++		frag = skb_shinfo(skb)->frag_list;
++		skb_frag_list_init(skb);
+ 
+ 		__skb_pull(skb, hlen);
+ 		fh = (struct frag_hdr *)__skb_push(skb, sizeof(struct frag_hdr));
+@@ -732,7 +735,6 @@ slow_path:
+ 	 */
+ 
+ 	*prevhdr = NEXTHDR_FRAGMENT;
+-	hroom = LL_RESERVED_SPACE(rt->dst.dev);
+ 	troom = rt->dst.dev->needed_tailroom;
+ 
+ 	/*