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- 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
- @@ -597,20 +597,22 @@ 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? */
- @@ -627,8 +629,6 @@ 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;
- @@ -636,8 +636,11 @@ 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));
- @@ -735,7 +738,6 @@ slow_path:
- */
-
- *prevhdr = NEXTHDR_FRAGMENT;
- - hroom = LL_RESERVED_SPACE(rt->dst.dev);
- troom = rt->dst.dev->needed_tailroom;
-
- /*
|
