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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
@@ -584,20 +584,22 @@ int ip6_fragment(struct sock *sk, struct
}
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? */
@@ -614,8 +616,6 @@ int ip6_fragment(struct sock *sk, struct
err = 0;
offset = 0;
- frag = skb_shinfo(skb)->frag_list;
- skb_frag_list_init(skb);
/* BUILD HEADER */
*prevhdr = NEXTHDR_FRAGMENT;
@@ -623,8 +623,11 @@ int ip6_fragment(struct sock *sk, struct
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));
@@ -722,7 +725,6 @@ slow_path:
*/
*prevhdr = NEXTHDR_FRAGMENT;
- hroom = LL_RESERVED_SPACE(rt->dst.dev);
troom = rt->dst.dev->needed_tailroom;
/*
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