From: Florian Westphal 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 Diagnosed-by: David Woodhouse Signed-off-by: Florian Westphal Closes 20532 --- --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -602,20 +602,22 @@ 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? */ @@ -632,8 +634,6 @@ 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; @@ -641,8 +641,11 @@ 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)); @@ -740,7 +743,6 @@ slow_path: */ *prevhdr = NEXTHDR_FRAGMENT; - hroom = LL_RESERVED_SPACE(rt->dst.dev); troom = rt->dst.dev->needed_tailroom; /*