From 6d381634d213580d40d431e7664dfb45f641b884 Mon Sep 17 00:00:00 2001 From: Patrick McHardy Date: Tue, 24 Oct 2006 16:15:10 -0700 Subject: [PATCH] [NETFILTER]: Fix ip6_tables extension header bypass bug As reported by Mark Dowd , ip6_tables is susceptible to a fragmentation attack causing false negatives on extension header matches. When extension headers occur in the non-first fragment after the fragment header (possibly with an incorrect nexthdr value in the fragment header) a rule looking for this extension header will never match. Drop fragments that are at offset 0 and don't contain the final protocol header regardless of the ruleset, since this should not happen normally. Since all extension headers are before the protocol header this makes sure an extension header is either not present or in the first fragment, where we can properly parse it. With help from Yasuyuki KOZAKAI . Signed-off-by: Patrick McHardy Signed-off-by: David S. Miller --- net/ipv6/netfilter/ip6_tables.c | 11 +++++++---- net/ipv6/netfilter/ip6t_ah.c | 7 ++++++- net/ipv6/netfilter/ip6t_frag.c | 7 ++++++- net/ipv6/netfilter/ip6t_hbh.c | 7 ++++++- net/ipv6/netfilter/ip6t_rt.c | 7 ++++++- 5 files changed, 31 insertions(+), 8 deletions(-) diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c index f0328c7bc1..53bf977cca 100644 --- a/net/ipv6/netfilter/ip6_tables.c +++ b/net/ipv6/netfilter/ip6_tables.c @@ -1440,6 +1440,9 @@ static void __exit ip6_tables_fini(void) * If target header is found, its offset is set in *offset and return protocol * number. Otherwise, return -1. * + * If the first fragment doesn't contain the final protocol header or + * NEXTHDR_NONE it is considered invalid. + * * Note that non-1st fragment is special case that "the protocol number * of last header" is "next header" field in Fragment header. In this case, * *offset is meaningless and fragment offset is stored in *fragoff if fragoff @@ -1463,12 +1466,12 @@ int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset, if ((!ipv6_ext_hdr(nexthdr)) || nexthdr == NEXTHDR_NONE) { if (target < 0) break; - return -1; + return -ENOENT; } hp = skb_header_pointer(skb, start, sizeof(_hdr), &_hdr); if (hp == NULL) - return -1; + return -EBADMSG; if (nexthdr == NEXTHDR_FRAGMENT) { unsigned short _frag_off, *fp; fp = skb_header_pointer(skb, @@ -1477,7 +1480,7 @@ int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset, sizeof(_frag_off), &_frag_off); if (fp == NULL) - return -1; + return -EBADMSG; _frag_off = ntohs(*fp) & ~0x7; if (_frag_off) { @@ -1488,7 +1491,7 @@ int ipv6_find_hdr(const struct sk_buff *skb, unsigned int *offset, *fragoff = _frag_off; return hp->nexthdr; } - return -1; + return -ENOENT; } hdrlen = 8; } else if (nexthdr == NEXTHDR_AUTH) diff --git a/net/ipv6/netfilter/ip6t_ah.c b/net/ipv6/netfilter/ip6t_ah.c index ec1b160815..46486645eb 100644 --- a/net/ipv6/netfilter/ip6t_ah.c +++ b/net/ipv6/netfilter/ip6t_ah.c @@ -54,9 +54,14 @@ match(const struct sk_buff *skb, const struct ip6t_ah *ahinfo = matchinfo; unsigned int ptr; unsigned int hdrlen = 0; + int err; - if (ipv6_find_hdr(skb, &ptr, NEXTHDR_AUTH, NULL) < 0) + err = ipv6_find_hdr(skb, &ptr, NEXTHDR_AUTH, NULL); + if (err < 0) { + if (err != -ENOENT) + *hotdrop = 1; return 0; + } ah = skb_header_pointer(skb, ptr, sizeof(_ah), &_ah); if (ah == NULL) { diff --git a/net/ipv6/netfilter/ip6t_frag.c b/net/ipv6/netfilter/ip6t_frag.c index 78d9c8b9e2..cd22eaaccd 100644 --- a/net/ipv6/netfilter/ip6t_frag.c +++ b/net/ipv6/netfilter/ip6t_frag.c @@ -52,9 +52,14 @@ match(const struct sk_buff *skb, struct frag_hdr _frag, *fh; const struct ip6t_frag *fraginfo = matchinfo; unsigned int ptr; + int err; - if (ipv6_find_hdr(skb, &ptr, NEXTHDR_FRAGMENT, NULL) < 0) + err = ipv6_find_hdr(skb, &ptr, NEXTHDR_FRAGMENT, NULL); + if (err < 0) { + if (err != -ENOENT) + *hotdrop = 1; return 0; + } fh = skb_header_pointer(skb, ptr, sizeof(_frag), &_frag); if (fh == NULL) { diff --git a/net/ipv6/netfilter/ip6t_hbh.c b/net/ipv6/netfilter/ip6t_hbh.c index d32a205e3a..3f25babe04 100644 --- a/net/ipv6/netfilter/ip6t_hbh.c +++ b/net/ipv6/netfilter/ip6t_hbh.c @@ -65,9 +65,14 @@ match(const struct sk_buff *skb, u8 _opttype, *tp = NULL; u8 _optlen, *lp = NULL; unsigned int optlen; + int err; - if (ipv6_find_hdr(skb, &ptr, match->data, NULL) < 0) + err = ipv6_find_hdr(skb, &ptr, match->data, NULL); + if (err < 0) { + if (err != -ENOENT) + *hotdrop = 1; return 0; + } oh = skb_header_pointer(skb, ptr, sizeof(_optsh), &_optsh); if (oh == NULL) { diff --git a/net/ipv6/netfilter/ip6t_rt.c b/net/ipv6/netfilter/ip6t_rt.c index bcb2e168a5..54d7d14134 100644 --- a/net/ipv6/netfilter/ip6t_rt.c +++ b/net/ipv6/netfilter/ip6t_rt.c @@ -58,9 +58,14 @@ match(const struct sk_buff *skb, unsigned int hdrlen = 0; unsigned int ret = 0; struct in6_addr *ap, _addr; + int err; - if (ipv6_find_hdr(skb, &ptr, NEXTHDR_ROUTING, NULL) < 0) + err = ipv6_find_hdr(skb, &ptr, NEXTHDR_ROUTING, NULL); + if (err < 0) { + if (err != -ENOENT) + *hotdrop = 1; return 0; + } rh = skb_header_pointer(skb, ptr, sizeof(_route), &_route); if (rh == NULL) { -- 2.39.5