From 06ff4aa252303bd2a5d706008210bb49d9889b9d Mon Sep 17 00:00:00 2001 From: Pablo Neira Ayuso Date: Fri, 13 Jul 2018 14:54:43 +0200 Subject: [PATCH] netfilter: nf_osf: add nf_osf_match_one() This new function allows us to check if there is TCP syn packet matching with a given fingerprint that can be reused from the upcoming new nf_osf_find() function. Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_osf.c | 207 ++++++++++++++++++++++++++----------------------- 1 file changed, 111 insertions(+), 96 deletions(-) diff --git a/net/netfilter/nf_osf.c b/net/netfilter/nf_osf.c index 5ba5c7b..bd7b34d 100644 --- a/net/netfilter/nf_osf.c +++ b/net/netfilter/nf_osf.c @@ -21,15 +21,14 @@ #include static inline int nf_osf_ttl(const struct sk_buff *skb, - const struct nf_osf_info *info, - unsigned char f_ttl) + int ttl_check, unsigned char f_ttl) { const struct iphdr *ip = ip_hdr(skb); - if (info->flags & NF_OSF_TTL) { - if (info->ttl == NF_OSF_TTL_TRUE) + if (ttl_check != -1) { + if (ttl_check == NF_OSF_TTL_TRUE) return ip->ttl == f_ttl; - if (info->ttl == NF_OSF_TTL_NOCHECK) + if (ttl_check == NF_OSF_TTL_NOCHECK) return 1; else if (ip->ttl <= f_ttl) return 1; @@ -52,6 +51,104 @@ static inline int nf_osf_ttl(const struct sk_buff *skb, return ip->ttl == f_ttl; } +static bool nf_osf_match_one(const struct sk_buff *skb, + const struct nf_osf_user_finger *f, + int ttl_check, u16 totlen, u16 window, + const unsigned char *optp, + unsigned int optsize) +{ + unsigned int check_WSS = 0; + int fmatch = FMATCH_WRONG; + int foptsize, optnum; + u16 mss = 0; + + if (totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl)) + return false; + + /* + * Should not happen if userspace parser was written correctly. + */ + if (f->wss.wc >= OSF_WSS_MAX) + return false; + + /* Check options */ + + foptsize = 0; + for (optnum = 0; optnum < f->opt_num; ++optnum) + foptsize += f->opt[optnum].length; + + if (foptsize > MAX_IPOPTLEN || + optsize > MAX_IPOPTLEN || + optsize != foptsize) + return false; + + check_WSS = f->wss.wc; + + for (optnum = 0; optnum < f->opt_num; ++optnum) { + if (f->opt[optnum].kind == (*optp)) { + __u32 len = f->opt[optnum].length; + const __u8 *optend = optp + len; + + fmatch = FMATCH_OK; + + switch (*optp) { + case OSFOPT_MSS: + mss = optp[3]; + mss <<= 8; + mss |= optp[2]; + + mss = ntohs((__force __be16)mss); + break; + case OSFOPT_TS: + break; + } + + optp = optend; + } else + fmatch = FMATCH_OPT_WRONG; + + if (fmatch != FMATCH_OK) + break; + } + + if (fmatch != FMATCH_OPT_WRONG) { + fmatch = FMATCH_WRONG; + + switch (check_WSS) { + case OSF_WSS_PLAIN: + if (f->wss.val == 0 || window == f->wss.val) + fmatch = FMATCH_OK; + break; + case OSF_WSS_MSS: + /* + * Some smart modems decrease mangle MSS to + * SMART_MSS_2, so we check standard, decreased + * and the one provided in the fingerprint MSS + * values. + */ +#define SMART_MSS_1 1460 +#define SMART_MSS_2 1448 + if (window == f->wss.val * mss || + window == f->wss.val * SMART_MSS_1 || + window == f->wss.val * SMART_MSS_2) + fmatch = FMATCH_OK; + break; + case OSF_WSS_MTU: + if (window == f->wss.val * (mss + 40) || + window == f->wss.val * (SMART_MSS_1 + 40) || + window == f->wss.val * (SMART_MSS_2 + 40)) + fmatch = FMATCH_OK; + break; + case OSF_WSS_MODULO: + if ((window % f->wss.val) == 0) + fmatch = FMATCH_OK; + break; + } + } + + return fmatch == FMATCH_OK; +} + bool nf_osf_match(const struct sk_buff *skb, u_int8_t family, int hooknum, struct net_device *in, struct net_device *out, @@ -59,15 +156,16 @@ nf_osf_match(const struct sk_buff *skb, u_int8_t family, const struct list_head *nf_osf_fingers) { const unsigned char *optp = NULL, *_optp = NULL; - unsigned int optsize = 0, check_WSS = 0; - int fmatch = FMATCH_WRONG, fcount = 0; const struct iphdr *ip = ip_hdr(skb); const struct nf_osf_user_finger *f; unsigned char opts[MAX_IPOPTLEN]; const struct nf_osf_finger *kf; - u16 window, totlen, mss = 0; + int fcount = 0, ttl_check; + int fmatch = FMATCH_WRONG; + unsigned int optsize = 0; const struct tcphdr *tcp; struct tcphdr _tcph; + u16 window, totlen; bool df; tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph); @@ -88,103 +186,20 @@ nf_osf_match(const struct sk_buff *skb, u_int8_t family, sizeof(struct tcphdr), optsize, opts); } + ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : -1; + list_for_each_entry_rcu(kf, &nf_osf_fingers[df], finger_entry) { - int foptsize, optnum; f = &kf->finger; if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre)) continue; - optp = _optp; - fmatch = FMATCH_WRONG; - - if (totlen != f->ss || !nf_osf_ttl(skb, info, f->ttl)) - continue; - - /* - * Should not happen if userspace parser was written correctly. - */ - if (f->wss.wc >= OSF_WSS_MAX) + if (!nf_osf_match_one(skb, f, + ttl_check, totlen, window, optp, optsize)) continue; - /* Check options */ - - foptsize = 0; - for (optnum = 0; optnum < f->opt_num; ++optnum) - foptsize += f->opt[optnum].length; - - if (foptsize > MAX_IPOPTLEN || - optsize > MAX_IPOPTLEN || - optsize != foptsize) - continue; - - check_WSS = f->wss.wc; - - for (optnum = 0; optnum < f->opt_num; ++optnum) { - if (f->opt[optnum].kind == (*optp)) { - __u32 len = f->opt[optnum].length; - const __u8 *optend = optp + len; - - fmatch = FMATCH_OK; - - switch (*optp) { - case OSFOPT_MSS: - mss = optp[3]; - mss <<= 8; - mss |= optp[2]; - - mss = ntohs((__force __be16)mss); - break; - case OSFOPT_TS: - break; - } - - optp = optend; - } else - fmatch = FMATCH_OPT_WRONG; - - if (fmatch != FMATCH_OK) - break; - } - - if (fmatch != FMATCH_OPT_WRONG) { - fmatch = FMATCH_WRONG; - - switch (check_WSS) { - case OSF_WSS_PLAIN: - if (f->wss.val == 0 || window == f->wss.val) - fmatch = FMATCH_OK; - break; - case OSF_WSS_MSS: - /* - * Some smart modems decrease mangle MSS to - * SMART_MSS_2, so we check standard, decreased - * and the one provided in the fingerprint MSS - * values. - */ -#define SMART_MSS_1 1460 -#define SMART_MSS_2 1448 - if (window == f->wss.val * mss || - window == f->wss.val * SMART_MSS_1 || - window == f->wss.val * SMART_MSS_2) - fmatch = FMATCH_OK; - break; - case OSF_WSS_MTU: - if (window == f->wss.val * (mss + 40) || - window == f->wss.val * (SMART_MSS_1 + 40) || - window == f->wss.val * (SMART_MSS_2 + 40)) - fmatch = FMATCH_OK; - break; - case OSF_WSS_MODULO: - if ((window % f->wss.val) == 0) - fmatch = FMATCH_OK; - break; - } - } - - if (fmatch != FMATCH_OK) - continue; + fmatch = FMATCH_OK; fcount++; -- 2.7.4