From: Fernando Fernandez Mancera Date: Fri, 17 Apr 2026 16:20:56 +0000 (+0200) Subject: netfilter: nfnetlink_osf: fix out-of-bounds read on option matching X-Git-Tag: v7.1-rc1~36^2~23^2~1 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f5ca450087c3baf3651055e7a6de92600f827af3;p=thirdparty%2Fkernel%2Flinux.git netfilter: nfnetlink_osf: fix out-of-bounds read on option matching In nf_osf_match(), the nf_osf_hdr_ctx structure is initialized once and passed by reference to nf_osf_match_one() for each fingerprint checked. During TCP option parsing, nf_osf_match_one() advances the shared ctx->optp pointer. If a fingerprint perfectly matches, the function returns early without restoring ctx->optp to its initial state. If the user has configured NF_OSF_LOGLEVEL_ALL, the loop continues to the next fingerprint. However, because ctx->optp was not restored, the next call to nf_osf_match_one() starts parsing from the end of the options buffer. This causes subsequent matches to read garbage data and fail immediately, making it impossible to log more than one match or logging incorrect matches. Instead of using a shared ctx->optp pointer, pass the context as a constant pointer and use a local pointer (optp) for TCP option traversal. This makes nf_osf_match_one() strictly stateless from the caller's perspective, ensuring every fingerprint check starts at the correct option offset. Fixes: 1a6a0951fc00 ("netfilter: nfnetlink_osf: add missing fmatch check") Suggested-by: Florian Westphal Signed-off-by: Fernando Fernandez Mancera Reviewed-by: Pablo Neira Ayuso Signed-off-by: Pablo Neira Ayuso --- diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c index 9de91fdd107c..9b209241029b 100644 --- a/net/netfilter/nfnetlink_osf.c +++ b/net/netfilter/nfnetlink_osf.c @@ -64,9 +64,9 @@ struct nf_osf_hdr_ctx { static bool nf_osf_match_one(const struct sk_buff *skb, const struct nf_osf_user_finger *f, int ttl_check, - struct nf_osf_hdr_ctx *ctx) + const struct nf_osf_hdr_ctx *ctx) { - const __u8 *optpinit = ctx->optp; + const __u8 *optp = ctx->optp; unsigned int check_WSS = 0; int fmatch = FMATCH_WRONG; int foptsize, optnum; @@ -95,17 +95,17 @@ static bool nf_osf_match_one(const struct sk_buff *skb, check_WSS = f->wss.wc; for (optnum = 0; optnum < f->opt_num; ++optnum) { - if (f->opt[optnum].kind == *ctx->optp) { + if (f->opt[optnum].kind == *optp) { __u32 len = f->opt[optnum].length; - const __u8 *optend = ctx->optp + len; + const __u8 *optend = optp + len; fmatch = FMATCH_OK; - switch (*ctx->optp) { + switch (*optp) { case OSFOPT_MSS: - mss = ctx->optp[3]; + mss = optp[3]; mss <<= 8; - mss |= ctx->optp[2]; + mss |= optp[2]; mss = ntohs((__force __be16)mss); break; @@ -113,7 +113,7 @@ static bool nf_osf_match_one(const struct sk_buff *skb, break; } - ctx->optp = optend; + optp = optend; } else fmatch = FMATCH_OPT_WRONG; @@ -156,9 +156,6 @@ static bool nf_osf_match_one(const struct sk_buff *skb, } } - if (fmatch != FMATCH_OK) - ctx->optp = optpinit; - return fmatch == FMATCH_OK; }