From fc2900a908262790db3b4db7c8f4803e92b6035c Mon Sep 17 00:00:00 2001 From: Fernando Fernandez Mancera Date: Mon, 25 May 2026 17:35:54 +0200 Subject: [PATCH] netfilter: nfnetlink_osf: fix mss parsing on big-endian architectures [ Upstream commit a625c94144c9b66d32e1f374f909f38db46161c1 ] The MSS calculation in nf_osf_match_one() manually shifts bytes to construct a 16-bit value before passing it to ntohs(). This works on little-endian hosts but it does not work on big-endian as the bytes are being always shifted and set in the same way for all architectures. Use get_unaligned_be16() to fix this on big-endian systems. It also simplifies the code. Fixes: 11eeef41d5f6 ("netfilter: passive OS fingerprint xtables match") Signed-off-by: Fernando Fernandez Mancera Signed-off-by: Pablo Neira Ayuso Signed-off-by: Sasha Levin --- net/netfilter/nfnetlink_osf.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c index 6d3dfbeb398c..b61656cb0f3e 100644 --- a/net/netfilter/nfnetlink_osf.c +++ b/net/netfilter/nfnetlink_osf.c @@ -95,11 +95,7 @@ static bool nf_osf_match_one(const struct sk_buff *skb, switch (*optp) { case OSFOPT_MSS: - mss = optp[3]; - mss <<= 8; - mss |= optp[2]; - - mss = ntohs((__force __be16)mss); + mss = get_unaligned_be16(&optp[2]); break; case OSFOPT_TS: break;