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netfilter: nfnetlink_osf: fix mss parsing on big-endian architectures

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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: 11eeef41d5 ("netfilter: passive OS fingerprint xtables match")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Fernando Fernandez Mancera 2026-05-25 17:35:54 +02:00 committed by Pablo Neira Ayuso
parent 4a15044a2b
commit a625c94144
1 changed files with 1 additions and 5 deletions
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6
net/netfilter/nfnetlink_osf.c
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@ -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;