[PATCH net 9/9] netfilter: xt_connmark: reject invalid shift parameters

[Florian Westphal <fw@strlen.de>]

From: Wyatt Feng <bronzed_45_vested@icloud.com>

Revision 2 of the CONNMARK target accepts user-controlled shift
parameters and applies them to 32-bit mark values in
connmark_tg_shift().

A shift_bits value of 32 or more triggers an undefined-shift bug when
the rule is evaluated. Invalid shift_dir values are also accepted and
silently fall back to the left-shift path.

Reject invalid revision-2 shift parameters in connmark_tg_check() so
malformed rules fail at installation time, before they can reach the
packet path.

Fixes: 472a73e00757 ("netfilter: xt_conntrack: Support bit-shifting for CONNMARK & MARK targets.")
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Zhengchuan Liang <zcliangcn@gmail.com>
Reported-by: Xin Liu <dstsmallbird@foxmail.com>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Wyatt Feng <bronzed_45_vested@icloud.com>
Reviewed-by: Ren Wei <enjou1224z@gmail.com>
Reviewed-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/xt_connmark.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/xt_connmark.c b/net/netfilter/xt_connmark.c
index 4277084de2e7..2cf27f7d59b9 100644
--- a/net/netfilter/xt_connmark.c
+++ b/net/netfilter/xt_connmark.c
@@ -112,6 +112,16 @@ static int connmark_tg_check(const struct xt_tgchk_param *par)
 	return ret;
 }
 
+static int connmark_tg_check_v2(const struct xt_tgchk_param *par)
+{
+	const struct xt_connmark_tginfo2 *info = par->targinfo;
+
+	if (info->shift_dir > D_SHIFT_RIGHT || info->shift_bits >= 32)
+		return -EINVAL;
+
+	return connmark_tg_check(par);
+}
+
 static void connmark_tg_destroy(const struct xt_tgdtor_param *par)
 {
 	nf_ct_netns_put(par->net, par->family);
@@ -162,7 +172,7 @@ static struct xt_target connmark_tg_reg[] __read_mostly = {
 		.name           = "CONNMARK",
 		.revision       = 2,
 		.family         = NFPROTO_IPV4,
-		.checkentry     = connmark_tg_check,
+		.checkentry     = connmark_tg_check_v2,
 		.target         = connmark_tg_v2,
 		.targetsize     = sizeof(struct xt_connmark_tginfo2),
 		.destroy        = connmark_tg_destroy,
@@ -183,7 +193,7 @@ static struct xt_target connmark_tg_reg[] __read_mostly = {
 		.name           = "CONNMARK",
 		.revision       = 2,
 		.family         = NFPROTO_IPV6,
-		.checkentry     = connmark_tg_check,
+		.checkentry     = connmark_tg_check_v2,
 		.target         = connmark_tg_v2,
 		.targetsize     = sizeof(struct xt_connmark_tginfo2),
 		.destroy        = connmark_tg_destroy,
-- 
2.54.0