netdev - [PATCH net-next] netfilter: nfnetlink_hook: fix check for snprintf() overflow

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Date:   Sat, 19 Jun 2021 16:55:46 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH net-next] netfilter: nfnetlink_hook: fix check for snprintf()
 overflow

The kernel version of snprintf() can't return negatives.  The
"ret > (int)sizeof(sym)" check is off by one because and it should be
>=.  Finally, we need to set a negative error code.

Fixes: e2cf17d3774c ("netfilter: add new hook nfnl subsystem")
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---
 net/netfilter/nfnetlink_hook.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nfnetlink_hook.c b/net/netfilter/nfnetlink_hook.c
index 58fda6ac663b..50b4e3c9347a 100644
--- a/net/netfilter/nfnetlink_hook.c
+++ b/net/netfilter/nfnetlink_hook.c
@@ -126,8 +126,10 @@ static int nfnl_hook_dump_one(struct sk_buff *nlskb,
 
 #ifdef CONFIG_KALLSYMS
 	ret = snprintf(sym, sizeof(sym), "%ps", ops->hook);
-	if (ret < 0 || ret > (int)sizeof(sym))
+	if (ret >= sizeof(sym)) {
+		ret = -EINVAL;
 		goto nla_put_failure;
+	}
 
 	module_name = strstr(sym, " [");
 	if (module_name) {
-- 
2.30.2