netdev - [PATCH iproute2] libnetlink: validate nlmsg header length first

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Message-ID: <20231107012147.668074-1-maxdev@posteo.de>
Date: Tue,  7 Nov 2023 01:20:55 +0000
From: Max Kunzelmann <maxdev@...teo.de>
To: netdev@...r.kernel.org
Cc: stephen@...workplumber.org,
	dsahern@...il.com,
	Max Kunzelmann <maxdev@...teo.de>,
	Benny Baumann <BenBE@...hi.org>,
	Robert Geislinger <github@...ykng.de>
Subject: [PATCH iproute2] libnetlink: validate nlmsg header length first

Validate the nlmsg header length before accessing the nlmsg payload
length.

Fixes: 892a25e286fb ("libnetlink: break up dump function")

Signed-off-by: Max Kunzelmann <maxdev@...teo.de>
Reviewed-by: Benny Baumann <BenBE@...hi.org>
Reviewed-by: Robert Geislinger <github@...ykng.de>
---
 lib/libnetlink.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 7edcd285..01648229 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -727,13 +727,15 @@ int rtnl_dump_request_n(struct rtnl_handle *rth, struct nlmsghdr *n)
 static int rtnl_dump_done(struct nlmsghdr *h,
 			  const struct rtnl_dump_filter_arg *a)
 {
-	int len = *(int *)NLMSG_DATA(h);
+	int len;
 
 	if (h->nlmsg_len < NLMSG_LENGTH(sizeof(int))) {
 		fprintf(stderr, "DONE truncated\n");
 		return -1;
 	}
 
+	len = *(int *)NLMSG_DATA(h);
+
 	if (len < 0) {
 		errno = -len;
 
-- 
2.42.0