netdev - [PATCH ethtool v2 13/13] ethtool: fix bug and use standard string parsing

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Date:   Wed,  7 Dec 2022 17:11:22 -0800
From:   Jesse Brandeburg <jesse.brandeburg@...el.com>
To:     mkubecek@...e.cz
Cc:     netdev@...r.kernel.org,
        Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: [PATCH ethtool v2 13/13] ethtool: fix bug and use standard string parsing

The parse_reset function was open-coding string parsing routines and can
be converted to using standard routines. It was trying to be tricky and
parse partial strings to make things like "mgmt" and "mgmt-shared"
strings mostly use the same code. This is better done with strncmp().

This also fixes an array overflow bug where it's possible for the for
loop to access past the end of the input array, which is bad.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
---
 ethtool.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/ethtool.c b/ethtool.c
index 4776afe89e23..d294b5f8d92a 100644
--- a/ethtool.c
+++ b/ethtool.c
@@ -5280,17 +5280,21 @@ static int do_get_phy_tunable(struct cmd_context *ctx)
 static __u32 parse_reset(char *val, __u32 bitset, char *arg, __u32 *data)
 {
 	__u32 bitval = 0;
-	int i;
+	int vallen = strlen(val);
+	int strret;
 
 	/* Check for component match */
-	for (i = 0; val[i] != '\0'; i++)
-		if (arg[i] != val[i])
-			return 0;
+	strret = strncmp(arg, val, vallen);
+	if (strret < 0)
+		return 0;
 
-	/* Check if component has -shared specified or not */
-	if (arg[i] == '\0')
+	/* if perfect match to val
+	 * else
+	 * Check if component has -shared specified or not
+	 */
+	if (strret == 0)
 		bitval = bitset;
-	else if (!strcmp(arg+i, "-shared"))
+	else if (!strcmp(arg + vallen, "-shared"))
 		bitval = bitset << ETH_RESET_SHARED_SHIFT;
 
 	if (bitval) {
-- 
2.31.1