[PATCH 2/2] ubi: build: replace simple_strtoul with kstrtoul in bytes_str_to_int()

["haoyu.lu" <hechushiguitu666@gmail.com>]

From: Haoyu Lu <hechushiguitu666@gmail.com>

Replace the deprecated simple_strtoul() with kstrtoul() in the
bytes_str_to_int() helper function. Since kstrtoul() rejects trailing
non-numeric characters (such as the G/M/K suffixes), the numeric prefix
is first extracted with strspn() and then parsed separately before
handling the suffix.

This provides proper error handling through the kstrto* family while
preserving the existing suffix semantics for byte count parameters.

Note: the original simple_strtoul() with base=0 accepted hexadecimal
(0x prefix) and octal (0 prefix) formats, while kstrtoul() with base=10
only supports decimal. This is not a practical concern since MTD byte
count parameters are always specified as decimal values in boot
parameters.

Signed-off-by: Haoyu Lu <hechushiguitu666@gmail.com>
---
 drivers/mtd/ubi/build.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 03ef195dc25c..7cb6ba4a3840 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -1426,16 +1426,27 @@ module_exit(ubi_exit);
  */
 static int bytes_str_to_int(const char *str)
 {
-	char *endp;
 	unsigned long result;
+	unsigned int num_len;
+	char num_buf[32];
 
-	result = simple_strtoul(str, &endp, 0);
-	if (str == endp || result >= INT_MAX) {
+	/* Find the length of the numeric prefix */
+	num_len = strspn(str, "0123456789");
+	if (num_len == 0 || num_len >= sizeof(num_buf)) {
 		pr_err("UBI error: incorrect bytes count: \"%s\"\n", str);
 		return -EINVAL;
 	}
 
-	switch (*endp) {
+	/* Parse the numeric part */
+	memcpy(num_buf, str, num_len);
+	num_buf[num_len] = '\0';
+	if (kstrtoul(num_buf, 10, &result) < 0 || result >= INT_MAX) {
+		pr_err("UBI error: incorrect bytes count: \"%s\"\n", str);
+		return -EINVAL;
+	}
+
+	/* Handle suffix */
+	switch (str[num_len]) {
 	case 'G':
 		result *= 1024;
 		fallthrough;
-- 
2.17.1