[PATCH-next v4] lib: parser: optimize match_NUMBER apis to use local array

[Li Lingfeng <lilingfeng3@xxxxxxxxxx>]

Memory will be allocated to store substring_t in match_strdup(), which
means the caller of match_strdup() may need to be scheduled out to wait
for reclaiming memory.

Using local array to store substring_t to remove the restriction.

Link: https://lore.kernel.org/all/20221104023938.2346986-5-yukuai1@xxxxxxxxxxxxxxx/
Signed-off-by: Li Lingfeng <lilingfeng3@xxxxxxxxxx>
---
 v1->v2:
   change the name of buffer's length
   use match_strlcpy() to copy string and keep string length check
 v2->v3:
   judge whether the length to be copied exceeds the limit by the 
   return value of match_strlcpy()
 v3->v4:
   fix typos in title
   format the commit message
   complete the modification which should be done in v3
 lib/parser.c | 39 ++++++++++++++++++++-------------------
 1 file changed, 20 insertions(+), 19 deletions(-)

diff --git a/lib/parser.c b/lib/parser.c
index bcb23484100e..2b5e2b480253 100644
--- a/lib/parser.c
+++ b/lib/parser.c
@@ -11,6 +11,15 @@
 #include <linux/slab.h>
 #include <linux/string.h>
 
+/*
+ * max size needed by different bases to express U64
+ * HEX: "0xFFFFFFFFFFFFFFFF" --> 18
+ * DEC: "18446744073709551615" --> 20
+ * OCT: "01777777777777777777777" --> 23
+ * pick the max one to define NUMBER_BUF_LEN
+ */
+#define NUMBER_BUF_LEN 24
+
 /**
  * match_one - Determines if a string matches a simple pattern
  * @s: the string to examine for presence of the pattern
@@ -129,14 +138,12 @@ EXPORT_SYMBOL(match_token);
 static int match_number(substring_t *s, int *result, int base)
 {
 	char *endp;
-	char *buf;
+	char buf[NUMBER_BUF_LEN];
 	int ret;
 	long val;
 
-	buf = match_strdup(s);
-	if (!buf)
-		return -ENOMEM;
-
+	if (match_strlcpy(buf, s, NUMBER_BUF_LEN) >= NUMBER_BUF_LEN)
+		return -ERANGE;
 	ret = 0;
 	val = simple_strtol(buf, &endp, base);
 	if (endp == buf)
@@ -145,7 +152,6 @@ static int match_number(substring_t *s, int *result, int base)
 		ret = -ERANGE;
 	else
 		*result = (int) val;
-	kfree(buf);
 	return ret;
 }
 
@@ -163,18 +169,15 @@ static int match_number(substring_t *s, int *result, int base)
  */
 static int match_u64int(substring_t *s, u64 *result, int base)
 {
-	char *buf;
+	char buf[NUMBER_BUF_LEN];
 	int ret;
 	u64 val;
 
-	buf = match_strdup(s);
-	if (!buf)
-		return -ENOMEM;
-
+	if (match_strlcpy(buf, s, NUMBER_BUF_LEN) >= NUMBER_BUF_LEN)
+		return -ERANGE;
 	ret = kstrtoull(buf, base, &val);
 	if (!ret)
 		*result = val;
-	kfree(buf);
 	return ret;
 }
 
@@ -206,14 +209,12 @@ EXPORT_SYMBOL(match_int);
  */
 int match_uint(substring_t *s, unsigned int *result)
 {
-	int err = -ENOMEM;
-	char *buf = match_strdup(s);
+	char buf[NUMBER_BUF_LEN];
 
-	if (buf) {
-		err = kstrtouint(buf, 10, result);
-		kfree(buf);
-	}
-	return err;
+	if (match_strlcpy(buf, s, NUMBER_BUF_LEN) >= NUMBER_BUF_LEN)
+		return -ERANGE;
+
+	return kstrtouint(buf, 10, result);
 }
 EXPORT_SYMBOL(match_uint);
 
-- 
2.31.1