[PATCH v3 1/2] lib: introduce simple error-checking wrapper for memparse()

Dmitry Antipov
2026-01-08T16:53:37Z

Introduce 'memvalue()' which uses 'memparse()' to parse a string
with optional memory suffix into a non-negative number. If parsing
has succeeded, returns 0 and stores the result at the location
specified by the second argument. Otherwise returns -EINVAL and
leaves the location untouched.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Kees Cook <kees@kernel.org>
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
---
v3: adjust as suggested by Kees and bump version to match the series
---
include/linux/string.h | 1 +
lib/cmdline.c | 26 ++++++++++++++++++++++++++
2 files changed, 27 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index 1b564c36d721..470c7051c58b 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -319,6 +319,7 @@ DEFINE_FREE(argv_free, char **, if (!IS_ERR_OR_NULL(_T)) argv_free(_T))
extern int get_option(char **str, int *pint);
extern char *get_options(const char *str, int nints, int *ints);
extern unsigned long long memparse(const char *ptr, char **retptr);
+extern int __must_check memvalue(const char *ptr, unsigned long long *valptr);
extern bool parse_option_str(const char *str, const char *option);
extern char *next_arg(char *args, char **param, char **val);

diff --git a/lib/cmdline.c b/lib/cmdline.c
index 90ed997d9570..cf81c6363f6c 100644
--- a/lib/cmdline.c
+++ b/lib/cmdline.c
@@ -190,6 +190,32 @@ unsigned long long memparse(const char *ptr, char **retptr)
}
EXPORT_SYMBOL(memparse);

+/**
+ * memvalue - Wrap memparse() with simple error detection
+ * @ptr: Where parse begins
+ * @valptr: Where to store result
+ *
+ * Unconditionally returns -EINVAL for a presumably negative value.
+ * Otherwise uses memparse() to parse a string into a number stored
+ * at @valptr and returns 0 or -EINVAL if an unrecognized character
+ * was encountered. For a non-zero return value, memory at @valptr
+ * is left untouched.
+ */
+int __must_check memvalue(const char *ptr, unsigned long long *valptr)
+{
+ unsigned long long ret;
+ char *end;
+
+ if (*ptr == '-')
+ return -EINVAL;
+ ret = memparse(ptr, &end);
+ if (*end)
+ return -EINVAL;
+ *valptr = ret;
+ return 0;
+}
+EXPORT_SYMBOL(memvalue);
+
/**
* parse_option_str - Parse a string and check an option is set or not
* @str: String to be parsed
--
2.52.0