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

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Message-ID: <20260108165216.1054625-1-dmantipov@yandex.ru>
Date: Thu,  8 Jan 2026 19:52:15 +0300
From: Dmitry Antipov <dmantipov@...dex.ru>
To: Carlos Maiolino <cem@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Kees Cook <kees@...nel.org>,
	Andy Shevchenko <andy@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-xfs@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Dmitry Antipov <dmantipov@...dex.ru>
Subject: [PATCH v3 1/2] lib: introduce simple error-checking wrapper for memparse()

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@...radead.org>
Suggested-by: Kees Cook <kees@...nel.org>
Signed-off-by: Dmitry Antipov <dmantipov@...dex.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