linux-hardening - [PATCH v4 3/5] string: add strends() helper to check if a string ends with a suffix

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Message-ID: <20240930113045.28616-4-ansuelsmth@gmail.com>
Date: Mon, 30 Sep 2024 13:30:10 +0200
From: Christian Marangi <ansuelsmth@...il.com>
To: Jens Axboe <axboe@...nel.dk>,
	Jonathan Corbet <corbet@....net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Kees Cook <kees@...nel.org>,
	Andy Shevchenko <andy@...nel.org>,
	Christian Marangi <ansuelsmth@...il.com>,
	Daniel Golle <daniel@...rotopia.org>,
	INAGAKI Hiroshi <musashino.open@...il.com>,
	Christian Brauner <brauner@...nel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Li Lingfeng <lilingfeng3@...wei.com>,
	Ming Lei <ming.lei@...hat.com>,
	Christian Heusel <christian@...sel.eu>,
	linux-block@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-mmc@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Miquel Raynal <miquel.raynal@...tlin.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	upstream@...oha.com
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: [PATCH v4 3/5] string: add strends() helper to check if a string ends with a suffix

Add strends() helper to check if a string ends with a suffix. The
unreadable strends is chosen to keep consistency with the parallel
strstarts helper used to check if a string starts with a prefix.

To prevent out-of-bounds read, len of string is checked against the
prefix length before comparing the 2 string at the offset.

Suggested-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
---
 include/linux/string.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/string.h b/include/linux/string.h
index 0dd27afcfaf7..2c3df6ffb326 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -353,6 +353,19 @@ static inline bool strstarts(const char *str, const char *prefix)
 	return strncmp(str, prefix, strlen(prefix)) == 0;
 }
 
+/**
+ * strends - does @str end with @suffix?
+ * @str: string to examine
+ * @suffix: suffix to look for.
+ */
+static inline bool strends(const char *str, const char *suffix)
+{
+	size_t n = strlen(str);
+	size_t m = strlen(suffix);
+
+	return n >= m && !memcmp(str + n - m, suffix, m);
+}
+
 size_t memweight(const void *ptr, size_t bytes);
 
 /**
-- 
2.45.2