From 226a07ef0a5a2dfad4cce1a5c226c4cb7370d41f Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Wed, 3 Jun 2015 15:50:35 +0200
Subject: [PATCH] lib: Clarify the return value of strnlen_user()
strnlen_user() can return a number in a range 0 to count +
sizeof(unsigned long) - 1. Clarify the comment at the top of the
function so that users don't think the function returns at most count+1.
Signed-off-by: Jan Kara <jack@suse.cz>
[ Also added commentary about preferably not using this function ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
lib/strnlen_user.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index 11649615c5050..fe9a32591c249 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -90,8 +90,15 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
* Get the size of a NUL-terminated string in user space.
*
* Returns the size of the string INCLUDING the terminating NUL.
- * If the string is too long, returns 'count+1'.
+ * If the string is too long, returns a number larger than @count. User
+ * has to check the return value against "> count".
* On exception (or invalid count), returns 0.
+ *
+ * NOTE! You should basically never use this function. There is
+ * almost never any valid case for using the length of a user space
+ * string, since the string can be changed at any time by other
+ * threads. Use "strncpy_from_user()" instead to get a stable copy
+ * of the string.
*/
long strnlen_user(const char __user *str, long count)
{
--
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