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authorJan Kara <jack@suse.cz>2015-06-03 15:50:35 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2015-06-03 08:00:22 -0700
commit226a07ef0a5a2dfad4cce1a5c226c4cb7370d41f (patch)
tree7b957c610ea1df9e099173ac29e84ef7ca6856b4
parent8cd9234c64c584432f6992fe944ca9e46ca8ea76 (diff)
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>
-rw-r--r--lib/strnlen_user.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index 11649615c505..fe9a32591c24 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)
{