[PATCH] lib: Clarify the return value of strnlen_user()

[PATCH] lib: Clarify the return value of strnlen_user()

[Jan Kara]

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>
---
 lib/strnlen_user.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index fd03ae980013..77bc67222b9d 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -89,7 +89,8 @@ 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.
  */
 long strnlen_user(const char __user *str, long count)
-- 
2.1.4

Re: [PATCH] lib: Clarify the return value of strnlen_user()

[Linus Torvalds]

On Wed, Jun 3, 2015 at 6:50 AM, Jan Kara <jack@suse.cz> wrote:
> 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.

Thanks. I also extended the comment (in the same commit) on commentary
on avoiding use of this function entirely.

                 Linus