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Commit 226a07ef authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
Browse files

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: default avatarJan Kara <jack@suse.cz>
[ Also added commentary about preferably not using this function ]
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8cd9234c

lib/strnlen_user.c

+8 −1
Original line number Diff line number Diff line
@@ -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)

{