From: Jan Kara Date: Wed, 3 Jun 2015 13:50:35 +0000 (+0200) Subject: lib: Clarify the return value of strnlen_user() X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=226a07ef0a5a2dfad4cce1a5c226c4cb7370d41f;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git 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 [ Also added commentary about preferably not using this function ] Signed-off-by: Linus Torvalds --- 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) {