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-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)
{