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>
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@ -90,8 +90,15 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
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* Get the size of a NUL-terminated string in user space.
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* Get the size of a NUL-terminated string in user space.
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*
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*
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* Returns the size of the string INCLUDING the terminating NUL.
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* Returns the size of the string INCLUDING the terminating NUL.
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* If the string is too long, returns 'count+1'.
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* If the string is too long, returns a number larger than @count. User
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* has to check the return value against "> count".
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* On exception (or invalid count), returns 0.
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* On exception (or invalid count), returns 0.
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*
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* NOTE! You should basically never use this function. There is
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* almost never any valid case for using the length of a user space
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* string, since the string can be changed at any time by other
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* threads. Use "strncpy_from_user()" instead to get a stable copy
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* of the string.
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*/
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*/
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long strnlen_user(const char __user *str, long count)
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long strnlen_user(const char __user *str, long count)
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{
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{
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