To date, all callers of randomize_range() have set the length to 0, and check for a zero return value. For the current callers, the only way to get zero returned is if end <= start. Since they are all adding a constant to the start address, this is unnecessary. We can remove a bunch of needless checks by simplifying the API to do just what everyone wants, return an address between [start, start + range). While we're here, s/get_random_int/get_random_long/. No current call site is adversely affected by get_random_int(), since all current range requests are < UINT_MAX. However, we should match caller expectations to avoid coming up short (ha!) in the future. Address generation within [start, start + range) behavior is preserved. All current callers to randomize_range() chose to use the start address if randomize_range() failed. Therefore, we simplify things by just returning the start address on error. randomize_range() will be removed once all callers have been converted over to randomize_addr(). Signed-off-by: Jason Cooper <jason@xxxxxxxxxxxxxx> --- drivers/char/random.c | 26 ++++++++++++++++++++++++++ include/linux/random.h | 1 + 2 files changed, 27 insertions(+) diff --git a/drivers/char/random.c b/drivers/char/random.c index 0158d3bff7e5..3610774bcc53 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1840,6 +1840,32 @@ randomize_range(unsigned long start, unsigned long end, unsigned long len) return PAGE_ALIGN(get_random_int() % range + start); } +/** + * randomize_addr - Generate a random, page aligned address + * @start: The smallest acceptable address the caller will take. + * @range: The size of the area, starting at @start, within which the + * random address must fall. + * + * Before page alignment, the random address generated can be any value from + * @start, to @start + @range - 1 inclusive. + * + * If @start + @range would overflow, @range is capped. + * + * Return: A page aligned address within [start, start + range). On error, + * @start is returned. + */ +unsigned long +randomize_addr(unsigned long start, unsigned long range) +{ + if (range == 0) + return start; + + if (start > ULONG_MAX - range) + range = ULONG_MAX - start; + + return PAGE_ALIGN(get_random_long() % range + start); +} + /* Interface for in-kernel drivers of true hardware RNGs. * Those devices may produce endless random bits and will be throttled * when our pool is full. diff --git a/include/linux/random.h b/include/linux/random.h index e47e533742b5..f1ca2fa4c071 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -35,6 +35,7 @@ extern const struct file_operations random_fops, urandom_fops; unsigned int get_random_int(void); unsigned long get_random_long(void); unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len); +unsigned long randomize_addr(unsigned long start, unsigned long range); u32 prandom_u32(void); void prandom_bytes(void *buf, size_t nbytes); -- 2.9.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>