[RFC patch 1/6] random: Simplify API for random address requests

Jason Cooper
2016-07-26T03:05:23Z

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 < MAX_UINT. However, we should match caller expectations
to avoid coming up short (ha!) in the future.

Signed-off-by: Jason Cooper <jason@lakedaemon.net>
---
drivers/char/random.c | 17 ++++-------------
include/linux/random.h | 2 +-
2 files changed, 5 insertions(+), 14 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0158d3bff7e5..1251cb2cbab2 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1822,22 +1822,13 @@ unsigned long get_random_long(void)
EXPORT_SYMBOL(get_random_long);

/*
- * randomize_range() returns a start address such that
- *
- * [...... <range> .....]
- * start end
- *
- * a <range> with size "len" starting at the return value is inside in the
- * area defined by [start, end], but is otherwise randomized.
+ * randomize_addr() returns a page aligned address within [start, start +
+ * range]
*/
unsigned long
-randomize_range(unsigned long start, unsigned long end, unsigned long len)
+randomize_addr(unsigned long start, unsigned long range)
{
- unsigned long range = end - len - start;
-
- if (end <= start + len)
- return 0;
- return PAGE_ALIGN(get_random_int() % range + start);
+ return PAGE_ALIGN(get_random_long() % range + start);
}

/* Interface for in-kernel drivers of true hardware RNGs.
diff --git a/include/linux/random.h b/include/linux/random.h
index e47e533742b5..1ad877a98186 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -34,7 +34,7 @@ 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