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

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Message-Id: <20160726030201.6775-1-jason@lakedaemon.net>
Date:	Tue, 26 Jul 2016 03:01:55 +0000
From:	Jason Cooper <jason@...edaemon.net>
To:	william.c.roberts@...el.com, linux-mm@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Cc:	Jason Cooper <jason@...edaemon.net>, linux@....linux.org.uk,
	akpm@...ux-foundation.org, keescook@...omium.org, tytso@....edu,
	arnd@...db.de, gregkh@...uxfoundation.org, catalin.marinas@....com,
	will.deacon@....com, ralf@...ux-mips.org, benh@...nel.crashing.org,
	paulus@...ba.org, mpe@...erman.id.au, davem@...emloft.net,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, viro@...iv.linux.org.uk, nnk@...gle.com,
	jeffv@...gle.com, alyzyn@...roid.com, dcashman@...roid.com
Subject: [RFC patch 1/6] random: Simplify API for random address requests

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@...edaemon.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