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Subject[PATCH 4.14 007/237] random: Return nbytes filled from hw RNG
Date
From: "Tobin C. Harding" <me@tobin.cc>

commit 753d433b586d1d43c487e3d660f5778c7c8d58ea upstream.

Currently the function get_random_bytes_arch() has return value 'void'.
If the hw RNG fails we currently fall back to using get_random_bytes().
This defeats the purpose of requesting random material from the hw RNG
in the first place.

There are currently no intree users of get_random_bytes_arch().

Only get random bytes from the hw RNG, make function return the number
of bytes retrieved from the hw RNG.

Acked-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 16 +++++++++-------
include/linux/random.h | 2 +-
2 files changed, 10 insertions(+), 8 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1730,26 +1730,28 @@ EXPORT_SYMBOL(del_random_ready_callback)
* key known by the NSA). So it's useful if we need the speed, but
* only if we're willing to trust the hardware manufacturer not to
* have put in a back door.
+ *
+ * Return number of bytes filled in.
*/
-void get_random_bytes_arch(void *buf, int nbytes)
+int __must_check get_random_bytes_arch(void *buf, int nbytes)
{
+ int left = nbytes;
char *p = buf;

- trace_get_random_bytes_arch(nbytes, _RET_IP_);
- while (nbytes) {
+ trace_get_random_bytes_arch(left, _RET_IP_);
+ while (left) {
unsigned long v;
- int chunk = min(nbytes, (int)sizeof(unsigned long));
+ int chunk = min_t(int, left, sizeof(unsigned long));

if (!arch_get_random_long(&v))
break;

memcpy(p, &v, chunk);
p += chunk;
- nbytes -= chunk;
+ left -= chunk;
}

- if (nbytes)
- get_random_bytes(p, nbytes);
+ return nbytes - left;
}
EXPORT_SYMBOL(get_random_bytes_arch);

--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -38,7 +38,7 @@ extern void get_random_bytes(void *buf,
extern int wait_for_random_bytes(void);
extern int add_random_ready_callback(struct random_ready_callback *rdy);
extern void del_random_ready_callback(struct random_ready_callback *rdy);
-extern void get_random_bytes_arch(void *buf, int nbytes);
+extern int __must_check get_random_bytes_arch(void *buf, int nbytes);

#ifndef MODULE
extern const struct file_operations random_fops, urandom_fops;

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