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Subject[PATCH 4.19 102/234] random: group userspace read/write functions
Date
From: "Jason A. Donenfeld" <Jason@zx2c4.com>

commit a6adf8e7a605250b911e94793fd077933709ff9e upstream.

This pulls all of the userspace read/write-focused functions into the
fifth labeled section.

No functional changes.

Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 125 ++++++++++++++++++++++++++++++--------------------
1 file changed, 77 insertions(+), 48 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1472,30 +1472,61 @@ static void try_to_generate_entropy(void
mix_pool_bytes(&stack.now, sizeof(stack.now));
}

-static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
- loff_t *ppos)
+
+/**********************************************************************
+ *
+ * Userspace reader/writer interfaces.
+ *
+ * getrandom(2) is the primary modern interface into the RNG and should
+ * be used in preference to anything else.
+ *
+ * Reading from /dev/random has the same functionality as calling
+ * getrandom(2) with flags=0. In earlier versions, however, it had
+ * vastly different semantics and should therefore be avoided, to
+ * prevent backwards compatibility issues.
+ *
+ * Reading from /dev/urandom has the same functionality as calling
+ * getrandom(2) with flags=GRND_INSECURE. Because it does not block
+ * waiting for the RNG to be ready, it should not be used.
+ *
+ * Writing to either /dev/random or /dev/urandom adds entropy to
+ * the input pool but does not credit it.
+ *
+ * Polling on /dev/random indicates when the RNG is initialized, on
+ * the read side, and when it wants new entropy, on the write side.
+ *
+ * Both /dev/random and /dev/urandom have the same set of ioctls for
+ * adding entropy, getting the entropy count, zeroing the count, and
+ * reseeding the crng.
+ *
+ **********************************************************************/
+
+SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
+ flags)
{
- static int maxwarn = 10;
+ if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
+ return -EINVAL;

- if (!crng_ready() && maxwarn > 0) {
- maxwarn--;
- if (__ratelimit(&urandom_warning))
- pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
- current->comm, nbytes);
- }
+ /*
+ * Requesting insecure and blocking randomness at the same time makes
+ * no sense.
+ */
+ if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
+ return -EINVAL;

- return get_random_bytes_user(buf, nbytes);
-}
+ if (count > INT_MAX)
+ count = INT_MAX;

-static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes,
- loff_t *ppos)
-{
- int ret;
+ if (!(flags & GRND_INSECURE) && !crng_ready()) {
+ int ret;

- ret = wait_for_random_bytes();
- if (ret != 0)
- return ret;
- return get_random_bytes_user(buf, nbytes);
+ if (flags & GRND_NONBLOCK)
+ return -EAGAIN;
+ ret = wait_for_random_bytes();
+ if (unlikely(ret))
+ return ret;
+ }
+ return get_random_bytes_user(buf, count);
}

static __poll_t random_poll(struct file *file, poll_table *wait)
@@ -1547,6 +1578,32 @@ static ssize_t random_write(struct file
return (ssize_t)count;
}

+static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
+ loff_t *ppos)
+{
+ static int maxwarn = 10;
+
+ if (!crng_ready() && maxwarn > 0) {
+ maxwarn--;
+ if (__ratelimit(&urandom_warning))
+ pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
+ current->comm, nbytes);
+ }
+
+ return get_random_bytes_user(buf, nbytes);
+}
+
+static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes,
+ loff_t *ppos)
+{
+ int ret;
+
+ ret = wait_for_random_bytes();
+ if (ret != 0)
+ return ret;
+ return get_random_bytes_user(buf, nbytes);
+}
+
static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
{
int size, ent_count;
@@ -1555,7 +1612,7 @@ static long random_ioctl(struct file *f,

switch (cmd) {
case RNDGETENTCNT:
- /* inherently racy, no point locking */
+ /* Inherently racy, no point locking. */
if (put_user(input_pool.entropy_count, p))
return -EFAULT;
return 0;
@@ -1629,34 +1686,6 @@ const struct file_operations urandom_fop
.llseek = noop_llseek,
};

-SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
- flags)
-{
- if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
- return -EINVAL;
-
- /*
- * Requesting insecure and blocking randomness at the same time makes
- * no sense.
- */
- if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
- return -EINVAL;
-
- if (count > INT_MAX)
- count = INT_MAX;
-
- if (!(flags & GRND_INSECURE) && !crng_ready()) {
- int ret;
-
- if (flags & GRND_NONBLOCK)
- return -EAGAIN;
- ret = wait_for_random_bytes();
- if (unlikely(ret))
- return ret;
- }
- return get_random_bytes_user(buf, count);
-}
-
/********************************************************************
*
* Sysctl interface

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