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Message-Id: <20220211123546.474952-9-Jason@zx2c4.com>
Date: Fri, 11 Feb 2022 13:35:45 +0100
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: linux-kernel@...r.kernel.org, linux@...inikbrodowski.net
Cc: "Jason A. Donenfeld" <Jason@...c4.com>,
Theodore Ts'o <tytso@....edu>
Subject: [PATCH 8/9] random: group userspace read/write functions
This pulls all of the userspace read/write-focused functions into the
fifth labeled section.
No functional changes.
Cc: Theodore Ts'o <tytso@....edu>
Cc: Dominik Brodowski <linux@...inikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
drivers/char/random.c | 124 ++++++++++++++++++++++++++----------------
1 file changed, 76 insertions(+), 48 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index f793bd3a1325..a4229474d7fa 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1320,30 +1320,60 @@ 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)
@@ -1395,6 +1425,32 @@ static ssize_t random_write(struct file *file, const char __user *buffer,
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;
@@ -1403,7 +1459,7 @@ static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
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;
@@ -1479,34 +1535,6 @@ const struct file_operations urandom_fops = {
.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
--
2.35.0
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