random: convert to using fops->read_iter()

This is a pre-requisite to wiring up splice() again for the random
and urandom drivers. It also allows us to remove the INT_MAX check in
getrandom(), because import_single_range() applies capping internally.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
[Jason: rewrote get_random_bytes_user() to simplify and also incorporate
 additional suggestions from Al.]
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0958fa9..34b7737 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -397,13 +397,13 @@ void get_random_bytes(void *buf, size_t len)
 }
 EXPORT_SYMBOL(get_random_bytes);
 
-static ssize_t get_random_bytes_user(void __user *ubuf, size_t len)
+static ssize_t get_random_bytes_user(struct iov_iter *iter)
 {
-       size_t block_len, left, ret = 0;
        u32 chacha_state[CHACHA_STATE_WORDS];
-       u8 output[CHACHA_BLOCK_SIZE];
+       u8 block[CHACHA_BLOCK_SIZE];
+       size_t ret = 0, copied;
 
-       if (!len)
+       if (unlikely(!iov_iter_count(iter)))
                return 0;
 
        /*
@@ -417,30 +417,22 @@ static ssize_t get_random_bytes_user(void __user *ubuf, size_t len)
         * use chacha_state after, so we can simply return those bytes to
         * the user directly.
         */
-       if (len <= CHACHA_KEY_SIZE) {
-               ret = len - copy_to_user(ubuf, &chacha_state[4], len);
+       if (iov_iter_count(iter) <= CHACHA_KEY_SIZE) {
+               ret = copy_to_iter(&chacha_state[4], CHACHA_KEY_SIZE, iter);
                goto out_zero_chacha;
        }
 
        for (;;) {
-               chacha20_block(chacha_state, output);
+               chacha20_block(chacha_state, block);
                if (unlikely(chacha_state[12] == 0))
                        ++chacha_state[13];
 
-               block_len = min_t(size_t, len, CHACHA_BLOCK_SIZE);
-               left = copy_to_user(ubuf, output, block_len);
-               if (left) {
-                       ret += block_len - left;
-                       break;
-               }
-
-               ubuf += block_len;
-               ret += block_len;
-               len -= block_len;
-               if (!len)
+               copied = copy_to_iter(block, sizeof(block), iter);
+               ret += copied;
+               if (!iov_iter_count(iter) || copied != sizeof(block))
                        break;
 
-               BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0);
+               BUILD_BUG_ON(PAGE_SIZE % sizeof(block) != 0);
                if (ret % PAGE_SIZE == 0) {
                        if (signal_pending(current))
                                break;
@@ -448,7 +440,7 @@ static ssize_t get_random_bytes_user(void __user *ubuf, size_t len)
                }
        }
 
-       memzero_explicit(output, sizeof(output));
+       memzero_explicit(block, sizeof(block));
 out_zero_chacha:
        memzero_explicit(chacha_state, sizeof(chacha_state));
        return ret ? ret : -EFAULT;
@@ -1248,6 +1240,10 @@ static void __cold try_to_generate_entropy(void)
 
 SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
 {
+       struct iov_iter iter;
+       struct iovec iov;
+       int ret;
+
        if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
                return -EINVAL;
 
@@ -1258,19 +1254,18 @@ SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags
        if ((flags & (GRND_INSECURE | GRND_RANDOM)) == (GRND_INSECURE | GRND_RANDOM))
                return -EINVAL;
 
-       if (len > INT_MAX)
-               len = INT_MAX;
-
        if (!crng_ready() && !(flags & GRND_INSECURE)) {
-               int ret;
-
                if (flags & GRND_NONBLOCK)
                        return -EAGAIN;
                ret = wait_for_random_bytes();
                if (unlikely(ret))
                        return ret;
        }
-       return get_random_bytes_user(ubuf, len);
+
+       ret = import_single_range(READ, ubuf, len, &iov, &iter);
+       if (unlikely(ret))
+               return ret;
+       return get_random_bytes_user(&iter);
 }
 
 static __poll_t random_poll(struct file *file, poll_table *wait)
@@ -1314,8 +1309,7 @@ static ssize_t random_write(struct file *file, const char __user *ubuf,
        return (ssize_t)len;
 }
 
-static ssize_t urandom_read(struct file *file, char __user *ubuf,
-                           size_t len, loff_t *ppos)
+static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
 {
        static int maxwarn = 10;
 
@@ -1331,23 +1325,22 @@ static ssize_t urandom_read(struct file *file, char __user *ubuf,
                        ++urandom_warning.missed;
                else if (ratelimit_disable || __ratelimit(&urandom_warning)) {
                        --maxwarn;
-                       pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
-                                 current->comm, len);
+                       pr_notice("%s: uninitialized urandom read (%zu bytes read)\n",
+                                 current->comm, iov_iter_count(iter));
                }
        }
 
-       return get_random_bytes_user(ubuf, len);
+       return get_random_bytes_user(iter);
 }
 
-static ssize_t random_read(struct file *file, char __user *ubuf,
-                          size_t len, loff_t *ppos)
+static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
 {
        int ret;
 
        ret = wait_for_random_bytes();
        if (ret != 0)
                return ret;
-       return get_random_bytes_user(ubuf, len);
+       return get_random_bytes_user(iter);
 }
 
 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
@@ -1409,7 +1402,7 @@ static int random_fasync(int fd, struct file *filp, int on)
 }
 
 const struct file_operations random_fops = {
-       .read = random_read,
+       .read_iter = random_read_iter,
        .write = random_write,
        .poll = random_poll,
        .unlocked_ioctl = random_ioctl,
@@ -1419,7 +1412,7 @@ const struct file_operations random_fops = {
 };
 
 const struct file_operations urandom_fops = {
-       .read = urandom_read,
+       .read_iter = urandom_read_iter,
        .write = random_write,
        .unlocked_ioctl = random_ioctl,
        .compat_ioctl = compat_ptr_ioctl,