From: "Jason A. Donenfeld" Jason@zx2c4.com
commit 5209aed5137880fa229746cb521f715e55596460 upstream.
Rather than failing entirely if a copy_to_user() fails at some point, instead we should return a partial read for the amount that succeeded prior, unless none succeeded at all, in which case we return -EFAULT as before.
This makes it consistent with other reader interfaces. For example, the following snippet for /dev/zero outputs "4" followed by "1":
int fd; void *x = mmap(NULL, 4096, PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); assert(x != MAP_FAILED); fd = open("/dev/zero", O_RDONLY); assert(fd >= 0); printf("%zd\n", read(fd, x, 4)); printf("%zd\n", read(fd, x + 4095, 4)); close(fd);
This brings that same standard behavior to the various RNG reader interfaces.
While we're at it, we can streamline the loop logic a little bit.
Suggested-by: Linus Torvalds torvalds@linux-foundation.org Cc: Jann Horn jannh@google.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/random.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)
--- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -523,8 +523,7 @@ EXPORT_SYMBOL(get_random_bytes);
static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) { - ssize_t ret = 0; - size_t len; + size_t len, left, ret = 0; u32 chacha_state[CHACHA_BLOCK_SIZE / sizeof(u32)]; u8 output[CHACHA_BLOCK_SIZE];
@@ -543,37 +542,40 @@ static ssize_t get_random_bytes_user(voi * the user directly. */ if (nbytes <= CHACHA_KEY_SIZE) { - ret = copy_to_user(buf, &chacha_state[4], nbytes) ? -EFAULT : nbytes; + ret = nbytes - copy_to_user(buf, &chacha_state[4], nbytes); goto out_zero_chacha; }
- do { + for (;;) { chacha20_block(chacha_state, output); if (unlikely(chacha_state[12] == 0)) ++chacha_state[13];
len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE); - if (copy_to_user(buf, output, len)) { - ret = -EFAULT; + left = copy_to_user(buf, output, len); + if (left) { + ret += len - left; break; }
- nbytes -= len; buf += len; ret += len; + nbytes -= len; + if (!nbytes) + break;
BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0); - if (!(ret % PAGE_SIZE) && nbytes) { + if (ret % PAGE_SIZE == 0) { if (signal_pending(current)) break; cond_resched(); } - } while (nbytes); + }
memzero_explicit(output, sizeof(output)); out_zero_chacha: memzero_explicit(chacha_state, sizeof(chacha_state)); - return ret; + return ret ? ret : -EFAULT; }
/*