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author | Jason A. Donenfeld <Jason@zx2c4.com> | 2022-04-07 22:23:08 +0300 |
---|---|---|
committer | Jason A. Donenfeld <Jason@zx2c4.com> | 2022-04-13 14:58:57 +0300 |
commit | 5209aed5137880fa229746cb521f715e55596460 (patch) | |
tree | 887fc3a4c4269b00f739e17e379926ee77063fee /drivers | |
parent | a19944809fe9942e6a96292490717904d0690c21 (diff) | |
download | linux-5209aed5137880fa229746cb521f715e55596460.tar.xz |
random: allow partial reads if later user copies fail
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>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/char/random.c | 22 |
1 files changed, 12 insertions, 10 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c index e15063d61460..df43c5060f00 100644 --- 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_STATE_WORDS]; u8 output[CHACHA_BLOCK_SIZE]; @@ -543,37 +542,40 @@ static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) * 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; } /* |