From: Jason A. Donenfeld Jason@zx2c4.com
commit cd4f24ae9404fd31fc461066e57889be3b68641b upstream.
Prior to 5.6, when /dev/random was opened with O_NONBLOCK, it would return -EAGAIN if there was no entropy. When the pools were unified in 5.6, this was lost. The post 5.6 behavior of blocking until the pool is initialized, and ignoring O_NONBLOCK in the process, went unnoticed, with no reports about the regression received for two and a half years. However, eventually this indeed did break somebody's userspace.
So we restore the old behavior, by returning -EAGAIN if the pool is not initialized. Unlike the old /dev/random, this can only occur during early boot, after which it never blocks again.
In order to make this O_NONBLOCK behavior consistent with other expectations, also respect users reading with preadv2(RWF_NOWAIT) and similar.
Fixes: 30c08efec888 ("random: make /dev/random be almost like /dev/urandom") Reported-by: Guozihua guozihua@huawei.com Reported-by: Zhongguohua zhongguohua1@huawei.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Theodore Ts'o tytso@mit.edu Cc: Andrew Lutomirski luto@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/random.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1295,6 +1295,10 @@ static ssize_t random_read_iter(struct k { int ret;
+ if (!crng_ready() && + (kiocb->ki_filp->f_flags & O_NONBLOCK)) + return -EAGAIN; + ret = wait_for_random_bytes(); if (ret != 0) return ret;