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Commit 34e9ae78 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld Committed by Greg Kroah-Hartman
Browse files

random: restore O_NONBLOCK support 



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: default avatarGuozihua <guozihua@huawei.com>
Reported-by: default avatarZhongguohua <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: default avatarJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d7950203

drivers/char/mem.c

+2 −2
Original line number Diff line number Diff line
@@ -893,8 +893,8 @@ static const struct memdev { 
#endif

	 [5] = { "zero", 0666, &zero_fops, 0 },

	 [7] = { "full", 0666, &full_fops, 0 },

	 [8] = { "random", 0666, &random_fops, 0 },

	 [9] = { "urandom", 0666, &urandom_fops, 0 },

	 [8] = { "random", 0666, &random_fops, FMODE_NOWAIT },

	 [9] = { "urandom", 0666, &urandom_fops, FMODE_NOWAIT },

#ifdef CONFIG_PRINTK

	[11] = { "kmsg", 0644, &kmsg_fops, 0 },

#endif

drivers/char/random.c

+5 −0
Original line number Diff line number Diff line
@@ -1294,6 +1294,11 @@ static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter) 
{

	int ret;



	if (!crng_ready() &&

	    ((kiocb->ki_flags & IOCB_NOWAIT) ||

	     (kiocb->ki_filp->f_flags & O_NONBLOCK)))

		return -EAGAIN;



	ret = wait_for_random_bytes();

	if (ret != 0)

		return ret;