FAILED: patch "[PATCH] random: restore O_NONBLOCK support" failed to apply to 4.14-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.14-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.


thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From cd4f24ae9404fd31fc461066e57889be3b68641b Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 8 Sep 2022 16:14:00 +0200
Subject: [PATCH] random: restore O_NONBLOCK support

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>

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 32a932a065a6..5611d127363e 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -712,8 +712,8 @@ static const struct memdev {
 #endif
 	 [5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT },
 	 [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
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 79d7d4e4e582..c8cc23515568 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1347,6 +1347,11 @@ static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
 {
 	int ret;
 
+	if (!crng_ready() &&
+	    ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
+	     (kiocb->ki_filp->f_flags & O_NONBLOCK)))
+		return -EAGAIN;
+
 	ret = wait_for_random_bytes();
 	if (ret != 0)
 		return ret;