This is a note to let you know that I've just added the patch titled
random: restore O_NONBLOCK support
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
random-restore-o_nonblock-support.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From cd4f24ae9404fd31fc461066e57889be3b68641b Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
Date: Thu, 8 Sep 2022 16:14:00 +0200
Subject: random: restore O_NONBLOCK support
From: Jason A. Donenfeld <Jason@xxxxxxxxx>
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@xxxxxxxxxx>
Reported-by: Zhongguohua <zhongguohua1@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Theodore Ts'o <tytso@xxxxxxx>
Cc: Andrew Lutomirski <luto@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/mem.c | 4 ++--
drivers/char/random.c | 5 +++++
2 files changed, 7 insertions(+), 2 deletions(-)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -869,8 +869,8 @@ 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
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1295,6 +1295,11 @@ static ssize_t random_read_iter(struct k
{
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;
Patches currently in stable-queue which might be from Jason@xxxxxxxxx are
queue-4.9/random-restore-o_nonblock-support.patch
queue-4.9/random-clamp-credited-irq-bits-to-maximum-mixed.patch
