linux-kernel - [PATCH 4.14 044/210] random: restore O

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20221024112958.426074294@linuxfoundation.org>
Date:   Mon, 24 Oct 2022 13:29:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Guozihua <guozihua@...wei.com>,
        Zhongguohua <zhongguohua1@...wei.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Theodore Tso <tytso@....edu>,
        Andrew Lutomirski <luto@...nel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 4.14 044/210] random: restore O_NONBLOCK support

From: Jason A. Donenfeld <Jason@...c4.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@...wei.com>
Reported-by: Zhongguohua <zhongguohua1@...wei.com>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Theodore Ts'o <tytso@....edu>
Cc: Andrew Lutomirski <luto@...nel.org>
Cc: stable@...r.kernel.org
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 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
@@ -887,8 +887,8 @@ 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
@@ -1294,6 +1294,11 @@ static ssize_t random_read_iter(struct k
 {
 	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;