linux-kernel - [PATCH v3 2/8] random: Add a urandom_read_nowait() for random APIs that don't warn

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Date:   Mon, 23 Dec 2019 00:20:45 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Ted Ts'o <tytso@....edu>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-man <linux-man@...r.kernel.org>,
        Stephan Mueller <smueller@...onox.de>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v3 2/8] random: Add a urandom_read_nowait() for random APIs that don't warn

/dev/random and getrandom() never warn.  Split the meat of
urandom_read() into urandom_read_nowarn() and leave the warning code
in urandom_read().

This has no effect on kernel behavior, but it makes subsequent
patches more straightforward.  It also makes the fact that
getrandom() never warns more obvious.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 drivers/char/random.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index c6252a3a4aec..7b46751772e5 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -2018,12 +2018,23 @@ random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 	return _random_read(file->f_flags & O_NONBLOCK, buf, nbytes);
 }
 
+static ssize_t
+urandom_read_nowarn(struct file *file, char __user *buf, size_t nbytes,
+		    loff_t *ppos)
+{
+	int ret;
+
+	nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));
+	ret = extract_crng_user(buf, nbytes);
+	trace_urandom_read(8 * nbytes, 0, ENTROPY_BITS(&input_pool));
+	return ret;
+}
+
 static ssize_t
 urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 {
 	unsigned long flags;
 	static int maxwarn = 10;
-	int ret;
 
 	if (!crng_ready() && maxwarn > 0) {
 		maxwarn--;
@@ -2035,10 +2046,8 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 		crng_init_cnt = 0;
 		spin_unlock_irqrestore(&primary_crng.lock, flags);
 	}
-	nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));
-	ret = extract_crng_user(buf, nbytes);
-	trace_urandom_read(8 * nbytes, 0, ENTROPY_BITS(&input_pool));
-	return ret;
+
+	return urandom_read_nowarn(file, buf, nbytes, ppos);
 }
 
 static __poll_t
@@ -2200,7 +2209,7 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
 		if (unlikely(ret))
 			return ret;
 	}
-	return urandom_read(NULL, buf, count, NULL);
+	return urandom_read_nowarn(NULL, buf, count, NULL);
 }
 
 /********************************************************************
-- 
2.23.0