linux-kernel - [PATCH 5.4 108/240] random: cleanup UUID handling

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Date:   Mon, 20 Jun 2022 14:50:09 +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,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH 5.4 108/240] random: cleanup UUID handling

From: "Jason A. Donenfeld" <Jason@...c4.com>

commit 64276a9939ff414f2f0db38036cf4e1a0a703394 upstream.

Rather than hard coding various lengths, we can use the right constants.
Strings should be `char *` while buffers should be `u8 *`. Rather than
have a nonsensical and unused maxlength, just remove it. Finally, use
snprintf instead of sprintf, just out of good hygiene.

As well, remove the old comment about returning a binary UUID via the
binary sysctl syscall. That syscall was removed from the kernel in 5.5,
and actually, the "uuid_strategy" function and related infrastructure
for even serving it via the binary sysctl syscall was removed with
894d2491153a ("sysctl drivers: Remove dead binary sysctl support") back
in 2.6.33.

Reviewed-by: Dominik Brodowski <linux@...inikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/char/random.c |   29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1656,22 +1656,25 @@ const struct file_operations urandom_fop
 static int sysctl_random_min_urandom_seed = 60;
 static int sysctl_random_write_wakeup_bits = POOL_MIN_BITS;
 static int sysctl_poolsize = POOL_BITS;
-static char sysctl_bootid[16];
+static u8 sysctl_bootid[UUID_SIZE];
 
 /*
  * This function is used to return both the bootid UUID, and random
- * UUID.  The difference is in whether table->data is NULL; if it is,
+ * UUID. The difference is in whether table->data is NULL; if it is,
  * then a new UUID is generated and returned to the user.
- *
- * If the user accesses this via the proc interface, the UUID will be
- * returned as an ASCII string in the standard UUID format; if via the
- * sysctl system call, as 16 bytes of binary data.
  */
 static int proc_do_uuid(struct ctl_table *table, int write,
 			void __user *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct ctl_table fake_table;
-	unsigned char buf[64], tmp_uuid[16], *uuid;
+	u8 tmp_uuid[UUID_SIZE], *uuid;
+	char uuid_string[UUID_STRING_LEN + 1];
+	struct ctl_table fake_table = {
+		.data = uuid_string,
+		.maxlen = UUID_STRING_LEN
+	};
+
+	if (write)
+		return -EPERM;
 
 	uuid = table->data;
 	if (!uuid) {
@@ -1686,12 +1689,8 @@ static int proc_do_uuid(struct ctl_table
 		spin_unlock(&bootid_spinlock);
 	}
 
-	sprintf(buf, "%pU", uuid);
-
-	fake_table.data = buf;
-	fake_table.maxlen = sizeof(buf);
-
-	return proc_dostring(&fake_table, write, buffer, lenp, ppos);
+	snprintf(uuid_string, sizeof(uuid_string), "%pU", uuid);
+	return proc_dostring(&fake_table, 0, buffer, lenp, ppos);
 }
 
 extern struct ctl_table random_table[];
@@ -1727,13 +1726,11 @@ struct ctl_table random_table[] = {
 	{
 		.procname	= "boot_id",
 		.data		= &sysctl_bootid,
-		.maxlen		= 16,
 		.mode		= 0444,
 		.proc_handler	= proc_do_uuid,
 	},
 	{
 		.procname	= "uuid",
-		.maxlen		= 16,
 		.mode		= 0444,
 		.proc_handler	= proc_do_uuid,
 	},