linux-kernel - [v2.6.34-stable 150/165] drivers/char/random.c: fix boot id uniqueness race

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Message-ID: <1345060109-9187-151-git-send-email-paul.gortmaker@windriver.com>
Date:	Wed, 15 Aug 2012 15:48:14 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	<stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	"Theodore Ts'o" <tytso@....edu>, Matt Mackall <mpm@...enic.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Greg Kroah-Hartman <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [v2.6.34-stable 150/165] drivers/char/random.c: fix boot id uniqueness race

From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 44e4360fa3384850d65dd36fb4e6e5f2f112709b upstream.

/proc/sys/kernel/random/boot_id can be read concurrently by userspace
processes.  If two (or more) user-space processes concurrently read
boot_id when sysctl_bootid is not yet assigned, a race can occur making
boot_id differ between the reads.  Because the whole point of the boot id
is to be unique across a kernel execution, fix this by protecting this
operation with a spinlock.

Given that this operation is not frequently used, hitting the spinlock
on each call should not be an issue.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: "Theodore Ts'o" <tytso@....edu>
Cc: Matt Mackall <mpm@...enic.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Cc: Greg Kroah-Hartman <greg@...ah.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 drivers/char/random.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index fce764d..1b3544d 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1251,10 +1251,15 @@ static int proc_do_uuid(ctl_table *table, int write,
 	uuid = table->data;
 	if (!uuid) {
 		uuid = tmp_uuid;
-		uuid[8] = 0;
-	}
-	if (uuid[8] == 0)
 		generate_random_uuid(uuid);
+	} else {
+		static DEFINE_SPINLOCK(bootid_spinlock);
+
+		spin_lock(&bootid_spinlock);
+		if (!uuid[8])
+			generate_random_uuid(uuid);
+		spin_unlock(&bootid_spinlock);
+	}
 
 	sprintf(buf, "%pU", uuid);
 
-- 
1.7.12.rc2

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