From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 12 Apr 2012 19:49:12 +0000 (-0700)
Subject: drivers/char/random.c: fix boot id uniqueness race
X-Git-Tag: v3.2.29~16
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=a457fb130726356e758eeadf230b21993986d0ab;p=profile%2Fivi%2Fkernel-adaptation-intel-automotive.git

drivers/char/random.c: fix boot id uniqueness race

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@efficios.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Greg Kroah-Hartman <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 631d4f6..918979f 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1391,10 +1391,15 @@ 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);