From 44e4360fa3384850d65dd36fb4e6e5f2f112709b Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 12 Apr 2012 12:49:12 -0700
Subject: [PATCH] drivers/char/random.c: fix boot id uniqueness race
/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>
---
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 54ca8b23cde3..4ec04a754733 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1260,10 +1260,15 @@ 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);
--
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