lkml.org 
[lkml]   [2012]   [Feb]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] char random: fix boot id uniqueness race (v3)
The proc file /proc/sys/kernel/random/boot_id can be read concurrently
by user-space 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.

* Changelog since v1:
- boot_id_mutex is now declared within the proc_do_uuid scope.
- added explanation for memory barriers.

* Changelog since v2:
- simplify: use spinlock on all paths, suggested by Eric Dumazet.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: "Theodore Ts'o" <tytso@mit.edu>
CC: Matt Mackall <mpm@selenic.com>
CC: Eric Dumazet <eric.dumazet@gmail.com>
CC: Greg Kroah-Hartman <greg@kroah.com>
---
drivers/char/random.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

Index: linux-2.6-lttng/drivers/char/random.c
===================================================================
--- linux-2.6-lttng.orig/drivers/char/random.c
+++ linux-2.6-lttng/drivers/char/random.c
@@ -1250,10 +1250,15 @@ static int proc_do_uuid(ctl_table *table
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);

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com


\
 
 \ /
  Last update: 2012-02-15 19:43    [W:0.037 / U:0.528 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site