* [PATCH] char random: fix boot id uniqueness race (v3)
@ 2012-02-15 18:40 Mathieu Desnoyers
2012-02-15 18:50 ` Eric Dumazet
0 siblings, 1 reply; 2+ messages in thread
From: Mathieu Desnoyers @ 2012-02-15 18:40 UTC (permalink / raw)
To: Theodore Ts'o
Cc: Matt Mackall, Eric Dumazet, Greg Kroah-Hartman, linux-kernel
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
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] char random: fix boot id uniqueness race (v3)
2012-02-15 18:40 [PATCH] char random: fix boot id uniqueness race (v3) Mathieu Desnoyers
@ 2012-02-15 18:50 ` Eric Dumazet
0 siblings, 0 replies; 2+ messages in thread
From: Eric Dumazet @ 2012-02-15 18:50 UTC (permalink / raw)
To: Mathieu Desnoyers
Cc: Theodore Ts'o, Matt Mackall, Greg Kroah-Hartman, linux-kernel
Le mercredi 15 février 2012 à 13:40 -0500, Mathieu Desnoyers a écrit :
> 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);
>
>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Thanks Mathieu !
^ permalink raw reply [flat|nested] 2+ messages in thread
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