[ 80/95] drivers/char/random.c: fix boot id uniqueness race

From: Ben Hutchings
Date: Sun Sep 09 2012 - 19:32:07 EST

3.2-stable review patch. If anyone has any objections, please let me know.


From: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

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@xxxxxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Matt Mackall <mpm@xxxxxxxxxxx>
Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: Greg Kroah-Hartman <greg@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
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 54ca8b2..4ec04a7 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)
+ } 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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