From 44e4360fa3384850d65dd36fb4e6e5f2f112709b Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers 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 Cc: "Theodore Ts'o" Cc: Matt Mackall Signed-off-by: Eric Dumazet Cc: Greg Kroah-Hartman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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); -- 2.39.2