drivers/char/random.c: fix boot id uniqueness race

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@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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 5e106b111d7ea866b3e797a60f7d387968886712..0c38849e279be87da0f0d850af9e4e0759e96835 100644 (file)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1258,10 +1258,15 @@ 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, "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-"
                "%02x%02x%02x%02x%02x%02x",