Commit 44e4360f authored Apr 12, 2012 by Mathieu Desnoyers Committed by Linus Torvalds Apr 12, 2012

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 <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>

parent d833049b

drivers/char/random.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -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);

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