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>
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@ -1260,10 +1260,15 @@ static int proc_do_uuid(ctl_table *table, int write,
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uuid = table->data;
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if (!uuid) {
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uuid = tmp_uuid;
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uuid[8] = 0;
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}
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if (uuid[8] == 0)
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generate_random_uuid(uuid);
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} else {
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static DEFINE_SPINLOCK(bootid_spinlock);
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spin_lock(&bootid_spinlock);
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if (!uuid[8])
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generate_random_uuid(uuid);
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spin_unlock(&bootid_spinlock);
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}
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sprintf(buf, "%pU", uuid);
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