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authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>2012-04-12 12:49:12 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-08-15 12:04:12 -0700
commitf5a1367c1bc150e70e8db9bb6f2892e8e31648c7 (patch)
tree1a2cdb82d046008d7ad679518d19520500e8e0a5
parenta5914eb0c34cf8b2d777c3dca852b2595dec908c (diff)
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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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/char/random.c11
1 files changed, 8 insertions, 3 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 1eeb22f..5d5141f 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);