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KEYS: close race between key lookup and freeing

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commit a3a8784454 upstream.

When a key is being garbage collected, it's key->user would get put before
the ->destroy() callback is called, where the key is removed from it's
respective tracking structures.

This leaves a key hanging in a semi-invalid state which leaves a window open
for a different task to try an access key->user. An example is
find_keyring_by_name() which would dereference key->user for a key that is
in the process of being garbage collected (where key->user was freed but
->destroy() wasn't called yet - so it's still present in the linked list).

This would cause either a panic, or corrupt memory.

Fixes CVE-2014-9529.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Sasha Levin 2014-12-29 09:39:01 -05:00 • committed by Greg Kroah-Hartman
commit a7033e302d
1 changed files with 2 additions and 2 deletions
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4
security/keys/gc.c
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@ -201,12 +201,12 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
atomic_dec(&key->user->nikeys);
key_user_put(key->user);
/* now throw away the key memory */
if (key->type->destroy)
key->type->destroy(key);
key_user_put(key->user);
kfree(key->description);
#ifdef KEY_DEBUGGING