[PATCH 3.16.y-ckt 105/107] KEYS: Fix race between key destruction and finding a keyring by name

From: Luis Henriques
Date: Mon Oct 26 2015 - 15:05:37 EST

3.16.7-ckt19 -stable review patch. If anyone has any objections, please let me know.


From: David Howells <dhowells@xxxxxxxxxx>

commit 94c4554ba07adbdde396748ee7ae01e86cf2d8d7 upstream.

There appears to be a race between:

(1) key_gc_unused_keys() which frees key->security and then calls
keyring_destroy() to unlink the name from the name list

(2) find_keyring_by_name() which calls key_permission(), thus accessing
key->security, on a key before checking to see whether the key usage is 0
(ie. the key is dead and might be cleaned up).

Fix this by calling ->destroy() before cleaning up the core key data -
including key->security.

Reported-by: Petr Matousek <pmatouse@xxxxxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Cc: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
security/keys/gc.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/security/keys/gc.c b/security/keys/gc.c
index 009d9370c8fd..38676fac7943 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -143,6 +143,10 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
kdebug("- %u", key->serial);

+ /* Throw away the key data */
+ if (key->type->destroy)
+ key->type->destroy(key);

/* deal with the user's key tracking and quota */
@@ -157,10 +161,6 @@ static noinline void key_gc_unused_keys(struct list_head *keys)
if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))

- /* now throw away the key memory */
- if (key->type->destroy)
- key->type->destroy(key);

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