[PATCH 3.2 59/60] KEYS: Fix race between key destruction and finding a keyring by name

From: Ben Hutchings
Date: Sat Nov 14 2015 - 21:18:40 EST

3.2.73-rc1 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>
[carnil: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
security/keys/gc.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -172,6 +172,10 @@ static noinline void key_gc_unused_key(s

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

/* deal with the user's key tracking and quota */
@@ -186,10 +190,6 @@ static noinline void key_gc_unused_key(s
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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