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[wily/master-next,3/7] KEYS: Fix race between key destruction and finding a keyring by name

Message ID 1449068377-21867-4-git-send-email-apw@canonical.com
State New
Headers show

Commit Message

Andy Whitcroft Dec. 2, 2015, 2:59 p.m. UTC 
From: David Howells <dhowells@redhat.com>

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@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>

(cherry picked from commit 94c4554ba07adbdde396748ee7ae01e86cf2d8d7)
CVE-2015-7872
BugLink: http://bugs.launchpad.net/bugs/1508856
Signed-off-by: Andy Whitcroft <apw@canonical.com>
---
 security/keys/gc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
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Patch

diff --git a/security/keys/gc.c b/security/keys/gc.c
index c795237..39eac1f 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -134,6 +134,10 @@  static noinline void key_gc_unused_keys(struct list_head *keys)
 		kdebug("- %u", key->serial);
 		key_check(key);
 
+		/* Throw away the key data */
+		if (key->type->destroy)
+			key->type->destroy(key);
+
 		security_key_free(key);
 
 		/* deal with the user's key tracking and quota */
@@ -148,10 +152,6 @@  static noinline void key_gc_unused_keys(struct list_head *keys)
 		if (test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 			atomic_dec(&key->user->nikeys);
 
-		/* now throw away the key memory */
-		if (key->type->destroy)
-			key->type->destroy(key);
-
 		key_user_put(key->user);
 
 		kfree(key->description);