[wily/master-next 5/7] KEYS: Don't permit request_key() to construct a new keyring

[Andy Whitcroft]

From: David Howells <dhowells at redhat.com>

If request_key() is used to find a keyring, only do the search part - don't
do the construction part if the keyring was not found by the search.  We
don't really want keyrings in the negative instantiated state since the
rejected/negative instantiation error value in the payload is unioned with
keyring metadata.

Now the kernel gives an error:

	request_key("keyring", "#selinux,bdekeyring", "keyring", KEY_SPEC_USER_SESSION_KEYRING) = -1 EPERM (Operation not permitted)

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

(cherry picked from commit 911b79cde95c7da0ec02f48105358a36636b7a71)
CVE-2015-7872
BugLink: http://bugs.launchpad.net/bugs/1508856
Signed-off-by: Andy Whitcroft <apw at canonical.com>
---
 security/keys/request_key.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 486ef6f..0d62531 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -440,6 +440,9 @@ static struct key *construct_key_and_link(struct keyring_search_context *ctx,
 
 	kenter("");
 
+	if (ctx->index_key.type == &key_type_keyring)
+		return ERR_PTR(-EPERM);
+	
 	user = key_user_lookup(current_fsuid());
 	if (!user)
 		return ERR_PTR(-ENOMEM);
-- 
2.6.2