From 7707055082a7005ad94ba81e5240644db8c0324a
From: David Howells <dhowells@redhat.com>
Date:   Tue Jan 26 16:28:17 2016 +0000
Subject: [PATCH] KEYS: Only apply KEY_FLAG_KEEP to a key if a parent keyring has it set

    KEY_FLAG_KEEP should only be applied to a key if the keyring it is being
    linked into has KEY_FLAG_KEEP set.
    
    To this end, partially revert the following patch:
    
    	commit 1d6d167c2efcfe9539d9cffb1a1be9c92e39c2c0
    	Author: Mimi Zohar <zohar@linux.vnet.ibm.com>
    	Date:   Thu Jan 7 07:46:36 2016 -0500
    	KEYS: refcount bug fix
    
    to undo the change that made it unconditional (Mimi got it right the first
    time).
    
    Without undoing this change, it becomes impossible to delete, revoke or
    invalidate keys added to keyrings through __key_instantiate_and_link()
    where the keyring has itself been linked to.  To test this, run the
    following command sequence:
    
        keyctl newring foo @s
        keyctl add user a a %:foo
        keyctl unlink %user:a %:foo
        keyctl clear %:foo
    
    With the commit mentioned above the third and fourth commands fail with
    EPERM when they should succeed.
    
    Reported-by: Stephen Gallager <sgallagh@redhat.com>
    Signed-off-by: David Howells <dhowells@redhat.com>
    cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
    cc: keyrings@vger.kernel.org
    cc: stable@vger.kernel.org

diff --git a/security/keys/key.c b/security/keys/key.c
index 07a87311055c..09ef276c4bdc 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -430,7 +430,8 @@ static int __key_instantiate_and_link(struct key *key,
 
 			/* and link it into the destination keyring */
 			if (keyring) {
-				set_bit(KEY_FLAG_KEEP, &key->flags);
+				if (test_bit(KEY_FLAG_KEEP, &keyring->flags))
+					set_bit(KEY_FLAG_KEEP, &key->flags);
 
 				__key_link(key, _edit);
 			}