linux-kernel - Re: [PATCH] KEYS: put keyring if install_session_keyring_to

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Date:   Mon, 03 Apr 2017 16:42:05 +0100
From:   David Howells <dhowells@...hat.com>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     dhowells@...hat.com, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH] KEYS: put keyring if install_session_keyring_to_cred() fails

Eric Biggers <ebiggers3@...il.com> wrote:

> +error3:
> +	key_put(keyring);
>  error2:
>  	mutex_unlock(&key_session_mutex);

I would prefer the put to be outside of the locked section.  How about the
attached instead?

David
---
commit 5f9e6fc4fdbbf9ada9bd03640b1c3ca50a3e5415
Author: Eric Biggers <ebiggers@...gle.com>
Date:   Sat Apr 1 11:54:16 2017 -0700

    KEYS: put keyring if install_session_keyring_to_cred() fails
    
    In join_session_keyring(), if install_session_keyring_to_cred() were to
    fail, we would leak the keyring reference, just like in the bug fixed by
    commit 23567fd052a9 ("KEYS: Fix keyring ref leak in
    join_session_keyring()").  Fortunately this cannot happen currently, but
    we really should be more careful.  Do this by adding and using a new
    error label at which the keyring reference is dropped.
    
    Signed-off-by: Eric Biggers <ebiggers@...gle.com>
    Signed-off-by: David Howells <dhowells@...hat.com>

diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 44451af828c0..8e98e5d1b5fb 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -793,21 +793,20 @@ long join_session_keyring(const char *name)
 			KEY_ALLOC_IN_QUOTA, NULL, NULL);
 		if (IS_ERR(keyring)) {
 			ret = PTR_ERR(keyring);
-			goto error2;
+			goto error_unlock_no_keyring;
 		}
 	} else if (IS_ERR(keyring)) {
 		ret = PTR_ERR(keyring);
-		goto error2;
+		goto error_unlock_no_keyring;
 	} else if (keyring == new->session_keyring) {
-		key_put(keyring);
 		ret = 0;
-		goto error2;
+		goto error_unlock;
 	}
 
 	/* we've got a keyring - now to install it */
 	ret = install_session_keyring_to_cred(new, keyring);
 	if (ret < 0)
-		goto error2;
+		goto error_unlock;
 
 	commit_creds(new);
 	mutex_unlock(&key_session_mutex);
@@ -817,8 +816,11 @@ long join_session_keyring(const char *name)
 okay:
 	return ret;
 
-error2:
+error_unlock_no_keyring:
+	keyring = NULL;
+error_unlock:
 	mutex_unlock(&key_session_mutex);
+	key_put(keyring);
 error:
 	abort_creds(new);
 	return ret;