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Subject: [RFC PATCH 21/27] keys: Fix request_key() lack of Link perm check
 on found key
From:   David Howells <dhowells@redhat.com>
To:     keyrings@vger.kernel.org, trond.myklebust@hammerspace.com,
        sfrench@samba.org
Cc:     linux-security-module@vger.kernel.org, linux-nfs@vger.kernel.org,
        linux-cifs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        rgb@redhat.com, dhowells@redhat.com, linux-kernel@vger.kernel.org
Date:   Fri, 15 Feb 2019 16:11:22 +0000
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The request_key() syscall allows a process to gain access to the 'possessor'
permits of any key that grants it Search permission by virtue of request_key()
not checking whether a key it finds grants Link permission to the caller.

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

 security/keys/request_key.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index ab1f6de9e623..10244b6fbf5d 100644
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -564,6 +564,16 @@ struct key *request_key_and_link(struct key_type *type,
 	key_ref = search_process_keyrings(&ctx);
 
 	if (!IS_ERR(key_ref)) {
+		if (dest_keyring) {
+			ret = key_task_permission(key_ref, current_cred(),
+						  KEY_NEED_LINK);
+			if (ret < 0) {
+				key_ref_put(key_ref);
+				key = ERR_PTR(ret);
+				goto error_free;
+			}
+		}
+
 		key = key_ref_to_ptr(key_ref);
 		if (dest_keyring) {
 			ret = key_link(dest_keyring, key);