[RFC PATCH 21/27] keys: Fix request_key() lack of Link perm check on found key

[David Howells]

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 <dhowe...@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);