keys: Fix request_key() lack of Link perm check on found key

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>

diff --git a/Documentation/security/keys/core.rst b/Documentation/security/keys/core.rst
index 823d29b..82dd457 100644 (file)
--- a/Documentation/security/keys/core.rst
+++ b/Documentation/security/keys/core.rst
@@ -433,6 +433,10 @@ The main syscalls are:
      /sbin/request-key will be invoked in an attempt to obtain a key. The
      callout_info string will be passed as an argument to the program.
 
+     To link a key into the destination keyring the key must grant link
+     permission on the key to the caller and the keyring must grant write
+     permission.
+
      See also Documentation/security/keys/request-key.rst.
 
 

diff --git a/security/keys/request_key.c b/security/keys/request_key.c
index 857da65..a6543ed 100644 (file)
--- 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);