KEYS: always initialize keyring_index_key::desc_len
authorEric Biggers <ebiggers@google.com>
Fri, 22 Feb 2019 15:36:18 +0000 (15:36 +0000)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 27 Feb 2019 09:09:00 +0000 (10:09 +0100)
commit8b4b1d7cc4d0d1cd9f45cf57e42def40c0b6c1f8
treec2417c5a108b9ae47cb3c412819d4ad2fc850144
parent390c76534de127a69b5028a82c1c28b3a6be5984
KEYS: always initialize keyring_index_key::desc_len

commit ede0fa98a900e657d1fcd80b50920efc896c1a4c upstream.

syzbot hit the 'BUG_ON(index_key->desc_len == 0);' in __key_link_begin()
called from construct_alloc_key() during sys_request_key(), because the
length of the key description was never calculated.

The problem is that we rely on ->desc_len being initialized by
search_process_keyrings(), specifically by search_nested_keyrings().
But, if the process isn't subscribed to any keyrings that never happens.

Fix it by always initializing keyring_index_key::desc_len as soon as the
description is set, like we already do in some places.

The following program reproduces the BUG_ON() when it's run as root and
no session keyring has been installed.  If it doesn't work, try removing
pam_keyinit.so from /etc/pam.d/login and rebooting.

    #include <stdlib.h>
    #include <unistd.h>
    #include <keyutils.h>

    int main(void)
    {
            int id = add_key("keyring", "syz", NULL, 0, KEY_SPEC_USER_KEYRING);

            keyctl_setperm(id, KEY_OTH_WRITE);
            setreuid(5000, 5000);
            request_key("user", "desc", "", id);
    }

Reported-by: syzbot+ec24e95ea483de0a24da@syzkaller.appspotmail.com
Fixes: b2a4df200d57 ("KEYS: Expand the capacity of a keyring")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: James Morris <james.morris@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
security/keys/keyring.c
security/keys/proc.c
security/keys/request_key.c
security/keys/request_key_auth.c