Commit ede0fa98 authored by Eric Biggers's avatar Eric Biggers Committed by James Morris
Browse files

KEYS: always initialize keyring_index_key::desc_len 



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: default avatar <syzbot+ec24e95ea483de0a24da@syzkaller.appspotmail.com>
Fixes: b2a4df20 ("KEYS: Expand the capacity of a keyring")
Signed-off-by: default avatarEric Biggers <ebiggers@google.com>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarJames Morris <james.morris@microsoft.com>
parent cc1780fc

security/keys/keyring.c

+1 −3
Original line number Diff line number Diff line
@@ -661,9 +661,6 @@ static bool search_nested_keyrings(struct key *keyring, 
	BUG_ON((ctx->flags & STATE_CHECKS) == 0 ||

	       (ctx->flags & STATE_CHECKS) == STATE_CHECKS);



	if (ctx->index_key.description)

		ctx->index_key.desc_len = strlen(ctx->index_key.description);



	/* Check to see if this top-level keyring is what we are looking for

	 * and whether it is valid or not.

	 */
@@ -914,6 +911,7 @@ key_ref_t keyring_search(key_ref_t keyring, 
	struct keyring_search_context ctx = {

		.index_key.type		= type,

		.index_key.description	= description,

		.index_key.desc_len	= strlen(description),

		.cred			= current_cred(),

		.match_data.cmp		= key_default_cmp,

		.match_data.raw_data	= description,

security/keys/proc.c

+1 −2
Original line number Diff line number Diff line
@@ -165,8 +165,7 @@ static int proc_keys_show(struct seq_file *m, void *v) 
	int rc;



	struct keyring_search_context ctx = {

		.index_key.type		= key->type,

		.index_key.description	= key->description,

		.index_key		= key->index_key,

		.cred			= m->file->f_cred,

		.match_data.cmp		= lookup_user_key_possessed,

		.match_data.raw_data	= key,

security/keys/request_key.c

+1 −0
Original line number Diff line number Diff line
@@ -531,6 +531,7 @@ struct key *request_key_and_link(struct key_type *type, 
	struct keyring_search_context ctx = {

		.index_key.type		= type,

		.index_key.description	= description,

		.index_key.desc_len	= strlen(description),

		.cred			= current_cred(),

		.match_data.cmp		= key_default_cmp,

		.match_data.raw_data	= description,

security/keys/request_key_auth.c

+1 −1
Original line number Diff line number Diff line
@@ -247,7 +247,7 @@ struct key *key_get_instantiation_authkey(key_serial_t target_id) 
	struct key *authkey;

	key_ref_t authkey_ref;



	sprintf(description, "%x", target_id);

	ctx.index_key.desc_len = sprintf(description, "%x", target_id);



	authkey_ref = search_process_keyrings(&ctx);

CRA Git | Maintained and supported by SUSTech CRA and CCSE