Commit 4b08addb authored by Eric Biggers's avatar Eric Biggers Committed by Greg Kroah-Hartman

KEYS: always initialize keyring_index_key::desc_len

commit ede0fa98 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 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);

Fixes: b2a4df20 ("KEYS: Expand the capacity of a keyring")
Signed-off-by: 's avatarEric Biggers <>
Signed-off-by: 's avatarDavid Howells <>
Signed-off-by: 's avatarJames Morris <>
Signed-off-by: 's avatarGreg Kroah-Hartman <>
parent cfc7fbe6
......@@ -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,
......@@ -166,8 +166,7 @@ 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,
......@@ -545,6 +545,7 @@ 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,
......@@ -246,7 +246,7 @@ 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);
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