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Subject[PATCH 4.20 148/183] KEYS: always initialize keyring_index_key::desc_len
Date
4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@google.com>

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 | 4 +---
security/keys/proc.c | 3 +--
security/keys/request_key.c | 1 +
security/keys/request_key_auth.c | 2 +-
4 files changed, 4 insertions(+), 6 deletions(-)

--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -661,9 +661,6 @@ static bool search_nested_keyrings(struc
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 keyri
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,
--- a/security/keys/proc.c
+++ b/security/keys/proc.c
@@ -166,8 +166,7 @@ static int proc_keys_show(struct seq_fil
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,
--- a/security/keys/request_key.c
+++ b/security/keys/request_key.c
@@ -545,6 +545,7 @@ struct key *request_key_and_link(struct
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,
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -246,7 +246,7 @@ struct key *key_get_instantiation_authke
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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