From: Eric Biggers ebiggers@google.com

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 ---

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(-)

diff --git a/security/keys/keyring.c b/security/keys/keyring.c index eadebb92986a..f81372f53dd7 100644 --- a/security/keys/keyring.c +++ b/security/keys/keyring.c @@ -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, diff --git a/security/keys/proc.c b/security/keys/proc.c index d2b802072693..78ac305d715e 100644 --- a/security/keys/proc.c +++ b/security/keys/proc.c @@ -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, diff --git a/security/keys/request_key.c b/security/keys/request_key.c index 3f56a312dd35..7a0c6b666ff0 100644 --- a/security/keys/request_key.c +++ b/security/keys/request_key.c @@ -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, diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c index afc304e8b61e..bda6201c6c45 100644 --- a/security/keys/request_key_auth.c +++ b/security/keys/request_key_auth.c @@ -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);