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SubjectRe: [PATCH] KEYS: always initialize keyring_index_key::desc_len
On Fri, Nov 02, 2018 at 04:15:10PM -0700, Eric Biggers wrote:
> 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")
> Cc: <stable@vger.kernel.org> # v3.13+
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
> security/keys/keyring.c | 4 +---
> security/keys/proc.c | 1 +
> security/keys/request_key.c | 1 +
> security/keys/request_key_auth.c | 2 +-
> 4 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/security/keys/keyring.c b/security/keys/keyring.c
> index 41bcf57e96f2..99a55145ddcd 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 5af2934965d8..909f6c5270a1 100644
> --- a/security/keys/proc.c
> +++ b/security/keys/proc.c
> @@ -168,6 +168,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
> struct keyring_search_context ctx = {
> .index_key.type = key->type,
> .index_key.description = key->description,
> + .index_key.desc_len = strlen(key->description),
> .cred = m->file->f_cred,
> .match_data.cmp = lookup_user_key_possessed,
> .match_data.raw_data = key,

It's actually possible to just set '.index_key = key->index_key' here.
I'll send v2 with that instead.

- Eric

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