Re: [PATCH v2] KEYS: Fix key_reject_and_link() race with keyring restriction

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Oct 08, 2026 at 11:18:02AM -0700, adrimg3196@gmail.com wrote:
> Jarkko, you're right — v1 arrived without the diff. Here's v2 with the
> full patch.

And it would not be your fault if it had gone to my PR as I have
ultimate responsibility for that part.

Anyhow, put side-notes under '---'. It's a good place for these
as it does not get pulled into the commit log.

For single-patch submission it is also great place to maintain
changelog.

> 
> The restrict_link check in key_reject_and_link() is done before taking
> the keyring semaphore, racing with a concurrent keyring_restrict()
> that installs the restriction while holding the semaphore in write
> mode.
> 
> This is the same pattern that commit dd3ea3fc ("KEYS: Fix add_key()
> race with keyring restriction") just fixed in __key_create_or_update()
> by moving the restrict_link snapshot to after the semaphore is taken.
> 
> Move the check under __key_link_lock() so a restriction installed
> concurrently cannot be bypassed when linking a negative key.
> 

Fixes: 5ac7eace2d00 ("KEYS: Add a facility to restrict new links into a keyring")o
> Signed-off-by: Adrian Martinez <adrimg3196@gmail.com>
> ---
Here.
>  security/keys/key.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> --- a/security/keys/key.c
> +++ b/security/keys/key.c
> @@ -588,10 +588,17 @@ int key_reject_and_link(struct key *key,
>  	ret = -EBUSY;
> 
>  	if (keyring) {
> -		if (keyring->restrict_link)
> -			return -EPERM;
> -
>  		link_ret = __key_link_lock(keyring, &key->index_key);
>  		if (link_ret == 0) {
> +			/*
> +			 * Check the restriction under the keyring semaphore.
> +			 * keyring_restrict() installs it while holding the
> +			 * semaphore, so testing it beforehand races with a
> +			 * concurrent restriction install (cf. the fix for
> +			 * __key_create_or_update()).
> +			 */
> +			if (keyring->restrict_link) {
> +				__key_link_end(keyring, &key->index_key, edit);
> +				return -EPERM;
> +			}
>  			link_ret = __key_link_begin(keyring, &key->index_key, &edit);
>  			if (link_ret < 0)
>  				__key_link_end(keyring, &key->index_key, edit);


Looks good to me, thank you.

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

Br, Jarkko