Re: [PATCH v3] KEYS: Fix key_reject_and_link() race with keyring restriction

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Oct 08, 2026 at 02:03:51PM -0700, adrimg3196@gmail.com wrote:
> 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.
> 
> Move the check to after __key_link_lock(), so it is done under the
> semaphore, matching the pattern used in __key_create_or_update().
> 
> Fixes: 5ac7eace2d00 ("KEYS: Add a facility to restrict new links into
> a keyring")
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> Signed-off-by: Adrian Martinez <adrimg3196@gmail.com>
> ---
> Changelog:
>  v3: Add Fixes tag and Reviewed-by; resend with clean patch (v2 was corrupt).
>  v2: Resend with full patch (v1 arrived without the diff).
> 
>  security/keys/key.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/security/keys/key.c b/security/keys/key.c
> index 1234567..abcdefg 100644
> --- a/security/keys/key.c
> +++ b/security/keys/key.c
> @@ -590,10 +590,17 @@ 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.
> +			 */
> +			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);

Thank you!

I applied this.


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

Br, Jarkko