linux-kernel - Re: [PATCH] Smack: Handle io_uring kernel thread privileges.

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Message-ID: <877dpbkk8a.fsf@x220.int.ebiederm.org>
Date:   Mon, 21 Dec 2020 13:55:01 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Casey Schaufler <casey@...aufler-ca.com>
Cc:     "SMACK-discuss\@lists.01.org" <SMACK-discuss@...ts.01.org>,
        Linux Security Module list 
        <linux-security-module@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Smack: Handle io_uring kernel thread privileges.

Casey Schaufler <casey@...aufler-ca.com> writes:

> Smack assumes that kernel threads are privileged for smackfs
> operations. This was necessary because the credential of the
> kernel thread was not related to a user operation. With io_uring
> the credential does reflect a user's rights and can be used.

Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>

>
> Suggested-by: Jens Axboe <axboe@...nel.dk>
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> ---
>  security/smack/smack_access.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
> index efe2406a3960..7eabb448acab 100644
> --- a/security/smack/smack_access.c
> +++ b/security/smack/smack_access.c
> @@ -688,9 +688,10 @@ bool smack_privileged_cred(int cap, const struct cred *cred)
>  bool smack_privileged(int cap)
>  {
>  	/*
> -	 * All kernel tasks are privileged
> +	 * Kernel threads may not have credentials we can use.
> +	 * The io_uring kernel threads do have reliable credentials.
>  	 */
> -	if (unlikely(current->flags & PF_KTHREAD))
> +	if ((current->flags & (PF_KTHREAD | PF_IO_WORKER)) == PF_KTHREAD)
>  		return true;
>  
>  	return smack_privileged_cred(cap, current_cred());