2020-12-18 01:29:42

by Casey Schaufler

Subject: [PATCH] Smack: Handle io_uring kernel thread privileges.

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.

Suggested-by: Jens Axboe <[email protected]>
Signed-off-by: Casey Schaufler <[email protected]>
---
 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());

2020-12-21 19:58:26

by Eric W. Biederman

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

Casey Schaufler <[email protected]> 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" <[email protected]>

>
> Suggested-by: Jens Axboe <[email protected]>
> Signed-off-by: Casey Schaufler <[email protected]>
> ---
>  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());

2020-12-22 02:08:53

by Jens Axboe

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

On 12/17/20 6:12 PM, Casey Schaufler wrote:
> 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: Jens Axboe <[email protected]>

--
Jens Axboe