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Subject: Re: [PATCH v2] block: grant IOPRIO_CLASS_RT to CAP_SYS_NICE
To:     Khazhismel Kumykov <khazhy@google.com>,
        Jens Axboe <axboe@kernel.dk>
Cc:     Serge Hallyn <serge@hallyn.com>,
        Paolo Valente <paolo.valente@linaro.org>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-security-module@vger.kernel.org, linux-api@vger.kernel.org
References: <20200824221034.2170308-1-khazhy@google.com>
From:   Bart Van Assche <bvanassche@acm.org>
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Date:   Sat, 29 Aug 2020 18:00:24 -0700
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On 2020-08-24 15:10, Khazhismel Kumykov wrote:
> CAP_SYS_ADMIN is too broad, and ionice fits into CAP_SYS_NICE's grouping.
> 
> Retain CAP_SYS_ADMIN permission for backwards compatibility.
> 
> Signed-off-by: Khazhismel Kumykov <khazhy@google.com>
> ---
>  block/ioprio.c                  | 2 +-
>  include/uapi/linux/capability.h | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> v2: fix embarrassing logic mistake
> diff --git a/block/ioprio.c b/block/ioprio.c
> index 77bcab11dce5..276496246fe9 100644
> --- a/block/ioprio.c
> +++ b/block/ioprio.c
> @@ -69,7 +69,7 @@ int ioprio_check_cap(int ioprio)
>  
>  	switch (class) {
>  		case IOPRIO_CLASS_RT:
> -			if (!capable(CAP_SYS_ADMIN))
> +			if (!capable(CAP_SYS_NICE) && !capable(CAP_SYS_ADMIN))
>  				return -EPERM;
>  			/* fall through */
>  			/* rt has prio field too */
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index 395dd0df8d08..c6ca33034147 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -288,6 +288,8 @@ struct vfs_ns_cap_data {
>     processes and setting the scheduling algorithm used by another
>     process. */
>  /* Allow setting cpu affinity on other processes */
> +/* Allow setting realtime ioprio class */
> +/* Allow setting ioprio class on other processes */
>  
>  #define CAP_SYS_NICE         23

From https://www.kernel.org/doc/man-pages/linux-api-ml.html:
"all Linux kernel patches that change userspace interfaces should be CCed
to linux-api@vger.kernel.org"

So I have added the linux-api mailing list to the Cc-list. Anyway:

Reviewed-by: Bart Van Assche <bvanassche@acm.org>