linux-kernel - Re: [PATCH v2 06/11] ubifs: reorder capability check last

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Message-ID: <a9257803-c5cd-bb83-21b6-a8b152c943e6@huawei.com>
Date: Mon, 3 Mar 2025 21:49:17 +0800
From: Zhihao Cheng <chengzhihao1@...wei.com>
To: <cgzones@...glemail.com>
CC: Serge Hallyn <serge@...lyn.com>, Jan Kara <jack@...e.com>, Julia Lawall
	<Julia.Lawall@...ia.fr>, Nicolas Palix <nicolas.palix@...g.fr>,
	<linux-kernel@...r.kernel.org>, <linux-security-module@...r.kernel.org>,
	<cocci@...ia.fr>, Richard Weinberger <richard@....at>,
	<linux-mtd@...ts.infradead.org>
Subject: Re: [PATCH v2 06/11] ubifs: reorder capability check last

在 2025/3/3 0:06, Christian Göttsche 写道:
> From: Christian Göttsche <cgzones@...glemail.com>
> 
> capable() calls refer to enabled LSMs whether to permit or deny the
> request.  This is relevant in connection with SELinux, where a
> capability check results in a policy decision and by default a denial
> message on insufficient permission is issued.
> It can lead to three undesired cases:
>    1. A denial message is generated, even in case the operation was an
>       unprivileged one and thus the syscall succeeded, creating noise.
>    2. To avoid the noise from 1. the policy writer adds a rule to ignore
>       those denial messages, hiding future syscalls, where the task
>       performs an actual privileged operation, leading to hidden limited
>       functionality of that task.
>    3. To avoid the noise from 1. the policy writer adds a rule to permit
>       the task the requested capability, while it does not need it,
>       violating the principle of least privilege.
> 
> Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
> Reviewed-by: Serge Hallyn <serge@...lyn.com>
> Acked-by: Richard Weinberger <richard@....at>
> ---
> v2: split into two patches for each subsystem
> ---
>   fs/ubifs/budget.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)

Reviewed-by: Zhihao Cheng <chengzhihao1@...wei.com>
> 
> diff --git a/fs/ubifs/budget.c b/fs/ubifs/budget.c
> index d76eb7b39f56..6137aeadec3f 100644
> --- a/fs/ubifs/budget.c
> +++ b/fs/ubifs/budget.c
> @@ -256,8 +256,9 @@ long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
>    */
>   static int can_use_rp(struct ubifs_info *c)
>   {
> -	if (uid_eq(current_fsuid(), c->rp_uid) || capable(CAP_SYS_RESOURCE) ||
> -	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)))
> +	if (uid_eq(current_fsuid(), c->rp_uid) ||
> +	    (!gid_eq(c->rp_gid, GLOBAL_ROOT_GID) && in_group_p(c->rp_gid)) ||
> +	    capable(CAP_SYS_RESOURCE))
>   		return 1;
>   	return 0;
>   }
>