linux-ext4 - Re: [PATCH v2 03/11] ext4: reorder capability check last

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Message-ID: <kmfmwblxeav63y3noxb65pkrzw5nggbrwxblgtzt3ntag4gwrz@bz3r2vpnkozb>
Date: Tue, 4 Mar 2025 11:51:08 +0100
From: Jan Kara <jack@...e.cz>
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, 
	Theodore Ts'o <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca>, 
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v2 03/11] ext4: reorder capability check last

On Sun 02-03-25 17:06:39, Christian Göttsche wrote:
> 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>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/balloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> index 8042ad873808..c48fd36b2d74 100644
> --- a/fs/ext4/balloc.c
> +++ b/fs/ext4/balloc.c
> @@ -649,8 +649,8 @@ static int ext4_has_free_clusters(struct ext4_sb_info *sbi,
>  	/* Hm, nope.  Are (enough) root reserved clusters available? */
>  	if (uid_eq(sbi->s_resuid, current_fsuid()) ||
>  	    (!gid_eq(sbi->s_resgid, GLOBAL_ROOT_GID) && in_group_p(sbi->s_resgid)) ||
> -	    capable(CAP_SYS_RESOURCE) ||
> -	    (flags & EXT4_MB_USE_ROOT_BLOCKS)) {
> +	    (flags & EXT4_MB_USE_ROOT_BLOCKS) ||
> +	    capable(CAP_SYS_RESOURCE)) {
>  
>  		if (free_clusters >= (nclusters + dirty_clusters +
>  				      resv_clusters))
> -- 
> 2.47.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR