linux-kernel - Re: [PATCH 2/2] fs/kernfs/dir: obey S

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Message-ID: <ZWoRA52jPacJCiqs@slm.duckdns.org>
Date:   Fri, 1 Dec 2023 06:59:47 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Max Kellermann <max.kellermann@...os.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fs/kernfs/dir: obey S_ISGID

On Fri, Dec 01, 2023 at 01:56:38PM +0100, Max Kellermann wrote:
> Handling of S_ISGID is usually done by inode_init_owner() in all other
> filesystems, but kernfs doesn't use that function.  In kernfs, struct
> kernfs_node is the primary data structure, and struct inode is only
> created from it on demand.  Therefore, inode_init_owner() can't be
> used and we need to imitate its behavior.
> 
> S_ISGID support is useful for the cgroup filesystem; it allows
> subtrees managed by an unprivileged process to retain a certain owner
> gid, which then enables sharing access to the subtree with another
> unprivileged process.
> 
> Signed-off-by: Max Kellermann <max.kellermann@...os.com>

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun