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Subject: Re: [PATCH 31/34] vfs: syscall: Add fspick() to select a superblock
 for reconfiguration [ver #12]
To:     David Howells <dhowells@redhat.com>
Cc:     Al Viro <viro@ZenIV.linux.org.uk>, linux-api@vger.kernel.org,
        torvalds@linux-foundation.org, ebiederm@xmission.com,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        mszeredi@redhat.com
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From:   Alan Jenkins <alan.christopher.jenkins@gmail.com>
Message-ID: <f6f2553e-f64d-9c26-4290-baf43e5f533b@gmail.com>
Date:   Wed, 17 Oct 2018 15:31:26 +0100
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On 17/10/2018 14:20, David Howells wrote:
> David Howells <dhowells@redhat.com> wrote:
>
>> I should probably check that the picked point is actually a mountpoint.
> The root of the mount object at the path specified, that is, perhaps with
> something like the attached.
>
> David


I agree.  I'm happy to see this is using the same check as do_remount().


* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
* on it - tough luck.
*/


Thanks

Alan


> ---
> diff --git a/fs/fsopen.c b/fs/fsopen.c
> index f673e93ac456..aaaaa17a233c 100644
> --- a/fs/fsopen.c
> +++ b/fs/fsopen.c
> @@ -186,6 +186,10 @@ SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags
>   	if (ret < 0)
>   		goto err;
>   
> +	ret = -EINVAL;
> +	if (target.mnt->mnt_root != target.dentry)
> +		goto err_path;
> +
>   	fc = vfs_new_fs_context(target.dentry->d_sb->s_type, target.dentry,
>   				0, 0, FS_CONTEXT_FOR_RECONFIGURE);
>   	if (IS_ERR(fc)) {
>