linux-kernel - Re: [PATCH] autofs - fix directory and symlink access

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Date:   Fri, 15 Jun 2018 11:38:33 +0800
From:   Ian Kent <raven@...maw.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        autofs mailing list <autofs@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] autofs - fix directory and symlink access

On Fri, 2018-06-15 at 08:06 +0800, Ian Kent wrote:

Opps, missing Signed-off-by, please add it!

> Depending on how it is configured the autofs user space daemon can
> leave in use mounts mounted at exit and re-connect to them at start
> up. But for this to work best the state of the autofs file system
> needs to be left intact over the restart.
> 
> Also, at system shutdown, mounts in an autofs file system might be
> umounted exposing a mount point trigger for which subsequent access
> can lead to a hang. So recent versions of automount(8) now does its
> best to set autofs file system mounts catatonic at shutdown.
> 
> When autofs file system mounts are catatonic it's currently possible
> to create and remove directories and symlinks which can be a problem
> at restart, as described above.
> 
> So return EACCES in the directory, symlink and unlink methods if the
> autofs file system is catatonic.

Signed-off-by: Ian Kent <raven@...maw.net>

> ---
>  fs/autofs/root.c |   33 ++++++++++++++++++++++++++++++---
>  1 file changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/autofs/root.c b/fs/autofs/root.c
> index a3d414150578..782e57b911ab 100644
> --- a/fs/autofs/root.c
> +++ b/fs/autofs/root.c
> @@ -559,6 +559,13 @@ static int autofs_dir_symlink(struct inode *dir,
>  	if (!autofs_oz_mode(sbi))
>  		return -EACCES;
>  
> +	/* autofs_oz_mode() needs to allow path walks when the
> +	 * autofs mount is catatonic but the state of an autofs
> +	 * file system needs to be preserved over restarts.
> +	 */
> +	if (sbi->catatonic)
> +		return -EACCES;
> +
>  	BUG_ON(!ino);
>  
>  	autofs_clean_ino(ino);
> @@ -612,9 +619,15 @@ static int autofs_dir_unlink(struct inode *dir, struct
> dentry *dentry)
>  	struct autofs_info *ino = autofs_dentry_ino(dentry);
>  	struct autofs_info *p_ino;
>  
> -	/* This allows root to remove symlinks */
> -	if (!autofs_oz_mode(sbi) && !capable(CAP_SYS_ADMIN))
> -		return -EPERM;
> +	if (!autofs_oz_mode(sbi))
> +		return -EACCES;
> +
> +	/* autofs_oz_mode() needs to allow path walks when the
> +	 * autofs mount is catatonic but the state of an autofs
> +	 * file system needs to be preserved over restarts.
> +	 */
> +	if (sbi->catatonic)
> +		return -EACCES;
>  
>  	if (atomic_dec_and_test(&ino->count)) {
>  		p_ino = autofs_dentry_ino(dentry->d_parent);
> @@ -697,6 +710,13 @@ static int autofs_dir_rmdir(struct inode *dir, struct
> dentry *dentry)
>  	if (!autofs_oz_mode(sbi))
>  		return -EACCES;
>  
> +	/* autofs_oz_mode() needs to allow path walks when the
> +	 * autofs mount is catatonic but the state of an autofs
> +	 * file system needs to be preserved over restarts.
> +	 */
> +	if (sbi->catatonic)
> +		return -EACCES;
> +
>  	spin_lock(&sbi->lookup_lock);
>  	if (!simple_empty(dentry)) {
>  		spin_unlock(&sbi->lookup_lock);
> @@ -735,6 +755,13 @@ static int autofs_dir_mkdir(struct inode *dir,
>  	if (!autofs_oz_mode(sbi))
>  		return -EACCES;
>  
> +	/* autofs_oz_mode() needs to allow path walks when the
> +	 * autofs mount is catatonic but the state of an autofs
> +	 * file system needs to be preserved over restarts.
> +	 */
> +	if (sbi->catatonic)
> +		return -EACCES;
> +
>  	pr_debug("dentry %p, creating %pd\n", dentry, dentry);
>  
>  	BUG_ON(!ino);
> 
> --
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