Re: [PATCH 3/4] autofs - make mountpoint checks namespace aware

[Eric W. Biederman]

Ian Kent <raven@xxxxxxxxxx> writes:

> If an automount mount is clone(2)ed into a file system that is
> propagation private, when it later expires in the originating
> namespace subsequent calls to autofs ->d_automount() for that
> dentry in the original namespace will return ELOOP until the
> mount is manually umounted in the cloned namespace.
>
> In the same way, if an autofs mount is triggered by automount(8)
> running within a container the dentry will be seen as mounted in
> the root init namespace and calls to ->d_automount() in that namespace
> will return ELOOP until the mount is umounted within the container.
>
> Also, have_submounts() can return an incorect result when a mount
> exists in a namespace other than the one being checked.

Overall this appears to be a fairly reasonable set of changes.  It does
increase the expense when an actual mount point is encountered, but if
these are the desired some increase in cost when a dentry is a
mountpoint is unavoidable.

May I ask the motiviation for this set of changes?  Reading through the
changes I don't grasp why we want to change the behavior of autofs.
What problem is being solved?  What are the benefits?

Eric

> Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Omar Sandoval <osandov@xxxxxxxxxxx>
> ---
>  fs/autofs4/dev-ioctl.c |    2 +-
>  fs/autofs4/expire.c    |    4 ++--
>  fs/autofs4/root.c      |   30 +++++++++++++++---------------
>  fs/autofs4/waitq.c     |    2 +-
>  4 files changed, 19 insertions(+), 19 deletions(-)
>
> diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
> index c7fcc74..0024e25 100644
> --- a/fs/autofs4/dev-ioctl.c
> +++ b/fs/autofs4/dev-ioctl.c
> @@ -564,7 +564,7 @@ static int autofs_dev_ioctl_ismountpoint(struct file *fp,
>  
>  		devid = new_encode_dev(dev);
>  
> -		err = have_submounts(path.dentry);
> +		err = have_local_submounts(path.dentry);
>  
>  		if (follow_down_one(&path))
>  			magic = path.dentry->d_sb->s_magic;
> diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
> index d8e6d42..7cc34ef 100644
> --- a/fs/autofs4/expire.c
> +++ b/fs/autofs4/expire.c
> @@ -236,7 +236,7 @@ static int autofs4_tree_busy(struct vfsmount *mnt,
>  		 * count for the autofs dentry.
>  		 * If the fs is busy update the expiry counter.
>  		 */
> -		if (d_mountpoint(p)) {
> +		if (is_local_mountpoint(p)) {
>  			if (autofs4_mount_busy(mnt, p)) {
>  				top_ino->last_used = jiffies;
>  				dput(p);
> @@ -280,7 +280,7 @@ static struct dentry *autofs4_check_leaves(struct vfsmount *mnt,
>  	while ((p = get_next_positive_dentry(p, parent))) {
>  		pr_debug("dentry %p %pd\n", p, p);
>  
> -		if (d_mountpoint(p)) {
> +		if (is_local_mountpoint(p)) {
>  			/* Can we umount this guy */
>  			if (autofs4_mount_busy(mnt, p))
>  				continue;
> diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
> index fa84bb8..4150ad6 100644
> --- a/fs/autofs4/root.c
> +++ b/fs/autofs4/root.c
> @@ -123,7 +123,7 @@ static int autofs4_dir_open(struct inode *inode, struct file *file)
>  	 * it.
>  	 */
>  	spin_lock(&sbi->lookup_lock);
> -	if (!d_mountpoint(dentry) && simple_empty(dentry)) {
> +	if (!is_local_mountpoint(dentry) && simple_empty(dentry)) {
>  		spin_unlock(&sbi->lookup_lock);
>  		return -ENOENT;
>  	}
> @@ -370,28 +370,28 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
>  
>  	/*
>  	 * If the dentry is a symlink it's equivalent to a directory
> -	 * having d_mountpoint() true, so there's no need to call back
> -	 * to the daemon.
> +	 * having is_local_mountpoint() true, so there's no need to
> +	 * call back to the daemon.
>  	 */
>  	if (d_really_is_positive(dentry) && d_is_symlink(dentry)) {
>  		spin_unlock(&sbi->fs_lock);
>  		goto done;
>  	}
>  
> -	if (!d_mountpoint(dentry)) {
> +	if (!is_local_mountpoint(dentry)) {
>  		/*
>  		 * It's possible that user space hasn't removed directories
>  		 * after umounting a rootless multi-mount, although it
> -		 * should. For v5 have_submounts() is sufficient to handle
> -		 * this because the leaves of the directory tree under the
> -		 * mount never trigger mounts themselves (they have an autofs
> -		 * trigger mount mounted on them). But v4 pseudo direct mounts
> -		 * do need the leaves to trigger mounts. In this case we
> -		 * have no choice but to use the list_empty() check and
> -		 * require user space behave.
> +		 * should. For v5 have_local_submounts() is sufficient to
> +		 * handle this because the leaves of the directory tree under
> +		 * the mount never trigger mounts themselves (they have an
> +		 * autofs trigger mount mounted on them). But v4 pseudo
> +		 * direct mounts do need the leaves to trigger mounts. In
> +		 * this case we have no choice but to use the list_empty()
> +		 * check and require user space behave.
>  		 */
>  		if (sbi->version > 4) {
> -			if (have_submounts(dentry)) {
> +			if (have_local_submounts(dentry)) {
>  				spin_unlock(&sbi->fs_lock);
>  				goto done;
>  			}
> @@ -431,7 +431,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
>  
>  	/* The daemon never waits. */
>  	if (autofs4_oz_mode(sbi)) {
> -		if (!d_mountpoint(dentry))
> +		if (!is_local_mountpoint(dentry))
>  			return -EISDIR;
>  		return 0;
>  	}
> @@ -460,7 +460,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
>  
>  		if (ino->flags & AUTOFS_INF_WANT_EXPIRE)
>  			return 0;
> -		if (d_mountpoint(dentry))
> +		if (is_local_mountpoint(dentry))
>  			return 0;
>  		inode = d_inode_rcu(dentry);
>  		if (inode && S_ISLNK(inode->i_mode))
> @@ -487,7 +487,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)
>  		 * we can avoid needless calls ->d_automount() and avoid
>  		 * an incorrect ELOOP error return.
>  		 */
> -		if ((!d_mountpoint(dentry) && !simple_empty(dentry)) ||
> +		if ((!is_local_mountpoint(dentry) && !simple_empty(dentry)) ||
>  		    (d_really_is_positive(dentry) && d_is_symlink(dentry)))
>  			status = -EISDIR;
>  	}
> diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
> index 431fd7e..911f4d5 100644
> --- a/fs/autofs4/waitq.c
> +++ b/fs/autofs4/waitq.c
> @@ -333,7 +333,7 @@ static int validate_request(struct autofs_wait_queue **wait,
>  					dentry = new;
>  			}
>  		}
> -		if (have_submounts(dentry))
> +		if (have_local_submounts(dentry))
>  			valid = 0;
>  
>  		if (new)