Re: Autofs and mount namespaces

[Ian Kent <raven@themaw.net>]

On Tue, 2016-07-05 at 11:47 -0700, Omar Sandoval wrote:
> On Fri, Apr 08, 2016 at 08:51:03AM +0800, Ian Kent wrote:
> [snip]
> > 
> > I think this is a better approach (beware, not even compile tested so it
> > almost certainly doesn't work properly) and I'm not even sure that
> > exposing __is_local_mountpoint() is ok from a VFS POV but something
> > needs to be done:
> > 
> > autofs4 - make mountpoint checks namespace aware
> > 
> > From: Ian Kent <ikent@redhat.com>
> > 
> > If an automount mount is clone(2)ed into a file system that is
> > propagation private, when it later expires the mount subsequent
> > calls to autofs ->d_automount() for in that dentry in that
> > namespace will return ELOOP until the mount is manually umounted.
> > 
> > In the same way, if an autofs mount is triggered by automount(8)
> > 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.
> > 
> > Signed-off-by: Ian Kent <ikent@redhat.com>
> > Cc: Al Viro <viro@ZenIV.linux.org.uk>
> > Cc: Eric W. Biederman <ebiederm@xmission.com>
> > ---
> >  fs/autofs4/expire.c   |    4 ++--
> >  fs/autofs4/root.c     |   14 +++++++-------
> >  fs/dcache.c           |    2 +-
> >  fs/mount.h            |    9 ---------
> >  fs/namespace.c        |    1 +
> >  include/linux/mount.h |    9 +++++++++
> >  6 files changed, 20 insertions(+), 19 deletions(-)
> > 
> > diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
> > index 9510d8d..23b9701 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 7ab9239..9ba487a 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;
> >  	}
> > @@ -370,15 +370,15 @@ 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
> > @@ -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_EXPIRING | AUTOFS_INF_NO_RCU))
> >  			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/dcache.c b/fs/dcache.c
> > index 32ceae3..9c42dc9 100644
> > --- a/fs/dcache.c
> > +++ b/fs/dcache.c
> > @@ -1271,7 +1271,7 @@ rename_retry:
> >  static enum d_walk_ret check_mount(void *data, struct dentry *dentry)
> >  {
> >  	int *ret = data;
> > -	if (d_mountpoint(dentry)) {
> > +	if (is_local_mountpoint(dentry)) {
> >  		*ret = 1;
> >  		return D_WALK_QUIT;
> >  	}
> > diff --git a/fs/mount.h b/fs/mount.h
> > index 14db05d..c25e6e8 100644
> > --- a/fs/mount.h
> > +++ b/fs/mount.h
> > @@ -127,12 +127,3 @@ struct proc_mounts {
> >  };
> >  
> >  extern const struct seq_operations mounts_op;
> > -
> > -extern bool __is_local_mountpoint(struct dentry *dentry);
> > -static inline bool is_local_mountpoint(struct dentry *dentry)
> > -{
> > -	if (!d_mountpoint(dentry))
> > -		return false;
> > -
> > -	return __is_local_mountpoint(dentry);
> > -}
> > diff --git a/fs/namespace.c b/fs/namespace.c
> > index 4fb1691..9e1bc00 100644
> > --- a/fs/namespace.c
> > +++ b/fs/namespace.c
> > @@ -725,6 +725,7 @@ bool __is_local_mountpoint(struct dentry *dentry)
> >  out:
> >  	return is_covered;
> >  }
> > +EXPORT_SYMBOL(__is_local_mountpoint);
> >  
> >  static struct mountpoint *lookup_mountpoint(struct dentry *dentry)
> >  {
> > diff --git a/include/linux/mount.h b/include/linux/mount.h
> > index f822c3c..7419c0c 100644
> > --- a/include/linux/mount.h
> > +++ b/include/linux/mount.h
> > @@ -15,6 +15,7 @@
> >  #include <linux/spinlock.h>
> >  #include <linux/seqlock.h>
> >  #include <linux/atomic.h>
> > +#include <linux/dcache.h>
> >  
> >  struct super_block;
> >  struct vfsmount;
> > @@ -95,4 +96,12 @@ extern void mark_mounts_for_expiry(struct list_head
> > *mounts);
> >  
> >  extern dev_t name_to_dev_t(const char *name);
> >  
> > +extern bool __is_local_mountpoint(struct dentry *dentry);
> > +static inline bool is_local_mountpoint(struct dentry *dentry)
> > +{
> > +	if (!d_mountpoint(dentry))
> > +		return false;
> > +
> > +	return __is_local_mountpoint(dentry);
> > +}
> >  #endif /* _LINUX_MOUNT_H */
> 
> Hi, Ian,
> 
> Just wanted to check on the status of this fix. Is this still the
> approach you wanted to take/is there anything else you wanted to do with
> this?

The problem is that someone tested this back ported to an older kernel and
claimed it caused file system corruption.

That leaves me in a bad place indeed.

Ian