diff mbox

[6/8] autofs - use path_is_mountpoint() to fix unreliable d_mountpoint() checks

Message ID 20161011053418.27645.15241.stgit@pluto.themaw.net (mailing list archive)
State New, archived
Headers show

Commit Message

Ian Kent Oct. 11, 2016, 5:34 a.m. UTC 
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 in the originating namespace, subsequent
calls to autofs ->d_automount() for that dentry in the original namespace
will return ELOOP until the mount is umounted in the cloned namespace.

Now that a struct path is available where needed use path_is_mountpoint()
instead of d_mountpoint() so we don't get false positives when checking
if a dentry is a mount point in the current namespace.

Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Omar Sandoval <osandov@osandov.com>
---
 fs/autofs4/root.c |   24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)


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Comments

Al Viro Oct. 27, 2016, 2:17 a.m. UTC | #1 
On Tue, Oct 11, 2016 at 01:34:18PM +0800, Ian Kent wrote:
> +	path = file->f_path;
> +
>  	/*
>  	 * An empty directory in an autofs file system is always a
>  	 * mount point. The daemon must have failed to mount this
> @@ -123,7 +126,7 @@ 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 (!path_is_mountpoint(&path) && simple_empty(dentry)) {

Why not &file->f_path, provided that you constify that thing properly?

> +		if (rcu_walk) {
> +			if (!path_is_mountpoint_rcu(path))
> +				return -EISDIR;
> +		} else {
> +			if (!path_is_mountpoint(path))
> +				return -EISDIR;

IDGI.  What's the point of _having_ the _rcu() variant, anyway?  Here you
are probably paying more in terms of i-cache footprint/branch prediction
than you win on not doing that rcu_read_lock()/rcu_read_unlock()...

_rcu variants make sense when non-RCU case does something you can't do
under RCU; here your path_is_mountpoint() is pretty close to being
rcu_read_lock()+path_is_mountpoint_rcu()+rcu_read_unlock() anyway...

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Ian Kent Oct. 27, 2016, 2:51 a.m. UTC | #2 
On Thu, 2016-10-27 at 03:17 +0100, Al Viro wrote:
> On Tue, Oct 11, 2016 at 01:34:18PM +0800, Ian Kent wrote:
> > 
> > +	path = file->f_path;
> > +
> >  	/*
> >  	 * An empty directory in an autofs file system is always a
> >  	 * mount point. The daemon must have failed to mount this
> > @@ -123,7 +126,7 @@ 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 (!path_is_mountpoint(&path) && simple_empty(dentry)) {
> Why not &file->f_path, provided that you constify that thing properly?

Yep, my bad, as pointed out by Eric.

Patches to fix that and constify a bunch of things will follow.

> 
> > 
> > +		if (rcu_walk) {
> > +			if (!path_is_mountpoint_rcu(path))
> > +				return -EISDIR;
> > +		} else {
> > +			if (!path_is_mountpoint(path))
> > +				return -EISDIR;
> IDGI.  What's the point of _having_ the _rcu() variant, anyway?  Here you
> are probably paying more in terms of i-cache footprint/branch prediction
> than you win on not doing that rcu_read_lock()/rcu_read_unlock()...
> 
> _rcu variants make sense when non-RCU case does something you can't do
> under RCU; here your path_is_mountpoint() is pretty close to being
> rcu_read_lock()+path_is_mountpoint_rcu()+rcu_read_unlock() anyway...

Again, my bad, I'll merge these two and post along with the follow up patches
above.

Thanks Al,
Ian
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diff mbox

Patch

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index d47930ad..d7e48fe 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -107,12 +107,15 @@  static int autofs4_dir_open(struct inode *inode, struct file *file)
 {
 	struct dentry *dentry = file->f_path.dentry;
 	struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
+	struct path path;
 
 	pr_debug("file=%p dentry=%p %pd\n", file, dentry, dentry);
 
 	if (autofs4_oz_mode(sbi))
 		goto out;
 
+	path = file->f_path;
+
 	/*
 	 * An empty directory in an autofs file system is always a
 	 * mount point. The daemon must have failed to mount this
@@ -123,7 +126,7 @@  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 (!path_is_mountpoint(&path) && simple_empty(dentry)) {
 		spin_unlock(&sbi->lookup_lock);
 		return -ENOENT;
 	}
@@ -372,15 +375,15 @@  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 path_is_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 (!path_is_mountpoint(path)) {
 		/*
 		 * It's possible that user space hasn't removed directories
 		 * after umounting a rootless multi-mount, although it
@@ -434,8 +437,13 @@  static int autofs4_d_manage(struct path *path, bool rcu_walk)
 
 	/* The daemon never waits. */
 	if (autofs4_oz_mode(sbi)) {
-		if (!d_mountpoint(dentry))
-			return -EISDIR;
+		if (rcu_walk) {
+			if (!path_is_mountpoint_rcu(path))
+				return -EISDIR;
+		} else {
+			if (!path_is_mountpoint(path))
+				return -EISDIR;
+		}
 		return 0;
 	}
 
@@ -463,7 +471,7 @@  static int autofs4_d_manage(struct path *path, bool rcu_walk)
 
 		if (ino->flags & AUTOFS_INF_WANT_EXPIRE)
 			return 0;
-		if (d_mountpoint(dentry))
+		if (path_is_mountpoint_rcu(path))
 			return 0;
 		inode = d_inode_rcu(dentry);
 		if (inode && S_ISLNK(inode->i_mode))
@@ -490,7 +498,7 @@  static int autofs4_d_manage(struct path *path, 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 ((!path_is_mountpoint(path) && !simple_empty(dentry)) ||
 		    (d_really_is_positive(dentry) && d_is_symlink(dentry)))
 			status = -EISDIR;
 	}