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

Ian Kent
2016-10-11T05:34:25Z

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(-)

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;
}