}
/*
- * serialization is taken care of in namespace.c
+ * Perform an automount
+ * - return -EISDIR to tell follow_managed() to stop and return the path we
+ * were called with.
*/
-static void __follow_mount_rcu(struct nameidata *nd, struct path *path,
- struct inode **inode)
+static int follow_automount(struct path *path, unsigned flags,
+ bool *need_mntput)
{
- while (d_mountpoint(path->dentry)) {
- struct vfsmount *mounted;
- mounted = __lookup_mnt(path->mnt, path->dentry, 1);
- if (!mounted)
- return;
- path->mnt = mounted;
- path->dentry = mounted->mnt_root;
- nd->seq = read_seqcount_begin(&path->dentry->d_seq);
- *inode = path->dentry->d_inode;
+ struct vfsmount *mnt;
+
+ if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
+ return -EREMOTE;
+
+ /* We want to mount if someone is trying to open/create a file of any
+ * type under the mountpoint, wants to traverse through the mountpoint
+ * or wants to open the mounted directory.
+ *
+ * We don't want to mount if someone's just doing a stat and they've
+ * set AT_SYMLINK_NOFOLLOW - unless they're stat'ing a directory and
+ * appended a '/' to the name.
+ */
+ if (!(flags & LOOKUP_FOLLOW) &&
+ !(flags & (LOOKUP_CONTINUE | LOOKUP_DIRECTORY |
+ LOOKUP_OPEN | LOOKUP_CREATE)))
+ return -EISDIR;
+
+ current->total_link_count++;
+ if (current->total_link_count >= 40)
+ return -ELOOP;
+
+ mnt = path->dentry->d_op->d_automount(path);
+ if (IS_ERR(mnt)) {
+ /*
+ * The filesystem is allowed to return -EISDIR here to indicate
+ * it doesn't want to automount. For instance, autofs would do
+ * this so that its userspace daemon can mount on this dentry.
+ *
+ * However, we can only permit this if it's a terminal point in
+ * the path being looked up; if it wasn't then the remainder of
+ * the path is inaccessible and we should say so.
+ */
+ if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_CONTINUE))
+ return -EREMOTE;
+ return PTR_ERR(mnt);
}
-}
+ if (!mnt) /* mount collision */
+ return 0;
-static int __follow_mount(struct path *path)
-{
- int res = 0;
- while (d_mountpoint(path->dentry)) {
- struct vfsmount *mounted = lookup_mnt(path);
- if (!mounted)
- break;
- dput(path->dentry);
- if (res)
- mntput(path->mnt);
- path->mnt = mounted;
- path->dentry = dget(mounted->mnt_root);
- res = 1;
+ if (mnt->mnt_sb == path->mnt->mnt_sb &&
+ mnt->mnt_root == path->dentry) {
+ mntput(mnt);
+ return -ELOOP;
}
- return res;
+
+ dput(path->dentry);
+ if (*need_mntput)
+ mntput(path->mnt);
+ path->mnt = mnt;
+ path->dentry = dget(mnt->mnt_root);
+ *need_mntput = true;
+ return 0;
}
-static void follow_mount(struct path *path)
+/*
+ * Handle a dentry that is managed in some way.
+ * - Flagged as mountpoint
+ * - Flagged as automount point
+ *
+ * This may only be called in refwalk mode.
+ *
+ * Serialization is taken care of in namespace.c
+ */
+static int follow_managed(struct path *path, unsigned flags)
{
- while (d_mountpoint(path->dentry)) {
- struct vfsmount *mounted = lookup_mnt(path);
- if (!mounted)
- break;
- dput(path->dentry);
- mntput(path->mnt);
- path->mnt = mounted;
- path->dentry = dget(mounted->mnt_root);
+ unsigned managed;
+ bool need_mntput = false;
+ int ret;
+
+ /* Given that we're not holding a lock here, we retain the value in a
+ * local variable for each dentry as we look at it so that we don't see
+ * the components of that value change under us */
+ while (managed = ACCESS_ONCE(path->dentry->d_flags),
+ managed &= DCACHE_MANAGED_DENTRY,
+ unlikely(managed != 0)) {
+ /* Transit to a mounted filesystem. */
+ if (managed & DCACHE_MOUNTED) {
+ struct vfsmount *mounted = lookup_mnt(path);
+ if (mounted) {
+ dput(path->dentry);
+ if (need_mntput)
+ mntput(path->mnt);
+ path->mnt = mounted;
+ path->dentry = dget(mounted->mnt_root);
+ need_mntput = true;
+ continue;
+ }
+
+ /* Something is mounted on this dentry in another
+ * namespace and/or whatever was mounted there in this
+ * namespace got unmounted before we managed to get the
+ * vfsmount_lock */
+ }
+
+ /* Handle an automount point */
+ if (managed & DCACHE_NEED_AUTOMOUNT) {
+ ret = follow_automount(path, flags, &need_mntput);
+ if (ret < 0)
+ return ret == -EISDIR ? 0 : ret;
+ continue;
+ }
+
+ /* We didn't change the current path point */
+ break;
}
+ return 0;
}
int follow_down(struct path *path)
return 0;
}
+/*
+ * Skip to top of mountpoint pile in rcuwalk mode. We abort the rcu-walk if we
+ * meet an automount point and we're not walking to "..". True is returned to
+ * continue, false to abort.
+ */
+static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
+ struct inode **inode, bool reverse_transit)
+{
+ while (d_mountpoint(path->dentry)) {
+ struct vfsmount *mounted;
+ mounted = __lookup_mnt(path->mnt, path->dentry, 1);
+ if (!mounted)
+ break;
+ path->mnt = mounted;
+ path->dentry = mounted->mnt_root;
+ nd->seq = read_seqcount_begin(&path->dentry->d_seq);
+ *inode = path->dentry->d_inode;
+ }
+
+ if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
+ return reverse_transit;
+ return true;
+}
+
static int follow_dotdot_rcu(struct nameidata *nd)
{
struct inode *inode = nd->inode;
set_root_rcu(nd);
- while(1) {
+ while (1) {
if (nd->path.dentry == nd->root.dentry &&
nd->path.mnt == nd->root.mnt) {
break;
nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq);
inode = nd->path.dentry->d_inode;
}
- __follow_mount_rcu(nd, &nd->path, &inode);
+ __follow_mount_rcu(nd, &nd->path, &inode, true);
nd->inode = inode;
return 0;
}
+/*
+ * Skip to top of mountpoint pile in refwalk mode for follow_dotdot()
+ */
+static void follow_mount(struct path *path)
+{
+ while (d_mountpoint(path->dentry)) {
+ struct vfsmount *mounted = lookup_mnt(path);
+ if (!mounted)
+ break;
+ dput(path->dentry);
+ mntput(path->mnt);
+ path->mnt = mounted;
+ path->dentry = dget(mounted->mnt_root);
+ }
+}
+
static void follow_dotdot(struct nameidata *nd)
{
set_root(nd);
struct vfsmount *mnt = nd->path.mnt;
struct dentry *dentry, *parent = nd->path.dentry;
struct inode *dir;
+ int err;
+
/*
* See if the low-level filesystem might want
* to use its own hash..
*/
if (unlikely(parent->d_flags & DCACHE_OP_HASH)) {
- int err = parent->d_op->d_hash(parent, nd->inode, name);
+ err = parent->d_op->d_hash(parent, nd->inode, name);
if (err < 0)
return err;
}
done2:
path->mnt = mnt;
path->dentry = dentry;
- __follow_mount_rcu(nd, path, inode);
- } else {
- dentry = __d_lookup(parent, name);
- if (!dentry)
- goto need_lookup;
+ if (likely(__follow_mount_rcu(nd, path, inode, false)))
+ return 0;
+ if (nameidata_drop_rcu(nd))
+ return -ECHILD;
+ /* fallthru */
+ }
+ dentry = __d_lookup(parent, name);
+ if (!dentry)
+ goto need_lookup;
found:
- if (dentry->d_flags & DCACHE_OP_REVALIDATE)
- goto need_revalidate;
+ if (dentry->d_flags & DCACHE_OP_REVALIDATE)
+ goto need_revalidate;
done:
- path->mnt = mnt;
- path->dentry = dentry;
- __follow_mount(path);
- *inode = path->dentry->d_inode;
- }
+ path->mnt = mnt;
+ path->dentry = dentry;
+ err = follow_managed(path, nd->flags);
+ if (unlikely(err < 0))
+ return err;
+ *inode = path->dentry->d_inode;
return 0;
need_lookup:
if (open_flag & O_EXCL)
goto exit_dput;
- if (__follow_mount(path)) {
- error = -ELOOP;
- if (open_flag & O_NOFOLLOW)
- goto exit_dput;
- }
+ error = follow_managed(path, nd->flags);
+ if (error < 0)
+ goto exit_dput;
error = -ENOENT;
if (!path->dentry->d_inode)
projects / GitHub / LineageOS / android_kernel_motorola_exynos9610.git / commitdiff