1 files changed, 280 insertions, 99 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 8df7a78ace58..8f7b41a14882 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -368,18 +368,6 @@ void path_get(struct path *path)
 EXPORT_SYMBOL(path_get);
 
 /**
- * path_get_long - get a long reference to a path
- * @path: path to get the reference to
- *
- * Given a path increment the reference count to the dentry and the vfsmount.
- */
-void path_get_long(struct path *path)
-{
-        mntget_long(path->mnt);
-        dget(path->dentry);
-}
-
-/**
  * path_put - put a reference to a path
  * @path: path to put the reference to
  *
@@ -393,18 +381,6 @@ void path_put(struct path *path)
 EXPORT_SYMBOL(path_put);
 
 /**
- * path_put_long - put a long reference to a path
- * @path: path to put the reference to
- *
- * Given a path decrement the reference count to the dentry and the vfsmount.
- */
-void path_put_long(struct path *path)
-{
-        dput(path->dentry);
-        mntput_long(path->mnt);
-}
-
-/**
  * nameidata_drop_rcu - drop this nameidata out of rcu-walk
  * @nd: nameidata pathwalk data to drop
  * Returns: 0 on success, -ECHILD on failure
@@ -800,12 +776,8 @@ __do_follow_link(const struct path *link, struct nameidata *nd, void **p)
         touch_atime(link->mnt, dentry);
         nd_set_link(nd, NULL);
 
-        if (link->mnt != nd->path.mnt) {
-                path_to_nameidata(link, nd);
-                nd->inode = nd->path.dentry->d_inode;
-                dget(dentry);
-        }
-        mntget(link->mnt);
+        if (link->mnt == nd->path.mnt)
+                mntget(link->mnt);
 
         nd->last_type = LAST_BIND;
         *p = dentry->d_inode->i_op->follow_link(dentry, nd);
@@ -896,54 +868,169 @@ int follow_up(struct path *path)
 }
 
 /*
- * 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;
+        int err;
+
+        if (!path->dentry->d_op || !path->dentry->d_op->d_automount)
+                return -EREMOTE;
+
+        /* We don't want to mount if someone supplied AT_NO_AUTOMOUNT
+         * and this is the terminal part of the path.
+         */
+        if ((flags & LOOKUP_NO_AUTOMOUNT) && !(flags & LOOKUP_CONTINUE))
+                return -EISDIR; /* we actually want to stop here */
+
+        /* 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);
         }
-}
 
-static int __follow_mount(struct path *path)
-{
-        int res = 0;
-        while (d_mountpoint(path->dentry)) {
-                struct vfsmount *mounted = lookup_mnt(path);
-                if (!mounted)
-                        break;
+        if (!mnt) /* mount collision */
+                return 0;
+
+        /* The new mount record should have at least 2 refs to prevent it being
+         * expired before we get a chance to add it
+         */
+        BUG_ON(mnt_get_count(mnt) < 2);
+
+        if (mnt->mnt_sb == path->mnt->mnt_sb &&
+            mnt->mnt_root == path->dentry) {
+                mnt_clear_expiry(mnt);
+                mntput(mnt);
+                mntput(mnt);
+                return -ELOOP;
+        }
+
+        /* We need to add the mountpoint to the parent.  The filesystem may
+         * have placed it on an expiry list, and so we need to make sure it
+         * won't be expired under us if do_add_mount() fails (do_add_mount()
+         * will eat a reference unconditionally).
+         */
+        mntget(mnt);
+        err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE);
+        switch (err) {
+        case -EBUSY:
+                /* Someone else made a mount here whilst we were busy */
+                err = 0;
+        default:
+                mnt_clear_expiry(mnt);
+                mntput(mnt);
+                mntput(mnt);
+                return err;
+        case 0:
+                mntput(mnt);
                 dput(path->dentry);
-                if (res)
+                if (*need_mntput)
                         mntput(path->mnt);
-                path->mnt = mounted;
-                path->dentry = dget(mounted->mnt_root);
-                res = 1;
+                path->mnt = mnt;
+                path->dentry = dget(mnt->mnt_root);
+                *need_mntput = true;
+                return 0;
         }
-        return res;
 }
 
-static void follow_mount(struct path *path)
+/*
+ * Handle a dentry that is managed in some way.
+ * - Flagged for transit management (autofs)
+ * - 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)) {
+                /* Allow the filesystem to manage the transit without i_mutex
+                 * being held. */
+                if (managed & DCACHE_MANAGE_TRANSIT) {
+                        BUG_ON(!path->dentry->d_op);
+                        BUG_ON(!path->dentry->d_op->d_manage);
+                        ret = path->dentry->d_op->d_manage(path->dentry,
+                                                           false, false);
+                        if (ret < 0)
+                                return ret == -EISDIR ? 0 : ret;
+                }
+
+                /* 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)
+int follow_down_one(struct path *path)
 {
         struct vfsmount *mounted;
 
@@ -958,13 +1045,41 @@ 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 a managed dentry 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;
+                if (unlikely(path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) &&
+                    !reverse_transit &&
+                    path->dentry->d_op->d_manage(path->dentry, false, true) < 0)
+                        return false;
+                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;
@@ -987,12 +1102,80 @@ static int follow_dotdot_rcu(struct nameidata *nd)
                 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;
 }
 
+/*
+ * Follow down to the covering mount currently visible to userspace.  At each
+ * point, the filesystem owning that dentry may be queried as to whether the
+ * caller is permitted to proceed or not.
+ *
+ * Care must be taken as namespace_sem may be held (indicated by mounting_here
+ * being true).
+ */
+int follow_down(struct path *path, bool mounting_here)
+{
+        unsigned managed;
+        int ret;
+
+        while (managed = ACCESS_ONCE(path->dentry->d_flags),
+               unlikely(managed & DCACHE_MANAGED_DENTRY)) {
+                /* Allow the filesystem to manage the transit without i_mutex
+                 * being held.
+                 *
+                 * We indicate to the filesystem if someone is trying to mount
+                 * something here.  This gives autofs the chance to deny anyone
+                 * other than its daemon the right to mount on its
+                 * superstructure.
+                 *
+                 * The filesystem may sleep at this point.
+                 */
+                if (managed & DCACHE_MANAGE_TRANSIT) {
+                        BUG_ON(!path->dentry->d_op);
+                        BUG_ON(!path->dentry->d_op->d_manage);
+                        ret = path->dentry->d_op->d_manage(
+                                path->dentry, mounting_here, false);
+                        if (ret < 0)
+                                return ret == -EISDIR ? 0 : ret;
+                }
+
+                /* Transit to a mounted filesystem. */
+                if (managed & DCACHE_MOUNTED) {
+                        struct vfsmount *mounted = lookup_mnt(path);
+                        if (!mounted)
+                                break;
+                        dput(path->dentry);
+                        mntput(path->mnt);
+                        path->mnt = mounted;
+                        path->dentry = dget(mounted->mnt_root);
+                        continue;
+                }
+
+                /* Don't handle automount points here */
+                break;
+        }
+        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);
@@ -1057,12 +1240,14 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
         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;
         }
@@ -1089,22 +1274,28 @@ static int do_lookup(struct nameidata *nd, struct qstr *name,
                 nd->seq = seq;
                 if (dentry->d_flags & DCACHE_OP_REVALIDATE)
                         goto need_revalidate;
+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:
@@ -1143,6 +1334,8 @@ need_revalidate:
                 goto need_lookup;
         if (IS_ERR(dentry))
                 goto fail;
+        if (nd->flags & LOOKUP_RCU)
+                goto done2;
         goto done;
 
 fail:
@@ -1150,17 +1343,6 @@ fail:
 }
 
 /*
- * This is a temporary kludge to deal with "automount" symlinks; proper
- * solution is to trigger them on follow_mount(), so that do_lookup()
- * would DTRT.  To be killed before 2.6.34-final.
- */
-static inline int follow_on_final(struct inode *inode, unsigned lookup_flags)
-{
-        return inode && unlikely(inode->i_op->follow_link) &&
-                ((lookup_flags & LOOKUP_FOLLOW) || S_ISDIR(inode->i_mode));
-}
-
-/*
  * Name resolution.
  * This is the basic name resolution function, turning a pathname into
  * the final dentry. We expect 'base' to be positive and a directory.
@@ -1298,7 +1480,8 @@ last_component:
                 err = do_lookup(nd, &this, &next, &inode);
                 if (err)
                         break;
-                if (follow_on_final(inode, lookup_flags)) {
+                if (inode && unlikely(inode->i_op->follow_link) &&
+                    (lookup_flags & LOOKUP_FOLLOW)) {
                         if (nameidata_dentry_drop_rcu_maybe(nd, next.dentry))
                                 return -ECHILD;
                         BUG_ON(inode != next.dentry->d_inode);
@@ -2200,11 +2383,9 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
         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)
@@ -2353,8 +2534,7 @@ reval:
                 struct inode *linki = link.dentry->d_inode;
                 void *cookie;
                 error = -ELOOP;
-                /* S_ISDIR part is a temporary automount kludge */
-                if (!(nd.flags & LOOKUP_FOLLOW) && !S_ISDIR(linki->i_mode))
+                if (!(nd.flags & LOOKUP_FOLLOW))
                         goto exit_dput;
                 if (count++ == 32)
                         goto exit_dput;
@@ -3413,6 +3593,7 @@ const struct inode_operations page_symlink_inode_operations = {
 };
 
 EXPORT_SYMBOL(user_path_at);
+EXPORT_SYMBOL(follow_down_one);
 EXPORT_SYMBOL(follow_down);
 EXPORT_SYMBOL(follow_up);
 EXPORT_SYMBOL(get_write_access); /* binfmt_aout */