1 files changed, 152 insertions, 17 deletions

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 5ec4fc2f5d7e..746ea36f3171 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -215,6 +215,9 @@ static void ovl_free_fs(struct ovl_fs *ofs)
 {
 	unsigned i;
 
+	iput(ofs->indexdir_trap);
+	iput(ofs->workdir_trap);
+	iput(ofs->upperdir_trap);
 	dput(ofs->indexdir);
 	dput(ofs->workdir);
 	if (ofs->workdir_locked)
@@ -223,8 +226,10 @@ static void ovl_free_fs(struct ovl_fs *ofs)
 	if (ofs->upperdir_locked)
 		ovl_inuse_unlock(ofs->upper_mnt->mnt_root);
 	mntput(ofs->upper_mnt);
-	for (i = 0; i < ofs->numlower; i++)
+	for (i = 0; i < ofs->numlower; i++) {
+		iput(ofs->lower_layers[i].trap);
 		mntput(ofs->lower_layers[i].mnt);
+	}
 	for (i = 0; i < ofs->numlowerfs; i++)
 		free_anon_bdev(ofs->lower_fs[i].pseudo_dev);
 	kfree(ofs->lower_layers);
@@ -983,7 +988,26 @@ static const struct xattr_handler *ovl_xattr_handlers[] = {
 	NULL
 };
 
-static int ovl_get_upper(struct ovl_fs *ofs, struct path *upperpath)
+static int ovl_setup_trap(struct super_block *sb, struct dentry *dir,
+			  struct inode **ptrap, const char *name)
+{
+	struct inode *trap;
+	int err;
+
+	trap = ovl_get_trap_inode(sb, dir);
+	err = PTR_ERR(trap);
+	if (IS_ERR(trap)) {
+		if (err == -ELOOP)
+			pr_err("overlayfs: conflicting %s path\n", name);
+		return err;
+	}
+
+	*ptrap = trap;
+	return 0;
+}
+
+static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
+			 struct path *upperpath)
 {
 	struct vfsmount *upper_mnt;
 	int err;
@@ -1003,6 +1027,11 @@ static int ovl_get_upper(struct ovl_fs *ofs, struct path *upperpath)
 	if (err)
 		goto out;
 
+	err = ovl_setup_trap(sb, upperpath->dentry, &ofs->upperdir_trap,
+			     "upperdir");
+	if (err)
+		goto out;
+
 	upper_mnt = clone_private_mount(upperpath);
 	err = PTR_ERR(upper_mnt);
 	if (IS_ERR(upper_mnt)) {
@@ -1029,7 +1058,8 @@ out:
 	return err;
 }
 
-static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
+static int ovl_make_workdir(struct super_block *sb, struct ovl_fs *ofs,
+			    struct path *workpath)
 {
 	struct vfsmount *mnt = ofs->upper_mnt;
 	struct dentry *temp;
@@ -1044,6 +1074,10 @@ static int ovl_make_workdir(struct ovl_fs *ofs, struct path *workpath)
 	if (!ofs->workdir)
 		goto out;
 
+	err = ovl_setup_trap(sb, ofs->workdir, &ofs->workdir_trap, "workdir");
+	if (err)
+		goto out;
+
 	/*
 	 * Upper should support d_type, else whiteouts are visible.  Given
 	 * workdir and upper are on same fs, we can do iterate_dir() on
@@ -1104,7 +1138,8 @@ out:
 	return err;
 }
 
-static int ovl_get_workdir(struct ovl_fs *ofs, struct path *upperpath)
+static int ovl_get_workdir(struct super_block *sb, struct ovl_fs *ofs,
+			   struct path *upperpath)
 {
 	int err;
 	struct path workpath = { };
@@ -1135,19 +1170,16 @@ static int ovl_get_workdir(struct ovl_fs *ofs, struct path *upperpath)
 		pr_warn("overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
 	}
 
-	err = ovl_make_workdir(ofs, &workpath);
-	if (err)
-		goto out;
+	err = ovl_make_workdir(sb, ofs, &workpath);
 
-	err = 0;
 out:
 	path_put(&workpath);
 
 	return err;
 }
 
-static int ovl_get_indexdir(struct ovl_fs *ofs, struct ovl_entry *oe,
-			    struct path *upperpath)
+static int ovl_get_indexdir(struct super_block *sb, struct ovl_fs *ofs,
+			    struct ovl_entry *oe, struct path *upperpath)
 {
 	struct vfsmount *mnt = ofs->upper_mnt;
 	int err;
@@ -1166,6 +1198,11 @@ static int ovl_get_indexdir(struct ovl_fs *ofs, struct ovl_entry *oe,
 
 	ofs->indexdir = ovl_workdir_create(ofs, OVL_INDEXDIR_NAME, true);
 	if (ofs->indexdir) {
+		err = ovl_setup_trap(sb, ofs->indexdir, &ofs->indexdir_trap,
+				     "indexdir");
+		if (err)
+			goto out;
+
 		/*
 		 * Verify upper root is exclusively associated with index dir.
 		 * Older kernels stored upper fh in "trusted.overlay.origin"
@@ -1253,8 +1290,8 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
 	return ofs->numlowerfs;
 }
 
-static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
-				unsigned int numlower)
+static int ovl_get_lower_layers(struct super_block *sb, struct ovl_fs *ofs,
+				struct path *stack, unsigned int numlower)
 {
 	int err;
 	unsigned int i;
@@ -1272,16 +1309,28 @@ static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
 
 	for (i = 0; i < numlower; i++) {
 		struct vfsmount *mnt;
+		struct inode *trap;
 		int fsid;
 
 		err = fsid = ovl_get_fsid(ofs, &stack[i]);
 		if (err < 0)
 			goto out;
 
+		err = -EBUSY;
+		if (ovl_is_inuse(stack[i].dentry)) {
+			pr_err("overlayfs: lowerdir is in-use as upperdir/workdir\n");
+			goto out;
+		}
+
+		err = ovl_setup_trap(sb, stack[i].dentry, &trap, "lowerdir");
+		if (err)
+			goto out;
+
 		mnt = clone_private_mount(&stack[i]);
 		err = PTR_ERR(mnt);
 		if (IS_ERR(mnt)) {
 			pr_err("overlayfs: failed to clone lowerpath\n");
+			iput(trap);
 			goto out;
 		}
 
@@ -1291,6 +1340,7 @@ static int ovl_get_lower_layers(struct ovl_fs *ofs, struct path *stack,
 		 */
 		mnt->mnt_flags |= MNT_READONLY | MNT_NOATIME;
 
+		ofs->lower_layers[ofs->numlower].trap = trap;
 		ofs->lower_layers[ofs->numlower].mnt = mnt;
 		ofs->lower_layers[ofs->numlower].idx = i + 1;
 		ofs->lower_layers[ofs->numlower].fsid = fsid;
@@ -1385,7 +1435,7 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
 		goto out_err;
 	}
 
-	err = ovl_get_lower_layers(ofs, stack, numlower);
+	err = ovl_get_lower_layers(sb, ofs, stack, numlower);
 	if (err)
 		goto out_err;
 
@@ -1417,6 +1467,85 @@ out_err:
 	goto out;
 }
 
+/*
+ * Check if this layer root is a descendant of:
+ * - another layer of this overlayfs instance
+ * - upper/work dir of any overlayfs instance
+ * - a disconnected dentry (detached root)
+ */
+static int ovl_check_layer(struct super_block *sb, struct dentry *dentry,
+			   const char *name)
+{
+	struct dentry *next, *parent;
+	bool is_root = false;
+	int err = 0;
+
+	if (!dentry || dentry == dentry->d_sb->s_root)
+		return 0;
+
+	next = dget(dentry);
+	/* Walk back ancestors to fs root (inclusive) looking for traps */
+	do {
+		parent = dget_parent(next);
+		is_root = (parent == next);
+		if (ovl_is_inuse(parent)) {
+			err = -EBUSY;
+			pr_err("overlayfs: %s path overlapping in-use upperdir/workdir\n",
+			       name);
+		} else if (ovl_lookup_trap_inode(sb, parent)) {
+			err = -ELOOP;
+			pr_err("overlayfs: overlapping %s path\n", name);
+		}
+		dput(next);
+		next = parent;
+	} while (!err && !is_root);
+
+	/* Did we really walk to fs root or found a detached root? */
+	if (!err && next != dentry->d_sb->s_root) {
+		err = -ESTALE;
+		pr_err("overlayfs: disconnected %s path\n", name);
+	}
+
+	dput(next);
+
+	return err;
+}
+
+/*
+ * Check if any of the layers or work dirs overlap.
+ */
+static int ovl_check_overlapping_layers(struct super_block *sb,
+					struct ovl_fs *ofs)
+{
+	int i, err;
+
+	if (ofs->upper_mnt) {
+		err = ovl_check_layer(sb, ofs->upper_mnt->mnt_root, "upperdir");
+		if (err)
+			return err;
+
+		/*
+		 * Checking workbasedir avoids hitting ovl_is_inuse(parent) of
+		 * this instance and covers overlapping work and index dirs,
+		 * unless work or index dir have been moved since created inside
+		 * workbasedir.  In that case, we already have their traps in
+		 * inode cache and we will catch that case on lookup.
+		 */
+		err = ovl_check_layer(sb, ofs->workbasedir, "workdir");
+		if (err)
+			return err;
+	}
+
+	for (i = 0; i < ofs->numlower; i++) {
+		err = ovl_check_layer(sb, ofs->lower_layers[i].mnt->mnt_root,
+				      "lowerdir");
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
 static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 {
 	struct path upperpath = { };
@@ -1456,17 +1585,20 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	if (ofs->config.xino != OVL_XINO_OFF)
 		ofs->xino_bits = BITS_PER_LONG - 32;
 
+	/* alloc/destroy_inode needed for setting up traps in inode cache */
+	sb->s_op = &ovl_super_operations;
+
 	if (ofs->config.upperdir) {
 		if (!ofs->config.workdir) {
 			pr_err("overlayfs: missing 'workdir'\n");
 			goto out_err;
 		}
 
-		err = ovl_get_upper(ofs, &upperpath);
+		err = ovl_get_upper(sb, ofs, &upperpath);
 		if (err)
 			goto out_err;
 
-		err = ovl_get_workdir(ofs, &upperpath);
+		err = ovl_get_workdir(sb, ofs, &upperpath);
 		if (err)
 			goto out_err;
 
@@ -1487,7 +1619,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 		sb->s_flags |= SB_RDONLY;
 
 	if (!(ovl_force_readonly(ofs)) && ofs->config.index) {
-		err = ovl_get_indexdir(ofs, oe, &upperpath);
+		err = ovl_get_indexdir(sb, ofs, oe, &upperpath);
 		if (err)
 			goto out_free_oe;
 
@@ -1500,6 +1632,10 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 	}
 
+	err = ovl_check_overlapping_layers(sb, ofs);
+	if (err)
+		goto out_free_oe;
+
 	/* Show index=off in /proc/mounts for forced r/o mount */
 	if (!ofs->indexdir) {
 		ofs->config.index = false;
@@ -1521,7 +1657,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
 
 	sb->s_magic = OVERLAYFS_SUPER_MAGIC;
-	sb->s_op = &ovl_super_operations;
 	sb->s_xattr = ovl_xattr_handlers;
 	sb->s_fs_info = ofs;
 	sb->s_flags |= SB_POSIXACL;