[PATCH v14 09/31] ovl: Modify ovl_lookup() and friends to lookup metacopy dentry

[Vivek Goyal <vgoyal@redhat.com>]

This patch modifies ovl_lookup() and friends to lookup metacopy dentries.
It also allows for presence of metacopy dentries in lower layer.

During lookup, check for presence of OVL_XATTR_METACOPY and if not present,
set OVL_UPPERDATA bit in flags.

We don't support metacopy feature with nfs_export. So in nfs_export code,
we set OVL_UPPERDATA flag set unconditionally if upper inode exists.

Do not follow metacopy origin if we find a metacopy only inode and metacopy
feature is not enabled for that mount. Like redirect, this can have security
implications where an attacker could hand craft upper and try to gain
access to file on lower which it should not have to begin with.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 fs/overlayfs/export.c    |   3 ++
 fs/overlayfs/inode.c     |  11 ++++-
 fs/overlayfs/namei.c     | 102 ++++++++++++++++++++++++++++++++++++++++-------
 fs/overlayfs/overlayfs.h |   1 +
 fs/overlayfs/util.c      |  22 ++++++++++
 5 files changed, 124 insertions(+), 15 deletions(-)

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index 5b7fee1a81ec..e1f6546b6c84 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -311,6 +311,9 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 		return ERR_CAST(inode);
 	}
 
+	if (upper)
+		ovl_set_flag(OVL_UPPERDATA, inode);
+
 	dentry = d_find_any_alias(inode);
 	if (!dentry) {
 		dentry = d_alloc_anon(inode->i_sb);
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 59b1c84076ec..40509b7a50d2 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -776,7 +776,7 @@ struct inode *ovl_get_inode(struct super_block *sb, struct dentry *upperdentry,
 	struct dentry *lowerdentry = lowerpath ? lowerpath->dentry : NULL;
 	bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry, index);
 	int fsid = bylower ? lowerpath->layer->fsid : 0;
-	bool is_dir;
+	bool is_dir, metacopy = false;
 	unsigned long ino = 0;
 	int err = -ENOMEM;
 
@@ -836,6 +836,15 @@ struct inode *ovl_get_inode(struct super_block *sb, struct dentry *upperdentry,
 	if (index)
 		ovl_set_flag(OVL_INDEX, inode);
 
+	if (upperdentry) {
+		err = ovl_check_metacopy_xattr(upperdentry);
+		if (err < 0)
+			goto out_err;
+		metacopy = err;
+		if (!metacopy)
+			ovl_set_flag(OVL_UPPERDATA, inode);
+	}
+
 	OVL_I(inode)->redirect = redirect;
 
 	/* Check for non-merge dir that may have whiteouts */
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index ac81e2c2c976..682f0d402986 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -24,6 +24,7 @@ struct ovl_lookup_data {
 	bool stop;
 	bool last;
 	char *redirect;
+	bool metacopy;
 };
 
 static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
@@ -253,19 +254,29 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
 		goto put_and_out;
 	}
 	if (!d_can_lookup(this)) {
-		d->stop = true;
-		if (d->is_dir)
+		if (d->is_dir) {
+			d->stop = true;
 			goto put_and_out;
-
+		}
 		/*
 		 * NB: handle failure to lookup non-last element when non-dir
 		 * redirects become possible
 		 */
 		WARN_ON(!last_element);
+		err = ovl_check_metacopy_xattr(this);
+		if (err < 0)
+			goto out_err;
+		d->stop = !err;
+		d->metacopy = !!err;
 		goto out;
 	}
-	if (last_element)
+	if (last_element) {
+		if (d->metacopy) {
+			err = -ESTALE;
+			goto out_err;
+		}
 		d->is_dir = true;
+	}
 	if (d->last)
 		goto out;
 
@@ -823,7 +834,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
 	struct ovl_entry *poe = dentry->d_parent->d_fsdata;
 	struct ovl_entry *roe = dentry->d_sb->s_root->d_fsdata;
-	struct ovl_path *stack = NULL;
+	struct ovl_path *stack = NULL, *origin_path = NULL;
 	struct dentry *upperdir, *upperdentry = NULL;
 	struct dentry *origin = NULL;
 	struct dentry *index = NULL;
@@ -834,6 +845,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	struct dentry *this;
 	unsigned int i;
 	int err;
+	bool metacopy = false;
 	struct ovl_lookup_data d = {
 		.name = dentry->d_name,
 		.is_dir = false,
@@ -841,6 +853,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		.stop = false,
 		.last = ofs->config.redirect_follow ? false : !poe->numlower,
 		.redirect = NULL,
+		.metacopy = false,
 	};
 
 	if (dentry->d_name.len > ofs->namelen)
@@ -859,7 +872,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			goto out;
 		}
 		if (upperdentry && !d.is_dir) {
-			BUG_ON(!d.stop || d.redirect);
+			unsigned int origin_ctr = 0;
+			BUG_ON(d.redirect);
 			/*
 			 * Lookup copy up origin by decoding origin file handle.
 			 * We may get a disconnected dentry, which is fine,
@@ -870,9 +884,13 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			 * number - it's the same as if we held a reference
 			 * to a dentry in lower layer that was moved under us.
 			 */
-			err = ovl_check_origin(ofs, upperdentry, &stack, &ctr);
+			err = ovl_check_origin(ofs, upperdentry, &origin_path,
+					       &origin_ctr);
 			if (err)
 				goto out_put_upper;
+
+			if (d.metacopy)
+				metacopy = true;
 		}
 
 		if (d.redirect) {
@@ -913,7 +931,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		 * If no origin fh is stored in upper of a merge dir, store fh
 		 * of lower dir and set upper parent "impure".
 		 */
-		if (upperdentry && !ctr && !ofs->noxattr) {
+		if (upperdentry && !ctr && !ofs->noxattr && d.is_dir) {
 			err = ovl_fix_origin(dentry, this, upperdentry);
 			if (err) {
 				dput(this);
@@ -925,18 +943,36 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		 * When "verify_lower" feature is enabled, do not merge with a
 		 * lower dir that does not match a stored origin xattr. In any
 		 * case, only verified origin is used for index lookup.
+		 *
+		 * For non-dir dentry, make sure dentry found by lookup
+		 * matches the origin stored in upper. Otherwise its an
+		 * error.
 		 */
-		if (upperdentry && !ctr && ovl_verify_lower(dentry->d_sb)) {
+		if (upperdentry && !ctr &&
+		    ((d.is_dir && ovl_verify_lower(dentry->d_sb)) ||
+		     (!d.is_dir && origin_path))) {
 			err = ovl_verify_origin(upperdentry, this, false);
 			if (err) {
 				dput(this);
-				break;
+				if (d.is_dir)
+					break;
+				goto out_put;
 			}
-
-			/* Bless lower dir as verified origin */
+			/* Bless lower as verified origin */
 			origin = this;
 		}
 
+		if (d.metacopy)
+			metacopy = true;
+		/*
+		 * Do not store intermediate metacopy dentries in chain,
+		 * except top most lower metacopy dentry
+		 */
+		if (d.metacopy && ctr) {
+			dput(this);
+			continue;
+		}
+
 		stack[ctr].dentry = this;
 		stack[ctr].layer = lower.layer;
 		ctr++;
@@ -968,13 +1004,43 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		}
 	}
 
+	if (metacopy) {
+		/*
+		 * Found a metacopy dentry but did not find corresponding
+		 * data dentry
+		 */
+		if (d.metacopy) {
+			err = -ESTALE;
+			goto out_put;
+		}
+
+		err = -EPERM;
+		if (!ofs->config.metacopy) {
+			pr_warn_ratelimited("overlay: refusing to follow"
+					    " metacopy origin for (%pd2)\n",
+					    dentry);
+			goto out_put;
+		}
+	} else if (!d.is_dir && upperdentry && !ctr && origin_path) {
+		if (WARN_ON(stack != NULL)) {
+			err = -EIO;
+			goto out_put;
+		}
+		stack = origin_path;
+		ctr = 1;
+		origin_path = NULL;
+	}
+
 	/*
 	 * Lookup index by lower inode and verify it matches upper inode.
 	 * We only trust dir index if we verified that lower dir matches
 	 * origin, otherwise dir index entries may be inconsistent and we
-	 * ignore them. Always lookup index of non-dir and non-upper.
+	 * ignore them.
+	 * For non-dir metacopy dentry, we already set origin if we verified
+	 * that lower matched origin. If not, skip looking up index.
+	 * Always lookup index of non-dir non-metacopy and non-upper.
 	 */
-	if (ctr && (!upperdentry || !d.is_dir))
+	if (ctr && (!upperdentry || (!d.is_dir && !metacopy)))
 		origin = stack[0].dentry;
 
 	if (origin && ovl_indexdir(dentry->d_sb) &&
@@ -1012,6 +1078,10 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	}
 
 	revert_creds(old_cred);
+	if (origin_path) {
+		dput(origin_path->dentry);
+		kfree(origin_path);
+	}
 	dput(index);
 	kfree(stack);
 	kfree(d.redirect);
@@ -1026,6 +1096,10 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		dput(stack[i].dentry);
 	kfree(stack);
 out_put_upper:
+	if (origin_path) {
+		dput(origin_path->dentry);
+		kfree(origin_path);
+	}
 	dput(upperdentry);
 	kfree(upperredirect);
 out:
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index e21156425361..790314079950 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -275,6 +275,7 @@ int ovl_nlink_start(struct dentry *dentry, bool *locked);
 void ovl_nlink_end(struct dentry *dentry, bool locked);
 int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir);
 void ovl_copytimes(struct inode *inode);
+int ovl_check_metacopy_xattr(struct dentry *dentry);
 
 static inline void ovl_copytimes_with_parent(struct dentry *dentry)
 {
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 3b64ecf5cb9b..a32509814f54 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -789,3 +789,25 @@ void ovl_copytimes(struct inode *inode)
 		inode->i_ctime = upperinode->i_ctime;
 	}
 }
+
+/* err < 0, 0 if no metacopy xattr, 1 if metacopy xattr found */
+int ovl_check_metacopy_xattr(struct dentry *dentry)
+{
+	int res;
+
+	/* Only regular files can have metacopy xattr */
+	if (!S_ISREG(d_inode(dentry)->i_mode))
+		return 0;
+
+	res = vfs_getxattr(dentry, OVL_XATTR_METACOPY, NULL, 0);
+	if (res < 0) {
+		if (res == -ENODATA || res == -EOPNOTSUPP)
+			return 0;
+		goto out;
+	}
+
+	return 1;
+out:
+	pr_warn_ratelimited("overlayfs: failed to get metacopy (%i)\n", res);
+	return res;
+}
-- 
2.13.6