Merge branch 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs

Pull overlayfs updates from Miklos Szeredi:
 "This update contains fixes to the "use mounter's permission to access
  underlying layers" area, and miscellaneous other fixes and cleanups.

  No new features this time"

* 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs:
  ovl: use vfs_get_link()
  vfs: add vfs_get_link() helper
  ovl: use generic_readlink
  ovl: explain error values when removing acl from workdir
  ovl: Fix info leak in ovl_lookup_temp()
  ovl: during copy up, switch to mounter's creds early
  ovl: lookup: do getxattr with mounter's permission
  ovl: copy_up_xattr(): use strnlen

fs/namei.c

@@ -4668,6 +4668,31 @@ int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen)
 }
 EXPORT_SYMBOL(generic_readlink);
 
+/**
+ * vfs_get_link - get symlink body
+ * @dentry: dentry on which to get symbolic link
+ * @done: caller needs to free returned data with this
+ *
+ * Calls security hook and i_op->get_link() on the supplied inode.
+ *
+ * It does not touch atime.  That's up to the caller if necessary.
+ *
+ * Does not work on "special" symlinks like /proc/$$/fd/N
+ */
+const char *vfs_get_link(struct dentry *dentry, struct delayed_call *done)
+{
+	const char *res = ERR_PTR(-EINVAL);
+	struct inode *inode = d_inode(dentry);
+
+	if (d_is_symlink(dentry)) {
+		res = ERR_PTR(security_inode_readlink(dentry));
+		if (!res)
+			res = inode->i_op->get_link(dentry, inode, done);
+	}
+	return res;
+}
+EXPORT_SYMBOL(vfs_get_link);
+
 /* get the link contents into pagecache */
 const char *page_get_link(struct dentry *dentry, struct inode *inode,
 			  struct delayed_call *callback)

fs/overlayfs/copy_up.c

@@ -57,6 +57,7 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new)
 	ssize_t list_size, size, value_size = 0;
 	char *buf, *name, *value = NULL;
 	int uninitialized_var(error);
+	size_t slen;
 
 	if (!(old->d_inode->i_opflags & IOP_XATTR) ||
 	    !(new->d_inode->i_opflags & IOP_XATTR))
@@ -79,7 +80,16 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new)
 		goto out;
 	}
 
-	for (name = buf; name < (buf + list_size); name += strlen(name) + 1) {
+	for (name = buf; list_size; name += slen) {
+		slen = strnlen(name, list_size) + 1;
+
+		/* underlying fs providing us with an broken xattr list? */
+		if (WARN_ON(slen > list_size)) {
+			error = -EIO;
+			break;
+		}
+		list_size -= slen;
+
 		if (ovl_is_private_xattr(name))
 			continue;
 retry:
@@ -174,40 +184,6 @@ static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
 	return error;
 }
 
-static char *ovl_read_symlink(struct dentry *realdentry)
-{
-	int res;
-	char *buf;
-	struct inode *inode = realdentry->d_inode;
-	mm_segment_t old_fs;
-
-	res = -EINVAL;
-	if (!inode->i_op->readlink)
-		goto err;
-
-	res = -ENOMEM;
-	buf = (char *) __get_free_page(GFP_KERNEL);
-	if (!buf)
-		goto err;
-
-	old_fs = get_fs();
-	set_fs(get_ds());
-	/* The cast to a user pointer is valid due to the set_fs() */
-	res = inode->i_op->readlink(realdentry,
-				    (char __user *)buf, PAGE_SIZE - 1);
-	set_fs(old_fs);
-	if (res < 0) {
-		free_page((unsigned long) buf);
-		goto err;
-	}
-	buf[res] = '\0';
-
-	return buf;
-
-err:
-	return ERR_PTR(res);
-}
-
 static int ovl_set_timestamps(struct dentry *upperdentry, struct kstat *stat)
 {
 	struct iattr attr = {
@@ -354,19 +330,20 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
 int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 		    struct path *lowerpath, struct kstat *stat)
 {
+	DEFINE_DELAYED_CALL(done);
 	struct dentry *workdir = ovl_workdir(dentry);
 	int err;
 	struct kstat pstat;
 	struct path parentpath;
+	struct dentry *lowerdentry = lowerpath->dentry;
 	struct dentry *upperdir;
 	struct dentry *upperdentry;
-	const struct cred *old_cred;
-	char *link = NULL;
+	const char *link = NULL;
 
 	if (WARN_ON(!workdir))
 		return -EROFS;
 
-	ovl_do_check_copy_up(lowerpath->dentry);
+	ovl_do_check_copy_up(lowerdentry);
 
 	ovl_path_upper(parent, &parentpath);
 	upperdir = parentpath.dentry;
@@ -376,13 +353,11 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 		return err;
 
 	if (S_ISLNK(stat->mode)) {
-		link = ovl_read_symlink(lowerpath->dentry);
+		link = vfs_get_link(lowerdentry, &done);
 		if (IS_ERR(link))
 			return PTR_ERR(link);
 	}
 
-	old_cred = ovl_override_creds(dentry->d_sb);
-
 	err = -EIO;
 	if (lock_rename(workdir, upperdir) != NULL) {
 		pr_err("overlayfs: failed to lock workdir+upperdir\n");
@@ -403,19 +378,16 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 	}
 out_unlock:
 	unlock_rename(workdir, upperdir);
-	revert_creds(old_cred);
-
-	if (link)
-		free_page((unsigned long) link);
+	do_delayed_call(&done);
 
 	return err;
 }
 
 int ovl_copy_up(struct dentry *dentry)
 {
-	int err;
+	int err = 0;
+	const struct cred *old_cred = ovl_override_creds(dentry->d_sb);
 
-	err = 0;
 	while (!err) {
 		struct dentry *next;
 		struct dentry *parent;
@@ -447,6 +419,7 @@ int ovl_copy_up(struct dentry *dentry)
 		dput(parent);
 		dput(next);
 	}
+	revert_creds(old_cred);
 
 	return err;
 }

fs/overlayfs/dir.c

@@ -14,6 +14,7 @@
 #include <linux/cred.h>
 #include <linux/posix_acl.h>
 #include <linux/posix_acl_xattr.h>
+#include <linux/atomic.h>
 #include "overlayfs.h"
 
 void ovl_cleanup(struct inode *wdir, struct dentry *wdentry)
@@ -37,8 +38,10 @@ struct dentry *ovl_lookup_temp(struct dentry *workdir, struct dentry *dentry)
 {
 	struct dentry *temp;
 	char name[20];
+	static atomic_t temp_id = ATOMIC_INIT(0);
 
-	snprintf(name, sizeof(name), "#%lx", (unsigned long) dentry);
+	/* counter is allowed to wrap, since temp dentries are ephemeral */
+	snprintf(name, sizeof(name), "#%x", atomic_inc_return(&temp_id));
 
 	temp = lookup_one_len(name, workdir, strlen(name));
 	if (!IS_ERR(temp) && temp->d_inode) {

fs/overlayfs/inode.c

@@ -19,6 +19,7 @@ static int ovl_copy_up_truncate(struct dentry *dentry)
 	struct dentry *parent;
 	struct kstat stat;
 	struct path lowerpath;
+	const struct cred *old_cred;
 
 	parent = dget_parent(dentry);
 	err = ovl_copy_up(parent);
@@ -26,12 +27,14 @@ static int ovl_copy_up_truncate(struct dentry *dentry)
 		goto out_dput_parent;
 
 	ovl_path_lower(dentry, &lowerpath);
-	err = vfs_getattr(&lowerpath, &stat);
-	if (err)
-		goto out_dput_parent;
 
-	stat.size = 0;
-	err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);
+	old_cred = ovl_override_creds(dentry->d_sb);
+	err = vfs_getattr(&lowerpath, &stat);
+	if (!err) {
+		stat.size = 0;
+		err = ovl_copy_up_one(parent, dentry, &lowerpath, &stat);
+	}
+	revert_creds(old_cred);
 
 out_dput_parent:
 	dput(parent);
@@ -153,45 +156,18 @@ static const char *ovl_get_link(struct dentry *dentry,
 				struct inode *inode,
 				struct delayed_call *done)
 {
-	struct dentry *realdentry;
-	struct inode *realinode;
 	const struct cred *old_cred;
 	const char *p;
 
 	if (!dentry)
 		return ERR_PTR(-ECHILD);
 
-	realdentry = ovl_dentry_real(dentry);
-	realinode = realdentry->d_inode;
-
-	if (WARN_ON(!realinode->i_op->get_link))
-		return ERR_PTR(-EPERM);
-
 	old_cred = ovl_override_creds(dentry->d_sb);
-	p = realinode->i_op->get_link(realdentry, realinode, done);
+	p = vfs_get_link(ovl_dentry_real(dentry), done);
 	revert_creds(old_cred);
 	return p;
 }
 
-static int ovl_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
-{
-	struct path realpath;
-	struct inode *realinode;
-	const struct cred *old_cred;
-	int err;
-
-	ovl_path_real(dentry, &realpath);
-	realinode = realpath.dentry->d_inode;
-
-	if (!realinode->i_op->readlink)
-		return -EINVAL;
-
-	old_cred = ovl_override_creds(dentry->d_sb);
-	err = realinode->i_op->readlink(realpath.dentry, buf, bufsiz);
-	revert_creds(old_cred);
-	return err;
-}
-
 bool ovl_is_private_xattr(const char *name)
 {
 	return strncmp(name, OVL_XATTR_PREFIX,
@@ -375,7 +351,7 @@ static const struct inode_operations ovl_file_inode_operations = {
 static const struct inode_operations ovl_symlink_inode_operations = {
 	.setattr	= ovl_setattr,
 	.get_link	= ovl_get_link,
-	.readlink	= ovl_readlink,
+	.readlink	= generic_readlink,
 	.getattr	= ovl_getattr,
 	.listxattr	= ovl_listxattr,
 	.update_time	= ovl_update_time,

fs/overlayfs/super.c

@@ -273,12 +273,11 @@ static bool ovl_is_opaquedir(struct dentry *dentry)
 {
 	int res;
 	char val;
-	struct inode *inode = dentry->d_inode;
 
-	if (!S_ISDIR(inode->i_mode) || !(inode->i_opflags & IOP_XATTR))
+	if (!d_is_dir(dentry))
 		return false;
 
-	res = __vfs_getxattr(dentry, inode, OVL_XATTR_OPAQUE, &val, 1);
+	res = vfs_getxattr(dentry, OVL_XATTR_OPAQUE, &val, 1);
 	if (res == 1 && val == 'y')
 		return true;
 
@@ -419,16 +418,12 @@ static bool ovl_dentry_weird(struct dentry *dentry)
 				  DCACHE_OP_COMPARE);
 }
 
-static inline struct dentry *ovl_lookup_real(struct super_block *ovl_sb,
-					     struct dentry *dir,
+static inline struct dentry *ovl_lookup_real(struct dentry *dir,
 					     const struct qstr *name)
 {
-	const struct cred *old_cred;
 	struct dentry *dentry;
 
-	old_cred = ovl_override_creds(ovl_sb);
 	dentry = lookup_one_len_unlocked(name->name, dir, name->len);
-	revert_creds(old_cred);
 
 	if (IS_ERR(dentry)) {
 		if (PTR_ERR(dentry) == -ENOENT)
@@ -469,6 +464,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags)
 {
 	struct ovl_entry *oe;
+	const struct cred *old_cred;
 	struct ovl_entry *poe = dentry->d_parent->d_fsdata;
 	struct path *stack = NULL;
 	struct dentry *upperdir, *upperdentry = NULL;
@@ -479,9 +475,10 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	unsigned int i;
 	int err;
 
+	old_cred = ovl_override_creds(dentry->d_sb);
 	upperdir = ovl_upperdentry_dereference(poe);
 	if (upperdir) {
-		this = ovl_lookup_real(dentry->d_sb, upperdir, &dentry->d_name);
+		this = ovl_lookup_real(upperdir, &dentry->d_name);
 		err = PTR_ERR(this);
 		if (IS_ERR(this))
 			goto out;
@@ -514,8 +511,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		bool opaque = false;
 		struct path lowerpath = poe->lowerstack[i];
 
-		this = ovl_lookup_real(dentry->d_sb,
-				       lowerpath.dentry, &dentry->d_name);
+		this = ovl_lookup_real(lowerpath.dentry, &dentry->d_name);
 		err = PTR_ERR(this);
 		if (IS_ERR(this)) {
 			/*
@@ -588,6 +584,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 		ovl_copyattr(realdentry->d_inode, inode);
 	}
 
+	revert_creds(old_cred);
 	oe->opaque = upperopaque;
 	oe->__upperdentry = upperdentry;
 	memcpy(oe->lowerstack, stack, sizeof(struct path) * ctr);
@@ -606,6 +603,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 out_put_upper:
 	dput(upperdentry);
 out:
+	revert_creds(old_cred);
 	return ERR_PTR(err);
 }
 
@@ -834,6 +832,19 @@ static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
 		if (err)
 			goto out_dput;
 
+		/*
+		 * Try to remove POSIX ACL xattrs from workdir.  We are good if:
+		 *
+		 * a) success (there was a POSIX ACL xattr and was removed)
+		 * b) -ENODATA (there was no POSIX ACL xattr)
+		 * c) -EOPNOTSUPP (POSIX ACL xattrs are not supported)
+		 *
+		 * There are various other error values that could effectively
+		 * mean that the xattr doesn't exist (e.g. -ERANGE is returned
+		 * if the xattr name is too long), but the set of filesystems
+		 * allowed as upper are limited to "normal" ones, where checking
+		 * for the above two errors is sufficient.
+		 */
 		err = vfs_removexattr(work, XATTR_NAME_POSIX_ACL_DEFAULT);
 		if (err && err != -ENODATA && err != -EOPNOTSUPP)
 			goto out_dput;

include/linux/fs.h

@@ -2934,6 +2934,7 @@ extern int vfs_stat(const char __user *, struct kstat *);
 extern int vfs_lstat(const char __user *, struct kstat *);
 extern int vfs_fstat(unsigned int, struct kstat *);
 extern int vfs_fstatat(int , const char __user *, struct kstat *, int);
+extern const char *vfs_get_link(struct dentry *, struct delayed_call *);
 
 extern int __generic_block_fiemap(struct inode *inode,
 				  struct fiemap_extent_info *fieinfo,