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Commit 227701e0 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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

Pull overlayfs fixes from Miklos Szeredi:

 - fix incomplete syncing of filesystem

 - fix regression in readdir on ovl over 9p

 - only follow redirects when needed

 - misc fixes and cleanups

* 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs:
  ovl: fix overlay: warning prefix
  ovl: Use PTR_ERR_OR_ZERO()
  ovl: Sync upper dirty data when syncing overlayfs
  ovl: update ctx->pos on impure dir iteration
  ovl: Pass ovl_get_nlink() parameters in right order
  ovl: don't follow redirects if redirect_dir=off
parents 06f976ec da2e6b7e

Documentation/filesystems/overlayfs.txt

+34 −0
Original line number Diff line number Diff line
@@ -156,6 +156,40 @@ handle it in two different ways: 
   root of the overlay.  Finally the directory is moved to the new

   location.



There are several ways to tune the "redirect_dir" feature.



Kernel config options:



- OVERLAY_FS_REDIRECT_DIR:

    If this is enabled, then redirect_dir is turned on by  default.

- OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW:

    If this is enabled, then redirects are always followed by default. Enabling

    this results in a less secure configuration.  Enable this option only when

    worried about backward compatibility with kernels that have the redirect_dir

    feature and follow redirects even if turned off.



Module options (can also be changed through /sys/module/overlay/parameters/*):



- "redirect_dir=BOOL":

    See OVERLAY_FS_REDIRECT_DIR kernel config option above.

- "redirect_always_follow=BOOL":

    See OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW kernel config option above.

- "redirect_max=NUM":

    The maximum number of bytes in an absolute redirect (default is 256).



Mount options:



- "redirect_dir=on":

    Redirects are enabled.

- "redirect_dir=follow":

    Redirects are not created, but followed.

- "redirect_dir=off":

    Redirects are not created and only followed if "redirect_always_follow"

    feature is enabled in the kernel/module config.

- "redirect_dir=nofollow":

    Redirects are not created and not followed (equivalent to "redirect_dir=off"

    if "redirect_always_follow" feature is not enabled).



Non-directories

---------------

fs/overlayfs/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -24,6 +24,16 @@ config OVERLAY_FS_REDIRECT_DIR 
	  an overlay which has redirects on a kernel that doesn't support this

	  feature will have unexpected results.



config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW

	bool "Overlayfs: follow redirects even if redirects are turned off"

	default y

	depends on OVERLAY_FS

	help

	  Disable this to get a possibly more secure configuration, but that

	  might not be backward compatible with previous kernels.



	  For more information, see Documentation/filesystems/overlayfs.txt



config OVERLAY_FS_INDEX

	bool "Overlayfs: turn on inodes index feature by default"

	depends on OVERLAY_FS

fs/overlayfs/dir.c

+2 −1
Original line number Diff line number Diff line
@@ -887,7 +887,8 @@ static int ovl_set_redirect(struct dentry *dentry, bool samedir) 
		spin_unlock(&dentry->d_lock);

	} else {

		kfree(redirect);

		pr_warn_ratelimited("overlay: failed to set redirect (%i)\n", err);

		pr_warn_ratelimited("overlayfs: failed to set redirect (%i)\n",

				    err);

		/* Fall back to userspace copy-up */

		err = -EXDEV;

	}

fs/overlayfs/namei.c

+17 −1
Original line number Diff line number Diff line
@@ -435,7 +435,7 @@ int ovl_verify_index(struct dentry *index, struct ovl_path *lower, 


	/* Check if index is orphan and don't warn before cleaning it */

	if (d_inode(index)->i_nlink == 1 &&

	    ovl_get_nlink(index, origin.dentry, 0) == 0)

	    ovl_get_nlink(origin.dentry, index, 0) == 0)

		err = -ENOENT;



	dput(origin.dentry);
@@ -681,6 +681,22 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry, 
		if (d.stop)

			break;



		/*

		 * Following redirects can have security consequences: it's like

		 * a symlink into the lower layer without the permission checks.

		 * This is only a problem if the upper layer is untrusted (e.g

		 * comes from an USB drive).  This can allow a non-readable file

		 * or directory to become readable.

		 *

		 * Only following redirects when redirects are enabled disables

		 * this attack vector when not necessary.

		 */

		err = -EPERM;

		if (d.redirect && !ofs->config.redirect_follow) {

			pr_warn_ratelimited("overlay: refusing to follow redirect for (%pd2)\n", dentry);

			goto out_put;

		}



		if (d.redirect && d.redirect[0] == '/' && poe != roe) {

			poe = roe;

fs/overlayfs/overlayfs.h

+1 −1
Original line number Diff line number Diff line
@@ -180,7 +180,7 @@ static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry) 
static inline struct dentry *ovl_do_tmpfile(struct dentry *dentry, umode_t mode)

{

	struct dentry *ret = vfs_tmpfile(dentry, mode, 0);

	int err = IS_ERR(ret) ? PTR_ERR(ret) : 0;

	int err = PTR_ERR_OR_ZERO(ret);



	pr_debug("tmpfile(%pd2, 0%o) = %i\n", dentry, mode, err);

	return ret;