[PATCH 4.19 049/205] ovl: automatically enable redirect_dir on metacopy=on

Greg Kroah-Hartman
2018-11-19T16:32:18Z

From: Miklos Szeredi <mszeredi@redhat.com>

commit d47748e5ae5af6572e520cc9767bbe70c22ea498 upstream.

Current behavior is to automatically disable metacopy if redirect_dir is
not enabled and proceed with the mount.

If "metacopy=on" mount option was given, then this behavior can confuse the
user: no mount failure, yet metacopy is disabled.

This patch makes metacopy=on imply redirect_dir=on.

The converse is also true: turning off full redirect with redirect_dir=
{off|follow|nofollow} will disable metacopy.

If both metacopy=on and redirect_dir={off|follow|nofollow} is specified,
then mount will fail, since there's no way to correctly resolve the
conflict.

Reported-by: Daniel Walsh <dwalsh@redhat.com>
Fixes: d5791044d2e5 ("ovl: Provide a mount option metacopy=on/off...")
Cc: <stable@vger.kernel.org> # v4.19
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
Documentation/filesystems/overlayfs.txt | 6 +++++
fs/overlayfs/super.c | 36 +++++++++++++++++++++++++-------
2 files changed, 35 insertions(+), 7 deletions(-)

--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -286,6 +286,12 @@ pointed by REDIRECT. This should not be
"trusted." xattrs will require CAP_SYS_ADMIN. But it should be possible
for untrusted layers like from a pen drive.

+Note: redirect_dir={off|nofollow|follow(*)} conflicts with metacopy=on, and
+results in an error.
+
+(*) redirect_dir=follow only conflicts with metacopy=on if upperdir=... is
+given.
+
Sharing and copying layers
--------------------------

--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -472,6 +472,7 @@ static int ovl_parse_opt(char *opt, stru
{
char *p;
int err;
+ bool metacopy_opt = false, redirect_opt = false;

config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
if (!config->redirect_mode)
@@ -516,6 +517,7 @@ static int ovl_parse_opt(char *opt, stru
config->redirect_mode = match_strdup(&args[0]);
if (!config->redirect_mode)
return -ENOMEM;
+ redirect_opt = true;
break;

case OPT_INDEX_ON:
@@ -548,6 +550,7 @@ static int ovl_parse_opt(char *opt, stru

case OPT_METACOPY_ON:
config->metacopy = true;
+ metacopy_opt = true;
break;

case OPT_METACOPY_OFF:
@@ -572,13 +575,32 @@ static int ovl_parse_opt(char *opt, stru
if (err)
return err;

- /* metacopy feature with upper requires redirect_dir=on */
- if (config->upperdir && config->metacopy && !config->redirect_dir) {
- pr_warn("overlayfs: metadata only copy up requires \"redirect_dir=on\", falling back to metacopy=off.\n");
- config->metacopy = false;
- } else if (config->metacopy && !config->redirect_follow) {
- pr_warn("overlayfs: metadata only copy up requires \"redirect_dir=follow\" on non-upper mount, falling back to metacopy=off.\n");
- config->metacopy = false;
+ /*
+ * This is to make the logic below simpler. It doesn't make any other
+ * difference, since config->redirect_dir is only used for upper.
+ */
+ if (!config->upperdir && config->redirect_follow)
+ config->redirect_dir = true;
+
+ /* Resolve metacopy -> redirect_dir dependency */
+ if (config->metacopy && !config->redirect_dir) {
+ if (metacopy_opt && redirect_opt) {
+ pr_err("overlayfs: conflicting options: metacopy=on,redirect_dir=%s\n",
+ config->redirect_mode);
+ return -EINVAL;
+ }
+ if (redirect_opt) {
+ /*
+ * There was an explicit redirect_dir=... that resulted
+ * in this conflict.
+ */
+ pr_info("overlayfs: disabling metacopy due to redirect_dir=%s\n",
+ config->redirect_mode);
+ config->metacopy = false;
+ } else {
+ /* Automatically enable redirect otherwise. */
+ config->redirect_follow = config->redirect_dir = true;
+ }
}

return 0;