diff mbox series

[xenial:linux-azure] UBUNTU: SAUCE: overlayfs: internal getxattr operations without sepolicy checking

Message ID 20200326145111.1798-2-marcelo.cerri@canonical.com
State New
Headers show
Series [xenial:linux-azure] UBUNTU: SAUCE: overlayfs: internal getxattr operations without sepolicy checking | expand

Commit Message

Marcelo Henrique Cerri March 26, 2020, 2:51 p.m. UTC
From: Mark Salyzyn <salyzyn@android.com>

BugLink: https://bugs.launchpad.net/bugs/1864669

[Based on v15: https://lore.kernel.org/patchwork/patch/1148514/]

Check impure, opaque, origin & meta xattr with no sepolicy audit
(using __vfs_getxattr) since these operations are internal to
overlayfs operations and do not disclose any data.  This became
an issue for credential override off since sys_admin would have
been required by the caller; whereas would have been inherently
present for the creator since it performed the mount.

This is a change in operations since we do not check in the new
ovl_do_vfs_getxattr function if the credential override is off or
not.  Reasoning is that the sepolicy check is unnecessary overhead,
especially since the check can be expensive.

Because for override credentials off, this affects _everyone_ that
underneath performs private xattr calls without the appropriate
sepolicy permissions and sys_admin capability.  Providing blanket
support for sys_admin would be bad for all possible callers.

For the override credentials on, this will affect only the mounter,
should it lack sepolicy permissions. Not considered a security
problem since mounting by definition has sys_admin capabilities,
but sepolicy contexts would still need to be crafted.

It should be noted that there is precedence, __vfs_getxattr is used
in other filesystems for their own internal trusted xattr management.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: linux-unionfs@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@android.com
Cc: linux-security-module@vger.kernel.org

v15 - revert to v13 as xattr_gs_args was rejected.
    - move ovl_do_wrapper from util.c to inline in overlayfs.h

v14 - rebase to use xattr_gs_args.

v13 - rebase to use __vfs_getxattr flags option

v12 - rebase

v11 - switch name to ovl_do_vfs_getxattr, fortify comment

v10 - added to patch series

[marcelo.cerri@canonical.com: Ignored missing context, adjusted
 arguments for __vfs_getxattr and ovl_do_vfs_getxattr]
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
---
 fs/overlayfs/namei.c     | 19 ++++++++++---------
 fs/overlayfs/overlayfs.h |  7 +++++++
 fs/overlayfs/util.c      |  8 ++++----
 3 files changed, 21 insertions(+), 13 deletions(-)
diff mbox series

Patch

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index ae683af0f5e3..53cb05ed2625 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -28,10 +28,10 @@  struct ovl_lookup_data {
 static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
 			      size_t prelen, const char *post)
 {
-	int res;
+	ssize_t res;
 	char *s, *next, *buf = NULL;
 
-	res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
+	res = ovl_do_vfs_getxattr(dentry, OVL_XATTR_REDIRECT, NULL, 0);
 	if (res < 0) {
 		if (res == -ENODATA || res == -EOPNOTSUPP)
 			return 0;
@@ -44,7 +44,7 @@  static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
 	if (res == 0)
 		goto invalid;
 
-	res = vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
+	res = ovl_do_vfs_getxattr(dentry, OVL_XATTR_REDIRECT, buf, res);
 	if (res < 0)
 		goto fail;
 	if (res == 0)
@@ -84,7 +84,7 @@  static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
 	kfree(buf);
 	return 0;
 fail:
-	pr_warn_ratelimited("overlayfs: failed to get redirect (%i)\n", res);
+	pr_warn_ratelimited("overlayfs: failed to get redirect (%zi)\n", res);
 	goto err_free;
 invalid:
 	pr_warn_ratelimited("overlayfs: invalid redirect (%s)\n", buf);
@@ -98,10 +98,10 @@  static int ovl_acceptable(void *ctx, struct dentry *dentry)
 
 static struct ovl_fh *ovl_get_origin_fh(struct dentry *dentry)
 {
-	int res;
+	ssize_t res;
 	struct ovl_fh *fh = NULL;
 
-	res = vfs_getxattr(dentry, OVL_XATTR_ORIGIN, NULL, 0);
+	res = ovl_do_vfs_getxattr(dentry, OVL_XATTR_ORIGIN, NULL, 0);
 	if (res < 0) {
 		if (res == -ENODATA || res == -EOPNOTSUPP)
 			return NULL;
@@ -115,7 +115,7 @@  static struct ovl_fh *ovl_get_origin_fh(struct dentry *dentry)
 	if (!fh)
 		return ERR_PTR(-ENOMEM);
 
-	res = vfs_getxattr(dentry, OVL_XATTR_ORIGIN, fh, res);
+	res = ovl_do_vfs_getxattr(dentry, OVL_XATTR_ORIGIN, fh, res);
 	if (res < 0)
 		goto fail;
 
@@ -141,10 +141,11 @@  static struct ovl_fh *ovl_get_origin_fh(struct dentry *dentry)
 	return NULL;
 
 fail:
-	pr_warn_ratelimited("overlayfs: failed to get origin (%i)\n", res);
+	pr_warn_ratelimited("overlayfs: failed to get origin (%zi)\n", res);
 	goto out;
 invalid:
-	pr_warn_ratelimited("overlayfs: invalid origin (%*phN)\n", res, fh);
+	pr_warn_ratelimited("overlayfs: invalid origin (%*phN)\n",
+			    (int)res, fh);
 	goto out;
 }
 
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 6fd160b3db8a..b3ae63f61605 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -198,6 +198,13 @@  static inline struct dentry *ovl_do_tmpfile(struct dentry *dentry, umode_t mode)
 	return ret;
 }
 
+static inline ssize_t ovl_do_vfs_getxattr(struct dentry *dentry,
+					  const char *name, void *buf,
+					  size_t size)
+{
+	return __vfs_getxattr(dentry, d_inode(dentry), name, buf, size);
+}
+
 /* util.c */
 int ovl_want_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 4b0d52cd7cf4..57d8ee84e657 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -348,9 +348,9 @@  void ovl_copy_up_end(struct dentry *dentry)
 
 bool ovl_check_origin_xattr(struct dentry *dentry)
 {
-	int res;
+	ssize_t res;
 
-	res = vfs_getxattr(dentry, OVL_XATTR_ORIGIN, NULL, 0);
+	res = ovl_do_vfs_getxattr(dentry, OVL_XATTR_ORIGIN, NULL, 0);
 
 	/* Zero size value means "copied up but origin unknown" */
 	if (res >= 0)
@@ -361,13 +361,13 @@  bool ovl_check_origin_xattr(struct dentry *dentry)
 
 bool ovl_check_dir_xattr(struct dentry *dentry, const char *name)
 {
-	int res;
+	ssize_t res;
 	char val;
 
 	if (!d_is_dir(dentry))
 		return false;
 
-	res = vfs_getxattr(dentry, name, &val, 1);
+	res = ovl_do_vfs_getxattr(dentry, name, &val, 1);
 	if (res == 1 && val == 'y')
 		return true;