From b8095b679df854749a38240b3ca85156297e0184 Mon Sep 17 00:00:00 2001
From: Mark Salyzyn <salyzyn@android.com>
Date: Tue, 23 Jul 2019 13:53:48 -0700
Subject: [PATCH] FROMLIST: overlayfs: internal getxattr operations without
 sepolicy checking

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

(cherry picked from https://lore.kernel.org/lkml/20191104215253.141818-4-salyzyn@android.com/)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 133515582
Bug: 136124883
Bug: 129319403
Change-Id: I34d99cc46e9e87a79efc8d05f85980bbc137f7eb
[maennich: folded 8d5dc2cf06e9 ("ANDROID: overlayfs: fixup after upstream merge")]
Signed-off-by: Matthias Maennich <maennich@google.com>
---
 fs/overlayfs/namei.c     | 7 ++++---
 fs/overlayfs/overlayfs.h | 3 ++-
 fs/overlayfs/util.c      | 8 ++++----
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 210cd6f66e28..50616fd6743d 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -108,7 +108,8 @@ int ovl_check_fb_len(struct ovl_fb *fb, int fb_len)
 static struct ovl_fh *ovl_get_fh(struct ovl_fs *ofs, struct dentry *dentry,
 				 enum ovl_xattr ox)
 {
-	int res, err;
+	ssize_t res;
+	int err;
 	struct ovl_fh *fh = NULL;
 
 	res = ovl_do_getxattr(ofs, dentry, ox, NULL, 0);
@@ -143,10 +144,10 @@ static struct ovl_fh *ovl_get_fh(struct ovl_fs *ofs, struct dentry *dentry,
 	return NULL;
 
 fail:
-	pr_warn_ratelimited("failed to get origin (%i)\n", res);
+	pr_warn_ratelimited("failed to get origin (%zi)\n", res);
 	goto out;
 invalid:
-	pr_warn_ratelimited("invalid origin (%*phN)\n", res, fh);
+	pr_warn_ratelimited("invalid origin (%*phN)\n", (int)res, fh);
 	goto out;
 }
 
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 100898213d63..5d1cbed5cabc 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -186,7 +186,8 @@ static inline ssize_t ovl_do_getxattr(struct ovl_fs *ofs, struct dentry *dentry,
 				      size_t size)
 {
 	const char *name = ovl_xattr(ofs, ox);
-	int err = vfs_getxattr(&init_user_ns, dentry, name, value, size);
+	struct inode *ip = d_inode(dentry);
+	int err = __vfs_getxattr(dentry, ip, name, value, size, XATTR_NOSECURITY);
 	int len = (value && err > 0) ? err : 0;
 
 	pr_debug("getxattr(%pd2, \"%s\", \"%*pE\", %zu, 0) = %i\n",
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index b9d03627f364..417cbd13dd9a 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -551,7 +551,7 @@ void ovl_copy_up_end(struct dentry *dentry)
 
 bool ovl_check_origin_xattr(struct ovl_fs *ofs, struct dentry *dentry)
 {
-	int res;
+	ssize_t res;
 
 	res = ovl_do_getxattr(ofs, dentry, OVL_XATTR_ORIGIN, NULL, 0);
 
@@ -565,7 +565,7 @@ bool ovl_check_origin_xattr(struct ovl_fs *ofs, struct dentry *dentry)
 bool ovl_check_dir_xattr(struct super_block *sb, struct dentry *dentry,
 			 enum ovl_xattr ox)
 {
-	int res;
+	ssize_t res;
 	char val;
 
 	if (!d_is_dir(dentry))
@@ -861,7 +861,7 @@ int ovl_lock_rename_workdir(struct dentry *workdir, struct dentry *upperdir)
 /* err < 0, 0 if no metacopy xattr, 1 if metacopy xattr found */
 int ovl_check_metacopy_xattr(struct ovl_fs *ofs, struct dentry *dentry)
 {
-	int res;
+	ssize_t res;
 
 	/* Only regular files can have metacopy xattr */
 	if (!S_ISREG(d_inode(dentry)->i_mode))
@@ -883,7 +883,7 @@ int ovl_check_metacopy_xattr(struct ovl_fs *ofs, struct dentry *dentry)
 
 	return 1;
 out:
-	pr_warn_ratelimited("failed to get metacopy (%i)\n", res);
+	pr_warn_ratelimited("failed to get metacopy (%zi)\n", res);
 	return res;
 }
 
-- 
2.17.1