b3c50e391ac6aa2ce50d89cd3bbf0079df8c3ff086ee2ff6d0d0c6e4.patch

From c1a808b07ff2933b8129e4c3c86925bcb271a9d9 Mon Sep 17 00:00:00 2001
From: Mark Salyzyn <salyzyn@android.com>
Date: Mon, 15 Jul 2019 15:46:45 -0700
Subject: [PATCH] FROMLIST: overlayfs: handle XATTR_NOSECURITY flag for get
 xattr method

Because of the overlayfs getxattr recursion, the incoming inode fails
to update the selinux sid resulting in avc denials being reported
against a target context of u:object_r:unlabeled:s0.

Solution is to respond to the XATTR_NOSECURITY flag in get xattr
method that calls the __vfs_getxattr handler instead so that the
context can be read in, rather than being denied with an -EACCES
when vfs_getxattr handler is called.

For the use case where access is to be blocked by the security layer.

The path then would be security(dentry) ->
__vfs_getxattr({dentry...XATTR_NOSECURITY}) ->
handler->get({dentry...XATTR_NOSECURITY}) ->
__vfs_getxattr({realdentry...XATTR_NOSECURITY}) ->
lower_handler->get({realdentry...XATTR_NOSECURITY}) which
would report back through the chain data and success as expected,
the logging security layer at the top would have the data to
determine the access permissions and report back to the logs and
the caller that the target context was blocked.

For selinux this would solve the cosmetic issue of the selinux log
and allow audit2allow to correctly report the rule needed to address
the access problem.

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 pick from https://lore.kernel.org/lkml/20191104215253.141818-3-salyzyn@android.com/)
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 133515582
Bug: 136124883
Bug: 129319403
Change-Id: Ia39543c5ce617976f14d790fb88e471d575ffd65

[rebase515(groeck): __vfs_getxattr() has an additional argument]

Signed-off-by: Guenter Roeck <groeck@chromium.org>

[rebase61(tzungbi):
    Squashed:
	FIXUP: FROMLIST: overlayfs: handle XATTR_NOSECURITY flag for get xattr method
    Fixed context conflicts.
]
Signed-off-by: Tzung-Bi Shih <tzungbi@chromium.org>
---
 fs/overlayfs/inode.c     | 5 +++--
 fs/overlayfs/overlayfs.h | 2 +-
 fs/overlayfs/super.c     | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 541cf3717fc2b1d1ce709d3725d9fd4307bf4cd1..797ae52cba1a9d6f740967c9ce3273d116f42f2f 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -395,7 +395,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 }
 
 int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
-		  void *value, size_t size)
+		  void *value, size_t size, int flags)
 {
 	ssize_t res;
 	const struct cred *old_cred;
@@ -403,7 +403,8 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 
 	ovl_i_path_real(inode, &realpath);
 	old_cred = ovl_override_creds(dentry->d_sb);
-	res = vfs_getxattr(mnt_idmap(realpath.mnt), realpath.dentry, name, value, size);
+	res = __vfs_getxattr(mnt_idmap(realpath.mnt), realpath.dentry,
+			     d_inode(realpath.dentry), name, value, size, flags);
 	revert_creds(old_cred);
 	return res;
 }
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 4d0b278f5630ea9a4d1b4f62277cb9646e128d57..1ccec5b8b6c91d25b4dfe5a3bf2c386b3338c937 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -606,7 +606,7 @@ int ovl_permission(struct mnt_idmap *idmap, struct inode *inode,
 int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 		  const void *value, size_t size, int flags);
 int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
-		  void *value, size_t size);
+		  void *value, size_t size, int flags);
 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
 
 #ifdef CONFIG_FS_POSIX_ACL
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index f1d9f75f8786ce51ae60723eff63dac5b59c9f7f..d77a5381ebdf1aa5630402967877a943edd27218 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1024,7 +1024,7 @@ static int ovl_other_xattr_get(const struct xattr_handler *handler,
 			       struct dentry *dentry, struct inode *inode,
 			       const char *name, void *buffer, size_t size)
 {
-	return ovl_xattr_get(dentry, inode, name, buffer, size);
+	return ovl_xattr_get(dentry, inode, name, buffer, size, flags);
 }
 
 static int ovl_other_xattr_set(const struct xattr_handler *handler,
-- 
2.38.3