59d228ecd19eb599282329017a403635a9a4baaa6d2238abfd510cd9.patch

From 7310758852b8dab0d4b09c97ddf5685c923ca397 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>
---
 fs/overlayfs/inode.c     | 5 +++--
 fs/overlayfs/overlayfs.h | 2 +-
 fs/overlayfs/super.c     | 4 ++--
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 9e61511de7a7c6c7c0311df10a0e6741623025d6..225c7c969ff4cddff1970c31818c1f6934d0f5fe 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -393,7 +393,7 @@ 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;
@@ -401,7 +401,8 @@ 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_user_ns(realpath.mnt), realpath.dentry, name, value, size);
+	res = __vfs_getxattr(&init_user_ns, realdentry, d_inode(realdentry), name,
+			     value, size, flags);
 	revert_creds(old_cred);
 	return res;
 }
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index eee8f08d32b639b1fe69fe28fae89353d060666e..e0b1be4e531e6c305dfe24b29334da485067c55c 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -590,7 +590,7 @@ int ovl_permission(struct user_namespace *mnt_userns, 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 a29a8afe9b26226dd94423e75d3287294a18e25b..dae5c2ec6327a15971d7c62eee23209860280b26 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1006,7 +1006,7 @@ ovl_posix_acl_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, handler->name, buffer, size);
+	return ovl_xattr_get(dentry, inode, handler->name, buffer, size, flags);
 }
 
 static int __maybe_unused
@@ -1098,7 +1098,7 @@ 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,
-- 
2.38.1.584.g0f3c55d4c2-goog