[PATCH v15 0/4] overlayfs override_creds=off & nested get xattr fix

[PATCH v15 0/4] overlayfs override_creds=off & nested get xattr fix

[Mark Salyzyn]

Mark Salyzyn (3):
  Add flags option to get xattr method paired to __vfs_getxattr
  overlayfs: handle XATTR_NOSECURITY flag for get xattr method
  overlayfs: override_creds=off option bypass creator_cred

Mark Salyzyn + John Stultz (1):
  overlayfs: inode_owner_or_capable called during execv

The first three patches address fundamental security issues that should
be solved regardless of the override_creds=off feature.

The fourth adds the feature depends on these other fixes.

By default, all access to the upper, lower and work directories is the
recorded mounter's MAC and DAC credentials.  The incoming accesses are
checked against the caller's credentials.

If the principles of least privilege are applied for sepolicy, the
mounter's credentials might not overlap the credentials of the caller's
when accessing the overlayfs filesystem.  For example, a file that a
lower DAC privileged caller can execute, is MAC denied to the
generally higher DAC privileged mounter, to prevent an attack vector.

We add the option to turn off override_creds in the mount options; all
subsequent operations after mount on the filesystem will be only the
caller's credentials.  The module boolean parameter and mount option
override_creds is also added as a presence check for this "feature",
existence of /sys/module/overlay/parameters/overlay_creds

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: John Stultz <john.stultz@linaro.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
To: linux-fsdevel@vger.kernel.org
To: linux-unionfs@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Cc: kernel-team@android.com

---

v16
- rebase and merge of two patches.
- add adjustment to deal with execv when overrides is off.

v15
- Revert back to v4 with fixes from on the way from v5-v14. The single
  structure argument passing to address the complaints about too many
  arguments was rejected by the community.
- Drop the udner discussion fix for an additional CAP_DAC_READ_SEARCH
  check. Can address that independently.
- ToDo: upstream test frame for thes security fixes (currently testing
  is all in Android).

v14:
- Rejoin, rebase and a few adjustments.

v13:
- Pull out first patch and try to get it in alone feedback, some
  Acks, and then <crickets> because people forgot why we were doing i.

v12:
- Restore squished out patch 2 and 3 in the series,
  then change algorithm to add flags argument.
  Per-thread flag is a large security surface.

v11:
- Squish out v10 introduced patch 2 and 3 in the series,
  then and use per-thread flag instead for nesting.
- Switch name to ovl_do_vds_getxattr for __vds_getxattr wrapper.
- Add sb argument to ovl_revert_creds to match future work.

v10:
- Return NULL on CAP_DAC_READ_SEARCH
- Add __get xattr method to solve sepolicy logging issue
- Drop unnecessary sys_admin sepolicy checking for administrative
  driver internal xattr functions.

v6:
- Drop CONFIG_OVERLAY_FS_OVERRIDE_CREDS.
- Do better with the documentation, drop rationalizations.
- pr_warn message adjusted to report consequences.

v5:
- beefed up the caveats in the Documentation
- Is dependent on
  "overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh"
  "overlayfs: check CAP_MKNOD before issuing vfs_whiteout"
- Added prwarn when override_creds=off

v4:
- spelling and grammar errors in text

v3:
- Change name from caller_credentials / creator_credentials to the
  boolean override_creds.
- Changed from creator to mounter credentials.
- Updated and fortified the documentation.
- Added CONFIG_OVERLAY_FS_OVERRIDE_CREDS

v2:
- Forward port changed attr to stat, resulting in a build error.
- altered commit message.

 Documentation/filesystems/locking.rst   |  2 +-
 Documentation/filesystems/overlayfs.rst | 23 ++++++++++++++++
 fs/9p/acl.c                             |  3 ++-
 fs/9p/xattr.c                           |  3 ++-
 fs/afs/xattr.c                          | 10 +++----
 fs/btrfs/xattr.c                        |  3 ++-
 fs/ceph/xattr.c                         |  3 ++-
 fs/cifs/xattr.c                         |  2 +-
 fs/ecryptfs/inode.c                     |  6 +++--
 fs/ecryptfs/mmap.c                      |  2 +-
 fs/erofs/xattr.c                        |  3 ++-
 fs/ext2/xattr_security.c                |  2 +-
 fs/ext2/xattr_trusted.c                 |  2 +-
 fs/ext2/xattr_user.c                    |  2 +-
 fs/ext4/xattr_security.c                |  2 +-
 fs/ext4/xattr_trusted.c                 |  2 +-
 fs/ext4/xattr_user.c                    |  2 +-
 fs/f2fs/xattr.c                         |  4 +--
 fs/fuse/xattr.c                         |  4 +--
 fs/gfs2/xattr.c                         |  3 ++-
 fs/hfs/attr.c                           |  2 +-
 fs/hfsplus/xattr.c                      |  3 ++-
 fs/hfsplus/xattr_security.c             |  3 ++-
 fs/hfsplus/xattr_trusted.c              |  3 ++-
 fs/hfsplus/xattr_user.c                 |  3 ++-
 fs/jffs2/security.c                     |  3 ++-
 fs/jffs2/xattr_trusted.c                |  3 ++-
 fs/jffs2/xattr_user.c                   |  3 ++-
 fs/jfs/xattr.c                          |  5 ++--
 fs/kernfs/inode.c                       |  3 ++-
 fs/nfs/nfs4proc.c                       |  9 ++++---
 fs/ocfs2/xattr.c                        |  9 ++++---
 fs/orangefs/xattr.c                     |  3 ++-
 fs/overlayfs/copy_up.c                  |  2 +-
 fs/overlayfs/dir.c                      | 17 +++++++-----
 fs/overlayfs/file.c                     | 26 +++++++++---------
 fs/overlayfs/inode.c                    | 23 ++++++++--------
 fs/overlayfs/namei.c                    |  6 ++---
 fs/overlayfs/overlayfs.h                |  5 ++--
 fs/overlayfs/ovl_entry.h                |  1 +
 fs/overlayfs/readdir.c                  |  8 +++---
 fs/overlayfs/super.c                    | 34 ++++++++++++++++++-----
 fs/overlayfs/util.c                     | 13 +++++++--
 fs/posix_acl.c                          |  2 +-
 fs/reiserfs/xattr_security.c            |  3 ++-
 fs/reiserfs/xattr_trusted.c             |  3 ++-
 fs/reiserfs/xattr_user.c                |  3 ++-
 fs/squashfs/xattr.c                     |  2 +-
 fs/ubifs/xattr.c                        |  3 ++-
 fs/xattr.c                              | 36 ++++++++++++-------------
 fs/xfs/xfs_xattr.c                      |  3 ++-
 include/linux/xattr.h                   |  9 ++++---
 include/uapi/linux/xattr.h              |  7 +++--
 mm/shmem.c                              |  3 ++-
 net/socket.c                            |  3 ++-
 security/commoncap.c                    |  6 +++--
 security/integrity/evm/evm_main.c       |  3 ++-
 security/selinux/hooks.c                | 11 +++++---
 security/smack/smack_lsm.c              |  5 ++--
 59 files changed, 237 insertions(+), 135 deletions(-)

-- 
2.29.0.rc1.297.gfa9743e501-goog

[PATCH v16 2/4] overlayfs: handle XATTR_NOSECURITY flag for get xattr method

[Mark Salyzyn]

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.

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_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>
To: linux-fsdevel@vger.kernel.org
To: linux-unionfs@vger.kernel.org
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: linux-kernel@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Cc: kernel-team@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: linux-doc@vger.kernel.org
Cc: John Stultz <john.stultz@linaro.org>

v16 - rebase and merge internal getxattr operations patch

v15 - revert to v13 because xattr_gs_args rejected.

v14 - rebase to use xattr_gs_args.

v13 - rebase to use __vfs_getxattr flags option.

v12 - Added back to patch series as get xattr with flag option.

v11 - Squashed out of patch series and replaced with per-thread flag
      solution.

v10 - Added to patch series as __get xattr method.
---
 fs/overlayfs/inode.c     | 5 +++--
 fs/overlayfs/overlayfs.h | 4 ++--
 fs/overlayfs/super.c     | 4 ++--
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index b584dca845ba..2b14291beb86 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -378,7 +378,7 @@ 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;
@@ -386,7 +386,8 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 		ovl_i_dentry_upper(inode) ?: ovl_dentry_lower(dentry);
 
 	old_cred = ovl_override_creds(dentry->d_sb);
-	res = vfs_getxattr(realdentry, name, value, size);
+	res = __vfs_getxattr(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 f8880aa2ba0e..3033f0c4de5f 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -184,7 +184,7 @@ static inline ssize_t ovl_do_getxattr(struct ovl_fs *ofs, struct dentry *dentry,
 				      size_t size)
 {
 	const char *name = ovl_xattr(ofs, ox);
-	return vfs_getxattr(dentry, name, value, size);
+	return __vfs_getxattr(dentry, name, value, size, XATTR_NOSECURITY);
 }
 
 static inline int ovl_do_setxattr(struct ovl_fs *ofs, struct dentry *dentry,
@@ -439,7 +439,7 @@ int ovl_permission(struct inode *inode, int mask);
 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);
 struct posix_acl *ovl_get_acl(struct inode *inode, int type);
 int ovl_update_time(struct inode *inode, struct timespec64 *ts, int flags);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index f41353ba1e68..d447958badc2 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -930,7 +930,7 @@ ovl_posix_acl_xattr_get(const struct xattr_handler *handler,
 			struct dentry *dentry, struct inode *inode,
 			const char *name, void *buffer, size_t size, int flags)
 {
-	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
@@ -1012,7 +1012,7 @@ static int ovl_other_xattr_get(const struct xattr_handler *handler,
 			       const char *name, void *buffer, size_t size,
 			       int flags)
 {
-	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,
-- 
2.29.0.rc1.297.gfa9743e501-goog

[PATCH v16 3/4] overlayfs: override_creds=off option bypass creator_cred

[Mark Salyzyn]

By default, all access to the upper, lower and work directories is the
recorded mounter's MAC and DAC credentials.  The incoming accesses are
checked against the caller's credentials.

If the principles of least privilege are applied, the mounter's
credentials might not overlap the credentials of the caller's when
accessing the overlayfs filesystem.  For example, a file that a lower
DAC privileged caller can execute, is MAC denied to the generally
higher DAC privileged mounter, to prevent an attack vector.

We add the option to turn off override_creds in the mount options; all
subsequent operations after mount on the filesystem will be only the
caller's credentials.  The module boolean parameter and mount option
override_creds is also added as a presence check for this "feature",
existence of /sys/module/overlay/parameters/override_creds.

It was not always this way.  Circa 4.6 there was no recorded mounter's
credentials, instead privileged access to upper or work directories
were temporarily increased to perform the operations.  The MAC
(selinux) policies were caller's in all cases.  override_creds=off
partially returns us to this older access model minus the insecure
temporary credential increases.  This is to permit use in a system
with non-overlapping security models for each executable including
the agent that mounts the overlayfs filesystem.  In Android
this is the case since init, which performs the mount operations,
has a minimal MAC set of privileges to reduce any attack surface,
and services that use the content have a different set of MAC
privileges (eg: read, for vendor labelled configuration, execute for
vendor libraries and modules).  The caveats are not a problem in
the Android usage model, however they should be fixed for
completeness and for general use in time.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
To: linux-fsdevel@vger.kernel.org
To: linux-unionfs@vger.kernel.org
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: John Stultz <john.stultz@linaro.org>
Cc: linux-security-module@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: kernel-team@android.com

v16
- Rebase, cover a few more new ovl_revert_creds callpoints.

v15
- Rebase

v14:
- fix an issue in ovl_create_or_link which leaks credentials.

v12 + v13
- Rebase

v11:
- add sb argument to ovl_revert_creds to match future work in progress
  in other commiter's hands.

v10:
- Rebase (and expand because of increased revert_cred usage)

v9:
- Add to the caveats

v8:
- drop pr_warn message after straw poll to remove it.
- added a use case in the commit message

v7:
- change name of internal parameter to ovl_override_creds_def
- report override_creds only if different than default

v6:
- Drop CONFIG_OVERLAY_FS_OVERRIDE_CREDS.
- Do better with the documentation.
- pr_warn message adjusted to report consequences.

v5:
- beefed up the caveats in the Documentation
- Is dependent on
  "overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh"
  "overlayfs: check CAP_MKNOD before issuing vfs_whiteout"
- Added prwarn when override_creds=off

v4:
- spelling and grammar errors in text

v3:
- Change name from caller_credentials / creator_credentials to the
  boolean override_creds.
- Changed from creator to mounter credentials.
- Updated and fortified the documentation.
- Added CONFIG_OVERLAY_FS_OVERRIDE_CREDS

v2:
- Forward port changed attr to stat, resulting in a build error.
- altered commit message.
---
 Documentation/filesystems/overlayfs.rst | 23 +++++++++++++++++++++++
 fs/overlayfs/copy_up.c                  |  2 +-
 fs/overlayfs/dir.c                      | 17 ++++++++++-------
 fs/overlayfs/file.c                     | 24 ++++++++++++------------
 fs/overlayfs/inode.c                    | 18 +++++++++---------
 fs/overlayfs/namei.c                    |  6 +++---
 fs/overlayfs/overlayfs.h                |  1 +
 fs/overlayfs/ovl_entry.h                |  1 +
 fs/overlayfs/readdir.c                  |  8 ++++----
 fs/overlayfs/super.c                    | 22 +++++++++++++++++++++-
 fs/overlayfs/util.c                     | 13 +++++++++++--
 11 files changed, 96 insertions(+), 39 deletions(-)

diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
index 580ab9a0fe31..18ac7d35c145 100644
--- a/Documentation/filesystems/overlayfs.rst
+++ b/Documentation/filesystems/overlayfs.rst
@@ -137,6 +137,29 @@ Only the lists of names from directories are merged.  Other content
 such as metadata and extended attributes are reported for the upper
 directory only.  These attributes of the lower directory are hidden.
 
+credentials
+-----------
+
+By default, all access to the upper, lower and work directories is the
+recorded mounter's MAC and DAC credentials.  The incoming accesses are
+checked against the caller's credentials.
+
+In the case where caller MAC or DAC credentials do not overlap, a
+use case available in older versions of the driver, the
+override_creds mount flag can be turned off and help when the use
+pattern has caller with legitimate credentials where the mounter
+does not.  Several unintended side effects will occur though.  The
+caller without certain key capabilities or lower privilege will not
+always be able to delete files or directories, create nodes, or
+search some restricted directories.  The ability to search and read
+a directory entry is spotty as a result of the cache mechanism not
+retesting the credentials because of the assumption, a privileged
+caller can fill cache, then a lower privilege can read the directory
+cache.  The uneven security model where cache, upperdir and workdir
+are opened at privilege, but accessed without creating a form of
+privilege escalation, should only be used with strict understanding
+of the side effects and of the security policies.
+
 whiteouts and opaque directories
 --------------------------------
 
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 955ecd4030f0..b9d97e7efd5c 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -962,7 +962,7 @@ static int ovl_copy_up_flags(struct dentry *dentry, int flags)
 		dput(parent);
 		dput(next);
 	}
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 
 	return err;
 }
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 28a075b5f5b2..3c6f5f6648b8 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -565,7 +565,7 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
 			      struct ovl_cattr *attr, bool origin)
 {
 	int err;
-	const struct cred *old_cred;
+	const struct cred *old_cred, *hold_cred = NULL;
 	struct cred *override_cred;
 	struct dentry *parent = dentry->d_parent;
 
@@ -592,14 +592,15 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
 		override_cred->fsgid = inode->i_gid;
 		if (!attr->hardlink) {
 			err = security_dentry_create_files_as(dentry,
-					attr->mode, &dentry->d_name, old_cred,
+					attr->mode, &dentry->d_name,
+					old_cred ? old_cred : current_cred(),
 					override_cred);
 			if (err) {
 				put_cred(override_cred);
 				goto out_revert_creds;
 			}
 		}
-		put_cred(override_creds(override_cred));
+		hold_cred = override_creds(override_cred);
 		put_cred(override_cred);
 
 		if (!ovl_dentry_is_whiteout(dentry))
@@ -608,7 +609,9 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
 			err = ovl_create_over_whiteout(dentry, inode, attr);
 	}
 out_revert_creds:
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred ?: hold_cred);
+	if (old_cred && hold_cred)
+		put_cred(hold_cred);
 	return err;
 }
 
@@ -684,7 +687,7 @@ static int ovl_set_link_redirect(struct dentry *dentry)
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	err = ovl_set_redirect(dentry, false);
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 
 	return err;
 }
@@ -903,7 +906,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
 		err = ovl_remove_upper(dentry, is_dir, &list);
 	else
 		err = ovl_remove_and_whiteout(dentry, &list);
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 	if (!err) {
 		if (is_dir)
 			clear_nlink(dentry->d_inode);
@@ -1273,7 +1276,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *old,
 out_unlock:
 	unlock_rename(new_upperdir, old_upperdir);
 out_revert_creds:
-	revert_creds(old_cred);
+	ovl_revert_creds(old->d_sb, old_cred);
 	if (update_nlink)
 		ovl_nlink_end(new);
 out_drop_write:
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index efccb7c1f9bc..b1357bb067d9 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -59,7 +59,7 @@ static struct file *ovl_open_realfile(const struct file *file,
 		realfile = open_with_fake_path(&file->f_path, flags, realinode,
 					       current_cred());
 	}
-	revert_creds(old_cred);
+	ovl_revert_creds(inode->i_sb, old_cred);
 
 	pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n",
 		 file, file, ovl_whatisit(inode, realinode), file->f_flags,
@@ -209,7 +209,7 @@ static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
 
 	old_cred = ovl_override_creds(inode->i_sb);
 	ret = vfs_llseek(real.file, offset, whence);
-	revert_creds(old_cred);
+	ovl_revert_creds(inode->i_sb, old_cred);
 
 	file->f_pos = real.file->f_pos;
 	ovl_inode_unlock(inode);
@@ -323,7 +323,7 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter)
 			ovl_aio_cleanup_handler(aio_req);
 	}
 out:
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
 	ovl_file_accessed(file);
 
 	fdput(real);
@@ -388,7 +388,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 			ovl_aio_cleanup_handler(aio_req);
 	}
 out:
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
 	fdput(real);
 
 out_unlock:
@@ -411,7 +411,7 @@ static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
 
 	old_cred = ovl_override_creds(file_inode(in)->i_sb);
 	ret = generic_file_splice_read(real.file, ppos, pipe, len, flags);
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(in)->i_sb, old_cred);
 
 	ovl_file_accessed(in);
 	fdput(real);
@@ -432,7 +432,7 @@ ovl_splice_write(struct pipe_inode_info *pipe, struct file *out,
 
 	old_cred = ovl_override_creds(file_inode(out)->i_sb);
 	ret = iter_file_splice_write(pipe, real.file, ppos, len, flags);
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(out)->i_sb, old_cred);
 
 	ovl_file_accessed(out);
 	fdput(real);
@@ -456,7 +456,7 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) {
 		old_cred = ovl_override_creds(file_inode(file)->i_sb);
 		ret = vfs_fsync_range(real.file, start, end, datasync);
-		revert_creds(old_cred);
+		ovl_revert_creds(file_inode(file)->i_sb, old_cred);
 	}
 
 	fdput(real);
@@ -480,7 +480,7 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = call_mmap(vma->vm_file, vma);
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
 
 	if (ret) {
 		/* Drop reference count from new vm_file value */
@@ -508,7 +508,7 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = vfs_fallocate(real.file, mode, offset, len);
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
 
 	/* Update size */
 	ovl_copyattr(ovl_inode_real(inode), inode);
@@ -530,7 +530,7 @@ static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = vfs_fadvise(real.file, offset, len, advice);
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
 
 	fdput(real);
 
@@ -552,7 +552,7 @@ static long ovl_real_ioctl(struct file *file, unsigned int cmd,
 	ret = security_file_ioctl(real.file, cmd, arg);
 	if (!ret)
 		ret = vfs_ioctl(real.file, cmd, arg);
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
 
 	fdput(real);
 
@@ -741,7 +741,7 @@ static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 						flags);
 		break;
 	}
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(file_out)->i_sb, old_cred);
 
 	/* Update size */
 	ovl_copyattr(ovl_inode_real(inode_out), inode_out);
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 2b14291beb86..fb0ec01774e6 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -80,7 +80,7 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr)
 		inode_lock(upperdentry->d_inode);
 		old_cred = ovl_override_creds(dentry->d_sb);
 		err = notify_change(upperdentry, attr, NULL);
-		revert_creds(old_cred);
+		ovl_revert_creds(dentry->d_sb, old_cred);
 		if (!err)
 			ovl_copyattr(upperdentry->d_inode, dentry->d_inode);
 		inode_unlock(upperdentry->d_inode);
@@ -272,7 +272,7 @@ int ovl_getattr(const struct path *path, struct kstat *stat,
 		stat->nlink = dentry->d_inode->i_nlink;
 
 out:
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 
 	return err;
 }
@@ -306,7 +306,7 @@ int ovl_permission(struct inode *inode, int mask)
 		mask |= MAY_READ;
 	}
 	err = inode_permission(realinode, mask);
-	revert_creds(old_cred);
+	ovl_revert_creds(inode->i_sb, old_cred);
 
 	return err;
 }
@@ -323,7 +323,7 @@ static const char *ovl_get_link(struct dentry *dentry,
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	p = vfs_get_link(ovl_dentry_real(dentry), done);
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 	return p;
 }
 
@@ -366,7 +366,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
 		WARN_ON(flags != XATTR_REPLACE);
 		err = vfs_removexattr(realdentry, name);
 	}
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 
 	/* copy c/mtime */
 	ovl_copyattr(d_inode(realdentry), inode);
@@ -388,7 +388,7 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name,
 	old_cred = ovl_override_creds(dentry->d_sb);
 	res = __vfs_getxattr(realdentry, d_inode(realdentry), name,
 			     value, size, flags);
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 	return res;
 }
 
@@ -416,7 +416,7 @@ ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	res = vfs_listxattr(realdentry, list, size);
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 	if (res <= 0 || size == 0)
 		return res;
 
@@ -451,7 +451,7 @@ struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 
 	old_cred = ovl_override_creds(inode->i_sb);
 	acl = get_acl(realinode, type);
-	revert_creds(old_cred);
+	ovl_revert_creds(inode->i_sb, old_cred);
 
 	return acl;
 }
@@ -485,7 +485,7 @@ static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 
 	old_cred = ovl_override_creds(inode->i_sb);
 	err = realinode->i_op->fiemap(realinode, fieinfo, start, len);
-	revert_creds(old_cred);
+	ovl_revert_creds(inode->i_sb, old_cred);
 
 	return err;
 }
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index a6162c4076db..0e6290844c57 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -1097,7 +1097,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	ovl_dentry_update_reval(dentry, upperdentry,
 			DCACHE_OP_REVALIDATE | DCACHE_OP_WEAK_REVALIDATE);
 
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 	if (origin_path) {
 		dput(origin_path->dentry);
 		kfree(origin_path);
@@ -1124,7 +1124,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 	kfree(upperredirect);
 out:
 	kfree(d.redirect);
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 	return ERR_PTR(err);
 }
 
@@ -1176,7 +1176,7 @@ bool ovl_lower_positive(struct dentry *dentry)
 			dput(this);
 		}
 	}
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 
 	return positive;
 }
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 3033f0c4de5f..5840d817e8e4 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -251,6 +251,7 @@ int ovl_want_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);
 struct dentry *ovl_workdir(struct dentry *dentry);
 const struct cred *ovl_override_creds(struct super_block *sb);
+void ovl_revert_creds(struct super_block *sb, const struct cred *oldcred);
 int ovl_can_decode_fh(struct super_block *sb);
 struct dentry *ovl_indexdir(struct super_block *sb);
 bool ovl_index_all(struct super_block *sb);
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 1b5a2094df8e..597f00982ade 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -18,6 +18,7 @@ struct ovl_config {
 	int xino;
 	bool metacopy;
 	bool ovl_volatile;
+	bool override_creds;
 };
 
 struct ovl_sb {
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 01620ebae1bd..38d5b855c4a4 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -286,7 +286,7 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
 		}
 		inode_unlock(dir->d_inode);
 	}
-	revert_creds(old_cred);
+	ovl_revert_creds(rdd->dentry->d_sb, old_cred);
 
 	return err;
 }
@@ -796,7 +796,7 @@ static int ovl_iterate(struct file *file, struct dir_context *ctx)
 	}
 	err = 0;
 out:
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 	return err;
 }
 
@@ -848,7 +848,7 @@ static struct file *ovl_dir_open_realfile(const struct file *file,
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	res = ovl_path_open(realpath, O_RDONLY | (file->f_flags & O_LARGEFILE));
-	revert_creds(old_cred);
+	ovl_revert_creds(file_inode(file)->i_sb, old_cred);
 
 	return res;
 }
@@ -986,7 +986,7 @@ int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	err = ovl_dir_read_merged(dentry, list, &root);
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 	if (err)
 		return err;
 
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index d447958badc2..28c5d291f836 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -53,6 +53,11 @@ module_param_named(xino_auto, ovl_xino_auto_def, bool, 0644);
 MODULE_PARM_DESC(xino_auto,
 		 "Auto enable xino feature");
 
+static bool __read_mostly ovl_override_creds_def = true;
+module_param_named(override_creds, ovl_override_creds_def, bool, 0644);
+MODULE_PARM_DESC(ovl_override_creds_def,
+		 "Use mounter's credentials for accesses");
+
 static void ovl_entry_stack_free(struct ovl_entry *oe)
 {
 	unsigned int i;
@@ -366,6 +371,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
 			   ofs->config.metacopy ? "on" : "off");
 	if (ofs->config.ovl_volatile)
 		seq_puts(m, ",volatile");
+	if (ofs->config.override_creds != ovl_override_creds_def)
+		seq_show_option(m, "override_creds",
+				ofs->config.override_creds ? "on" : "off");
 	return 0;
 }
 
@@ -418,6 +426,8 @@ enum {
 	OPT_METACOPY_ON,
 	OPT_METACOPY_OFF,
 	OPT_VOLATILE,
+	OPT_OVERRIDE_CREDS_ON,
+	OPT_OVERRIDE_CREDS_OFF,
 	OPT_ERR,
 };
 
@@ -437,6 +447,8 @@ static const match_table_t ovl_tokens = {
 	{OPT_METACOPY_ON,		"metacopy=on"},
 	{OPT_METACOPY_OFF,		"metacopy=off"},
 	{OPT_VOLATILE,			"volatile"},
+	{OPT_OVERRIDE_CREDS_ON,		"override_creds=on"},
+	{OPT_OVERRIDE_CREDS_OFF,	"override_creds=off"},
 	{OPT_ERR,			NULL}
 };
 
@@ -496,6 +508,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 	config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
 	if (!config->redirect_mode)
 		return -ENOMEM;
+	config->override_creds = ovl_override_creds_def;
 
 	while ((p = ovl_next_opt(&opt)) != NULL) {
 		int token;
@@ -585,6 +598,14 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			config->ovl_volatile = true;
 			break;
 
+		case OPT_OVERRIDE_CREDS_ON:
+			config->override_creds = true;
+			break;
+
+		case OPT_OVERRIDE_CREDS_OFF:
+			config->override_creds = false;
+			break;
+
 		default:
 			pr_err("unrecognized mount option \"%s\" or missing value\n",
 					p);
@@ -2007,7 +2028,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	kfree(splitlower);
 
 	sb->s_root = root_dentry;
-
 	return 0;
 
 out_free_oe:
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 23f475627d07..8d1e7f0db7bc 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -37,9 +37,18 @@ const struct cred *ovl_override_creds(struct super_block *sb)
 {
 	struct ovl_fs *ofs = sb->s_fs_info;
 
+	if (!ofs->config.override_creds)
+		return NULL;
 	return override_creds(ofs->creator_cred);
 }
 
+void ovl_revert_creds(struct super_block *sb, const struct cred *old_cred)
+{
+	if (old_cred)
+		revert_creds(old_cred);
+}
+
+
 /*
  * Check if underlying fs supports file handles and try to determine encoding
  * type, in order to deduce maximum inode number used by fs.
@@ -823,7 +832,7 @@ int ovl_nlink_start(struct dentry *dentry)
 	 * value relative to the upper inode nlink in an upper inode xattr.
 	 */
 	err = ovl_set_nlink_upper(dentry);
-	revert_creds(old_cred);
+	ovl_revert_creds(dentry->d_sb, old_cred);
 
 out:
 	if (err)
@@ -841,7 +850,7 @@ void ovl_nlink_end(struct dentry *dentry)
 
 		old_cred = ovl_override_creds(dentry->d_sb);
 		ovl_cleanup_index(dentry);
-		revert_creds(old_cred);
+		ovl_revert_creds(dentry->d_sb, old_cred);
 	}
 
 	ovl_inode_unlock(inode);
-- 
2.29.0.rc1.297.gfa9743e501-goog

Re: [PATCH v16 3/4] overlayfs: override_creds=off option bypass creator_cred

[Amir Goldstein]

On Mon, Oct 19, 2020 at 2:53 PM Mark Salyzyn <salyzyn@android.com> wrote:
>
> By default, all access to the upper, lower and work directories is the
> recorded mounter's MAC and DAC credentials.  The incoming accesses are
> checked against the caller's credentials.
>
> If the principles of least privilege are applied, the mounter's
> credentials might not overlap the credentials of the caller's when
> accessing the overlayfs filesystem.  For example, a file that a lower
> DAC privileged caller can execute, is MAC denied to the generally
> higher DAC privileged mounter, to prevent an attack vector.
>
> We add the option to turn off override_creds in the mount options; all
> subsequent operations after mount on the filesystem will be only the
> caller's credentials.  The module boolean parameter and mount option
> override_creds is also added as a presence check for this "feature",
> existence of /sys/module/overlay/parameters/override_creds.
>
> It was not always this way.  Circa 4.6 there was no recorded mounter's
> credentials, instead privileged access to upper or work directories
> were temporarily increased to perform the operations.  The MAC
> (selinux) policies were caller's in all cases.  override_creds=off
> partially returns us to this older access model minus the insecure
> temporary credential increases.  This is to permit use in a system
> with non-overlapping security models for each executable including
> the agent that mounts the overlayfs filesystem.  In Android
> this is the case since init, which performs the mount operations,
> has a minimal MAC set of privileges to reduce any attack surface,
> and services that use the content have a different set of MAC
> privileges (eg: read, for vendor labelled configuration, execute for
> vendor libraries and modules).  The caveats are not a problem in
> the Android usage model, however they should be fixed for
> completeness and for general use in time.
>
> Signed-off-by: Mark Salyzyn <salyzyn@android.com>
> To: linux-fsdevel@vger.kernel.org
> To: linux-unionfs@vger.kernel.org
> 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: John Stultz <john.stultz@linaro.org>
> Cc: linux-security-module@vger.kernel.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: kernel-team@android.com
>

Please CC <linux-unionfs@vger.kernel.org> for overlayfs patches

> v16
> - Rebase, cover a few more new ovl_revert_creds callpoints.
>
> v15
> - Rebase
>
> v14:
> - fix an issue in ovl_create_or_link which leaks credentials.
>
> v12 + v13
> - Rebase
>
> v11:
> - add sb argument to ovl_revert_creds to match future work in progress
>   in other commiter's hands.
>
> v10:
> - Rebase (and expand because of increased revert_cred usage)
>
> v9:
> - Add to the caveats
>
> v8:
> - drop pr_warn message after straw poll to remove it.
> - added a use case in the commit message
>
> v7:
> - change name of internal parameter to ovl_override_creds_def
> - report override_creds only if different than default
>
> v6:
> - Drop CONFIG_OVERLAY_FS_OVERRIDE_CREDS.
> - Do better with the documentation.
> - pr_warn message adjusted to report consequences.
>
> v5:
> - beefed up the caveats in the Documentation
> - Is dependent on
>   "overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh"
>   "overlayfs: check CAP_MKNOD before issuing vfs_whiteout"
> - Added prwarn when override_creds=off
>
> v4:
> - spelling and grammar errors in text
>
> v3:
> - Change name from caller_credentials / creator_credentials to the
>   boolean override_creds.
> - Changed from creator to mounter credentials.
> - Updated and fortified the documentation.
> - Added CONFIG_OVERLAY_FS_OVERRIDE_CREDS
>
> v2:
> - Forward port changed attr to stat, resulting in a build error.
> - altered commit message.
> ---
>  Documentation/filesystems/overlayfs.rst | 23 +++++++++++++++++++++++
>  fs/overlayfs/copy_up.c                  |  2 +-
>  fs/overlayfs/dir.c                      | 17 ++++++++++-------
>  fs/overlayfs/file.c                     | 24 ++++++++++++------------
>  fs/overlayfs/inode.c                    | 18 +++++++++---------
>  fs/overlayfs/namei.c                    |  6 +++---
>  fs/overlayfs/overlayfs.h                |  1 +
>  fs/overlayfs/ovl_entry.h                |  1 +
>  fs/overlayfs/readdir.c                  |  8 ++++----
>  fs/overlayfs/super.c                    | 22 +++++++++++++++++++++-
>  fs/overlayfs/util.c                     | 13 +++++++++++--
>  11 files changed, 96 insertions(+), 39 deletions(-)
>
> diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst
> index 580ab9a0fe31..18ac7d35c145 100644
> --- a/Documentation/filesystems/overlayfs.rst
> +++ b/Documentation/filesystems/overlayfs.rst
> @@ -137,6 +137,29 @@ Only the lists of names from directories are merged.  Other content
>  such as metadata and extended attributes are reported for the upper
>  directory only.  These attributes of the lower directory are hidden.
>
> +credentials
> +-----------
> +
> +By default, all access to the upper, lower and work directories is the
> +recorded mounter's MAC and DAC credentials.  The incoming accesses are
> +checked against the caller's credentials.
> +
> +In the case where caller MAC or DAC credentials do not overlap, a
> +use case available in older versions of the driver, the
> +override_creds mount flag can be turned off and help when the use
> +pattern has caller with legitimate credentials where the mounter
> +does not.  Several unintended side effects will occur though.  The
> +caller without certain key capabilities or lower privilege will not
> +always be able to delete files or directories, create nodes, or
> +search some restricted directories.  The ability to search and read
> +a directory entry is spotty as a result of the cache mechanism not
> +retesting the credentials because of the assumption, a privileged
> +caller can fill cache, then a lower privilege can read the directory
> +cache.  The uneven security model where cache, upperdir and workdir
> +are opened at privilege, but accessed without creating a form of
> +privilege escalation, should only be used with strict understanding
> +of the side effects and of the security policies.
> +

Since your earlier versions, overlayfs.rst grew the section 'Permission model'.
Please work your documentation into that section or at least add it near the
new section and make sure that the content of the two sections do not
contradicts each other.

Thanks,
Amir.

Re: [PATCH v15 0/4] overlayfs override_creds=off & nested get xattr fix

[Amir Goldstein]

On Tue, Nov 5, 2019 at 5:20 PM Mark Salyzyn <salyzyn@android.com> wrote:
>
> On 11/4/19 11:56 PM, Amir Goldstein wrote:
> > On Mon, Nov 4, 2019 at 11:53 PM Mark Salyzyn <salyzyn@android.com> wrote:
> >> Patch series:
> >>
> >> Mark Salyzyn (4):
> >>    Add flags option to get xattr method paired to __vfs_getxattr
> > Sigh.. did not get to fsdevel (again...) I already told you several times
> > that you need to use a shorter CC list.
>
> This is a direct result of the _required_ scripts/get_maintainer.pl
> logic, I am not going to override it for first send. I was going to
> forward to fsdevel after the messages settled, I am still waiting for
> 1/4 to land on lore before continuing.

How do you expect it to land in lore if the mailing list server rejects it?
If I were you, I would *first* post the patch to the small crowd of the
patch set, which includes fsdevel and *then* forward patch 1 to all
maintainers with a link to lore for the series.

The result as is was in your last 15 posting is much worst.
There is a ghost patch in the series that nobody knows where to find.

>
> The first patch in the series needs to get in before the others. I was
> told to send the first one individually because the series has so many
> recipients and stakeholders, and <crickets> because no on could see the
> reason for the patch once it was all by itself. So I rejoined the set so
> they could see the reason for the first patch.
>
> If only the first patch in the series that added the flag argument got
> in (somewhere), then the overlayfs portion would be much easier to handle.
>
> >>    overlayfs: handle XATTR_NOSECURITY flag for get xattr method
> >>    overlayfs: internal getxattr operations without sepolicy checking
> >>    overlayfs: override_creds=off option bypass creator_cred
> > It would be better for review IMO if you rebase your series on top of
> > git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git ovl-unpriv
> Will do, send it only to fsdevel, other recipients? What do I do with
> get_maintainer.pl? The first patch in the series is noisy, I am getting
> more and more uncomfortable sending it to the list as it looks more and
> more like spam.

get_maintainer.pl is a suggestion. common sense should be applied.
Sending the entire series to the crowd of this message seems fine to
me (I also added fsdevel). LKML is quite an overkill IMO and
linux-doc also seems out of context if you ask me.

Thanks,
Amir.

Re: [PATCH v15 0/4] overlayfs override_creds=off & nested get xattr fix

[Mark Salyzyn]

On 11/4/19 11:56 PM, Amir Goldstein wrote:
> On Mon, Nov 4, 2019 at 11:53 PM Mark Salyzyn <salyzyn@android.com> wrote:
>> Patch series:
>>
>> Mark Salyzyn (4):
>>    Add flags option to get xattr method paired to __vfs_getxattr
> Sigh.. did not get to fsdevel (again...) I already told you several times
> that you need to use a shorter CC list.

This is a direct result of the _required_ scripts/get_maintainer.pl 
logic, I am not going to override it for first send. I was going to 
forward to fsdevel after the messages settled, I am still waiting for 
1/4 to land on lore before continuing.

The first patch in the series needs to get in before the others. I was 
told to send the first one individually because the series has so many 
recipients and stakeholders, and <crickets> because no on could see the 
reason for the patch once it was all by itself. So I rejoined the set so 
they could see the reason for the first patch.

If only the first patch in the series that added the flag argument got 
in (somewhere), then the overlayfs portion would be much easier to handle.

>>    overlayfs: handle XATTR_NOSECURITY flag for get xattr method
>>    overlayfs: internal getxattr operations without sepolicy checking
>>    overlayfs: override_creds=off option bypass creator_cred
> It would be better for review IMO if you rebase your series on top of
> git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git ovl-unpriv
Will do, send it only to fsdevel, other recipients? What do I do with 
get_maintainer.pl? The first patch in the series is noisy, I am getting 
more and more uncomfortable sending it to the list as it looks more and 
more like spam.
> 1. internal getxattr patch would be a one liner change to ovl_own_getxattr()
> 2. The documentation of override_creds would be much more
> meaningful if it used the overlay permission model terminology
> that Miklos added in his patch set and extend it
>
> Thanks,
> Amir.

-- Mark

Re: [PATCH v15 0/4] overlayfs override_creds=off & nested get xattr fix

[Amir Goldstein]

On Mon, Nov 4, 2019 at 11:53 PM Mark Salyzyn <salyzyn@android.com> wrote:
>
> Patch series:
>
> Mark Salyzyn (4):
>   Add flags option to get xattr method paired to __vfs_getxattr

Sigh.. did not get to fsdevel (again...) I already told you several times
that you need to use a shorter CC list.

>   overlayfs: handle XATTR_NOSECURITY flag for get xattr method
>   overlayfs: internal getxattr operations without sepolicy checking
>   overlayfs: override_creds=off option bypass creator_cred

It would be better for review IMO if you rebase your series on top of
git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git ovl-unpriv

1. internal getxattr patch would be a one liner change to ovl_own_getxattr()
2. The documentation of override_creds would be much more
meaningful if it used the overlay permission model terminology
that Miklos added in his patch set and extend it

Thanks,
Amir.

[PATCH v15 0/4] overlayfs override_creds=off & nested get xattr fix

[Mark Salyzyn]

Patch series:

Mark Salyzyn (4):
  Add flags option to get xattr method paired to __vfs_getxattr
  overlayfs: handle XATTR_NOSECURITY flag for get xattr method
  overlayfs: internal getxattr operations without sepolicy checking
  overlayfs: override_creds=off option bypass creator_cred

The first three patches address fundamental security issues that should
be solved regardless of the override_creds=off feature.

The fourth adds the feature depends on these other fixes.

By default, all access to the upper, lower and work directories is the
recorded mounter's MAC and DAC credentials.  The incoming accesses are
checked against the caller's credentials.

If the principles of least privilege are applied for sepolicy, the
mounter's credentials might not overlap the credentials of the caller's
when accessing the overlayfs filesystem.  For example, a file that a
lower DAC privileged caller can execute, is MAC denied to the
generally higher DAC privileged mounter, to prevent an attack vector.

We add the option to turn off override_creds in the mount options; all
subsequent operations after mount on the filesystem will be only the
caller's credentials.  The module boolean parameter and mount option
override_creds is also added as a presence check for this "feature",
existence of /sys/module/overlay/parameters/overlay_creds

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

---
v15
- Revert back to v4 with fixes from on the way from v5-v14. The single
  structure argument passing to address the complaints about too many
  arguments was rejected by the community.
- Drop the udner discussion fix for an additional CAP_DAC_READ_SEARCH
  check. Can address that independently.
- ToDo: upstream test frame for thes security fixes (currently testing
  is all in Android).

v14:
- Rejoin, rebase and a few adjustments.

v13:
- Pull out first patch and try to get it in alone feedback, some
  Acks, and then <crickets> because people forgot why we were doing i.

v12:
- Restore squished out patch 2 and 3 in the series,
  then change algorithm to add flags argument.
  Per-thread flag is a large security surface.

v11:
- Squish out v10 introduced patch 2 and 3 in the series,
  then and use per-thread flag instead for nesting.
- Switch name to ovl_do_vds_getxattr for __vds_getxattr wrapper.
- Add sb argument to ovl_revert_creds to match future work.

v10:
- Return NULL on CAP_DAC_READ_SEARCH
- Add __get xattr method to solve sepolicy logging issue
- Drop unnecessary sys_admin sepolicy checking for administrative
  driver internal xattr functions.

v6:
- Drop CONFIG_OVERLAY_FS_OVERRIDE_CREDS.
- Do better with the documentation, drop rationalizations.
- pr_warn message adjusted to report consequences.

v5:
- beefed up the caveats in the Documentation
- Is dependent on
  "overlayfs: check CAP_DAC_READ_SEARCH before issuing exportfs_decode_fh"
  "overlayfs: check CAP_MKNOD before issuing vfs_whiteout"
- Added prwarn when override_creds=off

v4:
- spelling and grammar errors in text

v3:
- Change name from caller_credentials / creator_credentials to the
  boolean override_creds.
- Changed from creator to mounter credentials.
- Updated and fortified the documentation.
- Added CONFIG_OVERLAY_FS_OVERRIDE_CREDS

v2:
- Forward port changed attr to stat, resulting in a build error.
- altered commit message.

 Documentation/filesystems/locking.rst   |  2 +-
 Documentation/filesystems/overlayfs.txt | 23 ++++++++++++++++
 fs/9p/acl.c                             |  3 ++-
 fs/9p/xattr.c                           |  3 ++-
 fs/afs/xattr.c                          | 26 +++++++++---------
 fs/btrfs/xattr.c                        |  3 ++-
 fs/ceph/xattr.c                         |  3 ++-
 fs/cifs/xattr.c                         |  2 +-
 fs/ecryptfs/inode.c                     |  6 +++--
 fs/ecryptfs/mmap.c                      |  2 +-
 fs/erofs/xattr.c                        |  3 ++-
 fs/ext2/xattr_security.c                |  2 +-
 fs/ext2/xattr_trusted.c                 |  2 +-
 fs/ext2/xattr_user.c                    |  2 +-
 fs/ext4/xattr_security.c                |  2 +-
 fs/ext4/xattr_trusted.c                 |  2 +-
 fs/ext4/xattr_user.c                    |  2 +-
 fs/f2fs/xattr.c                         |  4 +--
 fs/fuse/xattr.c                         |  4 +--
 fs/gfs2/xattr.c                         |  3 ++-
 fs/hfs/attr.c                           |  2 +-
 fs/hfsplus/xattr.c                      |  3 ++-
 fs/hfsplus/xattr_security.c             |  3 ++-
 fs/hfsplus/xattr_trusted.c              |  3 ++-
 fs/hfsplus/xattr_user.c                 |  3 ++-
 fs/jffs2/security.c                     |  3 ++-
 fs/jffs2/xattr_trusted.c                |  3 ++-
 fs/jffs2/xattr_user.c                   |  3 ++-
 fs/jfs/xattr.c                          |  5 ++--
 fs/kernfs/inode.c                       |  3 ++-
 fs/nfs/nfs4proc.c                       |  6 +++--
 fs/ocfs2/xattr.c                        |  9 ++++---
 fs/orangefs/xattr.c                     |  3 ++-
 fs/overlayfs/copy_up.c                  |  2 +-
 fs/overlayfs/dir.c                      | 17 +++++++-----
 fs/overlayfs/file.c                     | 20 +++++++-------
 fs/overlayfs/inode.c                    | 23 ++++++++--------
 fs/overlayfs/namei.c                    | 18 +++++++------
 fs/overlayfs/overlayfs.h                | 11 +++++++-
 fs/overlayfs/ovl_entry.h                |  1 +
 fs/overlayfs/readdir.c                  |  4 +--
 fs/overlayfs/super.c                    | 34 ++++++++++++++++++-----
 fs/overlayfs/util.c                     | 30 +++++++++++++--------
 fs/posix_acl.c                          |  2 +-
 fs/reiserfs/xattr_security.c            |  3 ++-
 fs/reiserfs/xattr_trusted.c             |  3 ++-
 fs/reiserfs/xattr_user.c                |  3 ++-
 fs/squashfs/xattr.c                     |  2 +-
 fs/ubifs/xattr.c                        |  3 ++-
 fs/xattr.c                              | 36 ++++++++++++-------------
 fs/xfs/xfs_xattr.c                      |  3 ++-
 include/linux/xattr.h                   |  9 ++++---
 include/uapi/linux/xattr.h              |  7 +++--
 mm/shmem.c                              |  3 ++-
 net/socket.c                            |  3 ++-
 security/commoncap.c                    |  6 +++--
 security/integrity/evm/evm_main.c       |  3 ++-
 security/selinux/hooks.c                | 11 +++++---
 security/smack/smack_lsm.c              |  5 ++--
 59 files changed, 261 insertions(+), 149 deletions(-)

-- 
2.24.0.rc1.363.gb1bccd3e3d-goog