[Cluster-devel] [PATCH v13 4/5] overlayfs: internal getxattr operations without sepolicy checking
Mark Salyzyn
salyzyn at android.com
Wed Jul 31 16:57:59 UTC 2019
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 at android.com>
Cc: Miklos Szeredi <miklos at szeredi.hu>
Cc: Jonathan Corbet <corbet at lwn.net>
Cc: Vivek Goyal <vgoyal at redhat.com>
Cc: Eric W. Biederman <ebiederm at xmission.com>
Cc: Amir Goldstein <amir73il at gmail.com>
Cc: Randy Dunlap <rdunlap at infradead.org>
Cc: Stephen Smalley <sds at tycho.nsa.gov>
Cc: linux-unionfs at vger.kernel.org
Cc: linux-doc at vger.kernel.org
Cc: linux-kernel at vger.kernel.org
Cc: kernel-team at android.com
Cc: Eric Van Hensbergen <ericvh at gmail.com>
Cc: Latchesar Ionkov <lucho at ionkov.net>
Cc: Dominique Martinet <asmadeus at codewreck.org>
Cc: David Howells <dhowells at redhat.com>
Cc: Chris Mason <clm at fb.com>
Cc: Josef Bacik <josef at toxicpanda.com>
Cc: David Sterba <dsterba at suse.com>
Cc: Jeff Layton <jlayton at kernel.org>
Cc: Sage Weil <sage at redhat.com>
Cc: Ilya Dryomov <idryomov at gmail.com>
Cc: Steve French <sfrench at samba.org>
Cc: Tyler Hicks <tyhicks at canonical.com>
Cc: Jan Kara <jack at suse.com>
Cc: Theodore Ts'o <tytso at mit.edu>
Cc: Andreas Dilger <adilger.kernel at dilger.ca>
Cc: Jaegeuk Kim <jaegeuk at kernel.org>
Cc: Chao Yu <yuchao0 at huawei.com>
Cc: Bob Peterson <rpeterso at redhat.com>
Cc: Andreas Gruenbacher <agruenba at redhat.com>
Cc: David Woodhouse <dwmw2 at infradead.org>
Cc: Richard Weinberger <richard at nod.at>
Cc: Dave Kleikamp <shaggy at kernel.org>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Tejun Heo <tj at kernel.org>
Cc: Trond Myklebust <trond.myklebust at hammerspace.com>
Cc: Anna Schumaker <anna.schumaker at netapp.com>
Cc: Mark Fasheh <mark at fasheh.com>
Cc: Joel Becker <jlbec at evilplan.org>
Cc: Joseph Qi <joseph.qi at linux.alibaba.com>
Cc: Mike Marshall <hubcap at omnibond.com>
Cc: Martin Brandenburg <martin at omnibond.com>
Cc: Alexander Viro <viro at zeniv.linux.org.uk>
Cc: Phillip Lougher <phillip at squashfs.org.uk>
Cc: Darrick J. Wong <darrick.wong at oracle.com>
Cc: linux-xfs at vger.kernel.org
Cc: Hugh Dickins <hughd at google.com>
Cc: David S. Miller <davem at davemloft.net>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Mathieu Malaterre <malat at debian.org>
Cc: Ernesto A. Fernández <ernesto.mnd.fernandez at gmail.com>
Cc: Vyacheslav Dubeyko <slava at dubeyko.com>
Cc: v9fs-developer at lists.sourceforge.net
Cc: linux-afs at lists.infradead.org
Cc: linux-btrfs at vger.kernel.org
Cc: ceph-devel at vger.kernel.org
Cc: linux-cifs at vger.kernel.org
Cc: samba-technical at lists.samba.org
Cc: ecryptfs at vger.kernel.org
Cc: linux-ext4 at vger.kernel.org
Cc: linux-f2fs-devel at lists.sourceforge.net
Cc: linux-fsdevel at vger.kernel.org
Cc: cluster-devel at redhat.com
Cc: linux-mtd at lists.infradead.org
Cc: jfs-discussion at lists.sourceforge.net
Cc: linux-nfs at vger.kernel.org
Cc: ocfs2-devel at oss.oracle.com
Cc: devel at lists.orangefs.org
Cc: reiserfs-devel at vger.kernel.org
Cc: linux-mm at kvack.org
Cc: netdev at vger.kernel.org
Cc: linux-security-module at vger.kernel.org
Cc: stable at vger.kernel.org # 4.4, 4.9, 4.14 & 4.19
---
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
---
fs/overlayfs/namei.c | 12 +++++++-----
fs/overlayfs/overlayfs.h | 2 ++
fs/overlayfs/util.c | 25 ++++++++++++++++---------
3 files changed, 25 insertions(+), 14 deletions(-)
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 9702f0d5309d..a4a452c489fa 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -106,10 +106,11 @@ int ovl_check_fh_len(struct ovl_fh *fh, int fh_len)
static struct ovl_fh *ovl_get_fh(struct dentry *dentry, const char *name)
{
- int res, err;
+ ssize_t res;
+ int err;
struct ovl_fh *fh = NULL;
- res = vfs_getxattr(dentry, name, NULL, 0);
+ res = ovl_do_vfs_getxattr(dentry, name, NULL, 0);
if (res < 0) {
if (res == -ENODATA || res == -EOPNOTSUPP)
return NULL;
@@ -123,7 +124,7 @@ static struct ovl_fh *ovl_get_fh(struct dentry *dentry, const char *name)
if (!fh)
return ERR_PTR(-ENOMEM);
- res = vfs_getxattr(dentry, name, fh, res);
+ res = ovl_do_vfs_getxattr(dentry, name, fh, res);
if (res < 0)
goto fail;
@@ -141,10 +142,11 @@ static struct ovl_fh *ovl_get_fh(struct dentry *dentry, const char *name)
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 ab3d031c422b..9d26d8758513 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -205,6 +205,8 @@ 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);
+ssize_t ovl_do_vfs_getxattr(struct dentry *dentry, const char *name, void *buf,
+ size_t size);
struct super_block *ovl_same_sb(struct super_block *sb);
int ovl_can_decode_fh(struct super_block *sb);
struct dentry *ovl_indexdir(struct super_block *sb);
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index f5678a3f8350..c588c0d66d8c 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -40,6 +40,13 @@ const struct cred *ovl_override_creds(struct super_block *sb)
return override_creds(ofs->creator_cred);
}
+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,
+ XATTR_NOSECURITY);
+}
+
struct super_block *ovl_same_sb(struct super_block *sb)
{
struct ovl_fs *ofs = sb->s_fs_info;
@@ -537,9 +544,9 @@ 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)
@@ -550,13 +557,13 @@ 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;
@@ -837,13 +844,13 @@ 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 dentry *dentry)
{
- int res;
+ ssize_t res;
/* Only regular files can have metacopy xattr */
if (!S_ISREG(d_inode(dentry)->i_mode))
return 0;
- res = vfs_getxattr(dentry, OVL_XATTR_METACOPY, NULL, 0);
+ res = ovl_do_vfs_getxattr(dentry, OVL_XATTR_METACOPY, NULL, 0);
if (res < 0) {
if (res == -ENODATA || res == -EOPNOTSUPP)
return 0;
@@ -852,7 +859,7 @@ int ovl_check_metacopy_xattr(struct dentry *dentry)
return 1;
out:
- pr_warn_ratelimited("overlayfs: failed to get metacopy (%i)\n", res);
+ pr_warn_ratelimited("overlayfs: failed to get metacopy (%zi)\n", res);
return res;
}
@@ -878,7 +885,7 @@ ssize_t ovl_getxattr(struct dentry *dentry, char *name, char **value,
ssize_t res;
char *buf = NULL;
- res = vfs_getxattr(dentry, name, NULL, 0);
+ res = ovl_do_vfs_getxattr(dentry, name, NULL, 0);
if (res < 0) {
if (res == -ENODATA || res == -EOPNOTSUPP)
return -ENODATA;
@@ -890,7 +897,7 @@ ssize_t ovl_getxattr(struct dentry *dentry, char *name, char **value,
if (!buf)
return -ENOMEM;
- res = vfs_getxattr(dentry, name, buf, res);
+ res = ovl_do_vfs_getxattr(dentry, name, buf, res);
if (res < 0)
goto fail;
}
--
2.22.0.770.g0f2c4a37fd-goog
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