[PATCH AUTOSEL for 4.4 099/167] ovl: filter trusted xattr for non-admin

Sasha Levin
2018-03-19T16:10:14Z

From: Miklos Szeredi <mszeredi@redhat.com>

[ Upstream commit a082c6f680da298cf075886ff032f32ccb7c5e1a ]

Filesystems filter out extended attributes in the "trusted." domain for
unprivlieged callers.

Overlay calls underlying filesystem's method with elevated privs, so need
to do the filtering in overlayfs too.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
fs/overlayfs/inode.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 220b04f04523..985a4cdae06d 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -272,6 +272,16 @@ ssize_t ovl_getxattr(struct dentry *dentry, const char *name,
return vfs_getxattr(realpath.dentry, name, value, size);
}

+static bool ovl_can_list(const char *s)
+{
+ /* List all non-trusted xatts */
+ if (strncmp(s, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) != 0)
+ return true;
+
+ /* Never list trusted.overlay, list other trusted for superuser only */
+ return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
+}
+
ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
{
struct path realpath;
@@ -296,7 +306,7 @@ ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
return -EIO;

len -= slen;
- if (ovl_is_private_xattr(s)) {
+ if (!ovl_can_list(s)) {
res -= slen;
memmove(s, s + slen, len);
} else {
--
2.14.1