selinux: Implementation for inode_copy_up_xattr() hook

When a file is copied up in overlay, we have already created file on
upper/ with right label and there is no need to copy up selinux
label/xattr from lower file to upper file. In fact in case of context
mount, we don't want to copy up label as newly created file got its label
from context= option.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 40597ed00ba9..a2d510895ff3 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3313,6 +3313,21 @@ static int selinux_inode_copy_up(struct dentry *src, struct cred **new)
         return 0;
 }
 
+static int selinux_inode_copy_up_xattr(const char *name)
+{
+        /* The copy_up hook above sets the initial context on an inode, but we
+         * don't then want to overwrite it by blindly copying all the lower
+         * xattrs up.  Instead, we have to filter out SELinux-related xattrs.
+         */
+        if (strcmp(name, XATTR_NAME_SELINUX) == 0)
+                return 1; /* Discard */
+        /*
+         * Any other attribute apart from SELINUX is not claimed, supported
+         * by selinux.
+         */
+        return -EOPNOTSUPP;
+}
+
 /* file security operations */
 
 static int selinux_revalidate_file_permission(struct file *file, int mask)
@@ -6109,6 +6124,7 @@ static struct security_hook_list selinux_hooks[] = {
         LSM_HOOK_INIT(inode_listsecurity, selinux_inode_listsecurity),
         LSM_HOOK_INIT(inode_getsecid, selinux_inode_getsecid),
         LSM_HOOK_INIT(inode_copy_up, selinux_inode_copy_up),
+        LSM_HOOK_INIT(inode_copy_up_xattr, selinux_inode_copy_up_xattr),
 
         LSM_HOOK_INIT(file_permission, selinux_file_permission),
         LSM_HOOK_INIT(file_alloc_security, selinux_file_alloc_security),