linux-kernel - [PATCH 4/7] selinux: Implementation for inode_copy_up

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Date:	Fri,  8 Jul 2016 12:19:39 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	miklos@...redi.hu, sds@...ho.nsa.gov, pmoore@...hat.com,
	casey@...aufler-ca.com, linux-kernel@...r.kernel.org,
	linux-unionfs@...r.kernel.org,
	linux-security-module@...r.kernel.org
Cc:	dwalsh@...hat.com, dhowells@...hat.com, viro@...IV.linux.org.uk,
	vgoyal@...hat.com, linux-fsdevel@...r.kernel.org
Subject: [PATCH 4/7] 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@...hat.com>
---
 security/selinux/hooks.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index c82ee54..4fda548 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3290,6 +3290,21 @@ 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)
@@ -6077,6 +6092,7 @@ 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),
-- 
2.7.4