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[PATCH v24 05/22] vfs: Add permission flags for setting file attributes

From Andreas Gruenbacher <agruenba@redhat.com>
Newsgroups linux.kernel
Subject [PATCH v24 05/22] vfs: Add permission flags for setting file attributes
Date 2016-07-25 16:20 +0200
Message-ID <rYOTF-5Bn-49@gated-at.bofh.it> (permalink)
References <rYOJY-5xo-27@gated-at.bofh.it>
Organization linux.* mail to news gateway

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Richacls support permissions that allow to take ownership of a file,
change the file permissions, and set the file timestamps.  Support that
by introducing new permission mask flags and by checking for those mask
flags in inode_change_ok().

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
Reviewed-by: Steve French <steve.french@primarydata.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
---
 fs/attr.c          | 79 +++++++++++++++++++++++++++++++++++++++++++++---------
 include/linux/fs.h |  3 +++
 2 files changed, 70 insertions(+), 12 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index 7ca7fa0..2a8c49c 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -17,6 +17,65 @@
 #include <linux/ima.h>
 
 /**
+ * inode_extended_permission  -  permissions beyond read/write/execute
+ *
+ * Check for permissions that only richacls can currently grant.
+ */
+static int inode_extended_permission(struct inode *inode, int mask)
+{
+	if (!IS_RICHACL(inode))
+		return -EPERM;
+	return inode_permission(inode, mask);
+}
+
+static bool inode_uid_change_ok(struct inode *inode, kuid_t ia_uid)
+{
+	if (uid_eq(current_fsuid(), inode->i_uid) &&
+	    uid_eq(ia_uid, inode->i_uid))
+		return true;
+	if (uid_eq(current_fsuid(), ia_uid) &&
+	    inode_extended_permission(inode, MAY_TAKE_OWNERSHIP) == 0)
+		return true;
+	if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
+		return true;
+	return false;
+}
+
+static bool inode_gid_change_ok(struct inode *inode, kgid_t ia_gid)
+{
+	int in_group = in_group_p(ia_gid);
+	if (uid_eq(current_fsuid(), inode->i_uid) &&
+	    (in_group || gid_eq(ia_gid, inode->i_gid)))
+		return true;
+	if (in_group && inode_extended_permission(inode, MAY_TAKE_OWNERSHIP) == 0)
+		return true;
+	if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
+		return true;
+	return false;
+}
+
+/**
+ * inode_owner_permitted_or_capable
+ *
+ * Check for permissions implicitly granted to the owner, like MAY_CHMOD or
+ * MAY_SET_TIMES.  Equivalent to inode_owner_or_capable for file systems
+ * without support for those permissions.
+ */
+static bool inode_owner_permitted_or_capable(struct inode *inode, int mask)
+{
+	struct user_namespace *ns;
+
+	if (uid_eq(current_fsuid(), inode->i_uid))
+		return true;
+	if (inode_extended_permission(inode, mask) == 0)
+		return true;
+	ns = current_user_ns();
+	if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
+		return true;
+	return false;
+}
+
+/**
  * inode_change_ok - check if attribute changes to an inode are allowed
  * @inode:	inode to check
  * @attr:	attributes to change
@@ -47,22 +106,18 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)
 		return 0;
 
 	/* Make sure a caller can chown. */
-	if ((ia_valid & ATTR_UID) &&
-	    (!uid_eq(current_fsuid(), inode->i_uid) ||
-	     !uid_eq(attr->ia_uid, inode->i_uid)) &&
-	    !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
-		return -EPERM;
+	if (ia_valid & ATTR_UID)
+		if (!inode_uid_change_ok(inode, attr->ia_uid))
+			return -EPERM;
 
 	/* Make sure caller can chgrp. */
-	if ((ia_valid & ATTR_GID) &&
-	    (!uid_eq(current_fsuid(), inode->i_uid) ||
-	    (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
-	    !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
-		return -EPERM;
+	if (ia_valid & ATTR_GID)
+		if (!inode_gid_change_ok(inode, attr->ia_gid))
+			return -EPERM;
 
 	/* Make sure a caller can chmod. */
 	if (ia_valid & ATTR_MODE) {
-		if (!inode_owner_or_capable(inode))
+		if (!inode_owner_permitted_or_capable(inode, MAY_CHMOD))
 			return -EPERM;
 		/* Also check the setgid bit! */
 		if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
@@ -73,7 +128,7 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)
 
 	/* Check for setting the inode time. */
 	if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
-		if (!inode_owner_or_capable(inode))
+		if (!inode_owner_permitted_or_capable(inode, MAY_SET_TIMES))
 			return -EPERM;
 	}
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 208f73b..bb36561 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -88,6 +88,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 #define MAY_CREATE_DIR		0x00000200
 #define MAY_DELETE_CHILD	0x00000400
 #define MAY_DELETE_SELF		0x00000800
+#define MAY_TAKE_OWNERSHIP	0x00001000
+#define MAY_CHMOD		0x00002000
+#define MAY_SET_TIMES		0x00004000
 
 /*
  * flags in file.f_mode.  Note that FMODE_READ and FMODE_WRITE must correspond
-- 
2.5.5

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Thread

[PATCH v24 00/22] Richacls (Core and Ext4) Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:10 +0200
  [PATCH v24 03/22] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 21/22] ext4: Add richacl support Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 22/22] ext4: Add richacl feature flag Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 13/22] richacl: Update the file masks in chmod() Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 18/22] richacl: Add richacl xattr handler Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 19/22] vfs: Add richacl permission checking Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 09/22] richacl: Compute maximum file masks from an acl Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 01/22] vfs: Add IS_ACL() and IS_RICHACL() tests Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 20/22] vfs: Move check_posix_acl and check_richacl out of fs/namei.c Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 04/22] vfs: Make the inode passed to inode_change_ok non-const Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 06/22] richacl: In-memory representation and helper functions Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 02/22] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 15/22] richacl: Create-time inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 17/22] richacl: xattr mapping functions Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 11/22] vfs: Add get_richacl and set_richacl inode operations Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 12/22] vfs: Cache richacl in struct inode Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 05/22] vfs: Add permission flags for setting file attributes Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 08/22] richacl: Permission check algorithm Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 14/22] richacl: Check if an acl is equivalent to a file mode Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 07/22] richacl: Permission mapping functions Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 10/22] vfs: Cache base_acl objects in inodes Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200
  [PATCH v24 16/22] richacl: Automatic Inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2016-07-25 16:20 +0200

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