richacl: Create-time inheritance

When a new file is created, it can inherit an acl from its parent
directory; this is similar to how default acls work in POSIX (draft)
ACLs.

As with POSIX ACLs, if a file inherits an acl from its parent directory,
the intersection between the create mode and the permissions granted by
the inherited acl determines the file masks and file permission bits,
and the umask is ignored.

Acked-by: J. Bruce Fields <[email protected]>
Acked-by: David Howells <[email protected]>
Signed-off-by: Andreas Gruenbacher <[email protected]>
Signed-off-by: Aneesh Kumar K.V <[email protected]>

fs/Makefile

@@ -49,7 +49,7 @@ obj-$(CONFIG_GENERIC_ACL)	+= generic_acl.o
 
 obj-$(CONFIG_FHANDLE)		+= fhandle.o
 obj-$(CONFIG_FS_RICHACL)	+= richacl.o
-richacl-y			:= richacl_base.o
+richacl-y			:= richacl_base.o richacl_inode.o
 
 obj-y				+= quota/
 

fs/richacl_base.c

@@ -451,3 +451,72 @@ richacl_permission(struct inode *inode, const struct richacl *acl,
 	return denied ? -EACCES : 0;
 }
 EXPORT_SYMBOL_GPL(richacl_permission);
+
+/**
+ * richacl_inherit  -  compute the inherited acl of a new file
+ * @dir_acl:	acl of the containing directory
+ * @isdir:	inherit by a directory or non-directory?
+ *
+ * A directory can have acl entries which files and/or directories created
+ * inside the directory will inherit.  This function computes the acl for such
+ * a new file.  If there is no inheritable acl, it will return %NULL.
+ */
+struct richacl *
+richacl_inherit(const struct richacl *dir_acl, int isdir)
+{
+	const struct richace *dir_ace;
+	struct richacl *acl = NULL;
+	struct richace *ace;
+	int count = 0;
+
+	if (isdir) {
+		richacl_for_each_entry(dir_ace, dir_acl) {
+			if (!richace_is_inheritable(dir_ace))
+				continue;
+			count++;
+		}
+		if (!count)
+			return NULL;
+		acl = richacl_alloc(count);
+		if (!acl)
+			return ERR_PTR(-ENOMEM);
+		ace = acl->a_entries;
+		richacl_for_each_entry(dir_ace, dir_acl) {
+			if (!richace_is_inheritable(dir_ace))
+				continue;
+			memcpy(ace, dir_ace, sizeof(struct richace));
+			if (dir_ace->e_flags & ACE4_NO_PROPAGATE_INHERIT_ACE)
+				richace_clear_inheritance_flags(ace);
+			if ((dir_ace->e_flags & ACE4_FILE_INHERIT_ACE) &&
+			    !(dir_ace->e_flags & ACE4_DIRECTORY_INHERIT_ACE))
+				ace->e_flags |= ACE4_INHERIT_ONLY_ACE;
+			ace++;
+		}
+	} else {
+		richacl_for_each_entry(dir_ace, dir_acl) {
+			if (!(dir_ace->e_flags & ACE4_FILE_INHERIT_ACE))
+				continue;
+			count++;
+		}
+		if (!count)
+			return NULL;
+		acl = richacl_alloc(count);
+		if (!acl)
+			return ERR_PTR(-ENOMEM);
+		ace = acl->a_entries;
+		richacl_for_each_entry(dir_ace, dir_acl) {
+			if (!(dir_ace->e_flags & ACE4_FILE_INHERIT_ACE))
+				continue;
+			memcpy(ace, dir_ace, sizeof(struct richace));
+			richace_clear_inheritance_flags(ace);
+			/*
+			 * ACE4_DELETE_CHILD is meaningless for
+			 * non-directories, so clear it.
+			 */
+			ace->e_mask &= ~ACE4_DELETE_CHILD;
+			ace++;
+		}
+	}
+
+	return acl;
+}

fs/richacl_inode.c

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2010  Novell, Inc.
+ * Written by Andreas Gruenbacher <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2, or (at your option) any
+ * later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/richacl.h>
+
+/**
+ * richacl_inherit_inode  -  compute inherited acl and file mode
+ * @dir_acl:	acl of the containing directory
+ * @inode:	inode of the new file (create mode in i_mode)
+ *
+ * The file permission bits in inode->i_mode must be set to the create mode.
+ * If there is an inheritable acl, the maximum permissions that the acl grants
+ * will be computed and permissions not granted by the acl will be removed from
+ * inode->i_mode.  If there is no inheritable acl, the umask will be applied
+ * instead.
+ */
+struct richacl *
+richacl_inherit_inode(const struct richacl *dir_acl, struct inode *inode)
+{
+	struct richacl *acl;
+	mode_t mask;
+
+	acl = richacl_inherit(dir_acl, S_ISDIR(inode->i_mode));
+	if (acl) {
+
+		richacl_compute_max_masks(acl);
+
+		/*
+		 * Ensure that the acl will not grant any permissions beyond
+		 * the create mode.
+		 */
+		acl->a_flags |= ACL4_MASKED;
+		acl->a_owner_mask &= richacl_mode_to_mask(inode->i_mode >> 6) |
+				     ACE4_POSIX_OWNER_ALLOWED;
+		acl->a_group_mask &= richacl_mode_to_mask(inode->i_mode >> 3);
+		acl->a_other_mask &= richacl_mode_to_mask(inode->i_mode);
+		mask = ~S_IRWXUGO | richacl_masks_to_mode(acl);
+	} else
+		mask = ~current_umask();
+
+	inode->i_mode &= mask;
+	return acl;
+}
+EXPORT_SYMBOL_GPL(richacl_inherit_inode);

include/linux/richacl.h

@@ -284,5 +284,9 @@ extern void richacl_compute_max_masks(struct richacl *);
 extern struct richacl *richacl_chmod(struct richacl *, mode_t);
 extern int richacl_permission(struct inode *, const struct richacl *,
 			      unsigned int);
+extern struct richacl *richacl_inherit(const struct richacl *, int);
 
+/* richacl_inode.c */
+extern struct richacl *richacl_inherit_inode(const struct richacl *,
+					     struct inode *);
 #endif /* __RICHACL_H */