[PATCH v20 15/23] richacl: Update the file masks in chmod()

From	Andreas Gruenbacher <agruenba@redhat.com>
Newsgroups	linux.kernel
Subject	[PATCH v20 15/23] richacl: Update the file masks in chmod()
Date	2016-03-16 23:30 +0100
Message-ID	<rds72-6Wr-65@gated-at.bofh.it> (permalink)
References	<rdrXj-6Sv-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Doing a chmod() sets the file mode, which includes the file permission
bits.  When a file has a richacl, the permissions that the richacl
grants need to be limited to what the new file permission bits allow.

This is done by setting the file masks in the richacl to what the file
permission bits map to.  The richacl access check algorithm takes the
file masks into account, which ensures that the richacl cannot grant too
many permissions.

It is possible to explicitly add permissions to the file masks which go
beyond what the file permission bits can grant (like the
RICHACE_WRITE_ACL permission).  The POSIX.1 standard calls this an
alternate file access control mechanism.  A subsequent chmod() would
ensure that those permissions are disabled again.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/richacl.c            | 71 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/richacl.h |  1 +
 2 files changed, 72 insertions(+)

diff --git a/fs/richacl.c b/fs/richacl.c
index 59ef600..23c1aa9 100644
--- a/fs/richacl.c
+++ b/fs/richacl.c
@@ -543,3 +543,74 @@ out:
 	return denied ? -EACCES : 0;
 }
 EXPORT_SYMBOL_GPL(richacl_permission);
+
+/**
+ * __richacl_chmod  -  update the file masks to reflect the new mode
+ * @acl:	access control list
+ * @mode:	new file permission bits including the file type
+ *
+ * Return a copy of @acl where the file masks have been replaced by the file
+ * masks corresponding to the file permission bits in @mode, or returns @acl
+ * itself if the file masks are already up to date.  Takes over a reference
+ * to @acl.
+ */
+static struct richacl *
+__richacl_chmod(struct richacl *acl, umode_t mode)
+{
+	unsigned int x = S_ISDIR(mode) ? 0 : RICHACE_DELETE_CHILD;
+	unsigned int owner_mask, group_mask, other_mask;
+	struct richacl *clone;
+
+	owner_mask = richacl_mode_to_mask(mode >> 6) & ~x;
+	group_mask = richacl_mode_to_mask(mode >> 3) & ~x;
+	other_mask = richacl_mode_to_mask(mode)      & ~x;
+
+	if (acl->a_owner_mask == owner_mask &&
+	    acl->a_group_mask == group_mask &&
+	    acl->a_other_mask == other_mask &&
+	    (acl->a_flags & RICHACL_MASKED) &&
+	    (acl->a_flags & RICHACL_WRITE_THROUGH))
+		return acl;
+
+	clone = richacl_clone(acl, GFP_KERNEL);
+	richacl_put(acl);
+	if (!clone)
+		return ERR_PTR(-ENOMEM);
+
+	clone->a_flags |= (RICHACL_WRITE_THROUGH | RICHACL_MASKED);
+	clone->a_owner_mask = owner_mask;
+	clone->a_group_mask = group_mask;
+	clone->a_other_mask = other_mask;
+
+	return clone;
+}
+
+/**
+ * richacl_chmod  -  filesystem chmod helper
+ * @inode:	inode whose file permission bits to change
+ * @mode:	new file permission bits including the file type
+ *
+ * Helper for filesystems to use to perform a chmod on the richacl of an inode.
+ */
+int
+richacl_chmod(struct inode *inode, umode_t mode)
+{
+	struct richacl *acl;
+	int retval;
+
+	if (S_ISLNK(mode))
+		return -EOPNOTSUPP;
+	if (!inode->i_op->set_richacl)
+		return -EOPNOTSUPP;
+	acl = get_richacl(inode);
+	if (IS_ERR_OR_NULL(acl))
+		return PTR_ERR(acl);
+	acl = __richacl_chmod(acl, mode);
+	if (IS_ERR(acl))
+		return PTR_ERR(acl);
+	retval = inode->i_op->set_richacl(inode, acl);
+	richacl_put(acl);
+
+	return retval;
+}
+EXPORT_SYMBOL(richacl_chmod);
diff --git a/include/linux/richacl.h b/include/linux/richacl.h
index d19b61b..554f050 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -185,5 +185,6 @@ extern unsigned int richacl_mode_to_mask(umode_t);
 extern unsigned int richacl_want_to_mask(unsigned int);
 extern void richacl_compute_max_masks(struct richacl *);
 extern int richacl_permission(struct inode *, const struct richacl *, int);
+extern int richacl_chmod(struct inode *, umode_t);
 
 #endif /* __RICHACL_H */
-- 
2.5.0

Thread

[PATCH v20 00/23] Richacls (Core and Ext4) Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:20 +0100
  [PATCH v20 03/23] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:20 +0100
  [PATCH v20 01/23] vfs: Add IS_ACL() and IS_RICHACL() tests Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:20 +0100
  [PATCH v20 11/23] posix_acl: Improve xattr fixup code Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 13/23] vfs: Add get_richacl and set_richacl inode operations Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 05/23] vfs: Add permission flags for setting file attributes Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 09/23] richacl: Permission check algorithm Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 14/23] vfs: Cache richacl in struct inode Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 23/23] ext4: Add richacl feature flag Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 10/23] posix_acl: Unexport acl_by_type and make it static Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 04/23] vfs: Make the inode passed to inode_change_ok non-const Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 02/23] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 22/23] ext4: Add richacl support Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 08/23] richacl: Compute maximum file masks from an acl Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 16/23] richacl: Check if an acl is equivalent to a file mode Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 19/23] richacl: xattr mapping functions Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 06/23] richacl: In-memory representation and helper functions Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 21/23] vfs: Add richacl permission checking Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 07/23] richacl: Permission mapping functions Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 12/23] vfs: Cache base_acl objects in inodes Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 20/23] richacl: Add richacl xattr handler Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 18/23] richacl: Automatic Inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 15/23] richacl: Update the file masks in chmod() Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100
  [PATCH v20 17/23] richacl: Create-time inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2016-03-16 23:30 +0100

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