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[RFC v6 09/40] richacl: Update the file masks in chmod()

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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>
---
 fs/richacl_base.c       | 40 ++++++++++++++++++++++++++++++++++++++++
 include/linux/richacl.h |  1 +
 2 files changed, 41 insertions(+)

diff --git a/fs/richacl_base.c b/fs/richacl_base.c
index 8426600..fd81158 100644
--- a/fs/richacl_base.c
+++ b/fs/richacl_base.c
@@ -338,3 +338,43 @@ restart:
 	acl->a_flags &= ~(RICHACL_WRITE_THROUGH | RICHACL_MASKED);
 }
 EXPORT_SYMBOL_GPL(richacl_compute_max_masks);
+
+/**
+ * richacl_chmod  -  update the file masks to reflect the new mode
+ * @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+ * Return a copy of @acl where the file masks have been replaced by the file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.
+ */
+struct richacl *
+richacl_chmod(struct richacl *acl, mode_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))
+		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;
+}
+EXPORT_SYMBOL_GPL(richacl_chmod);
diff --git a/include/linux/richacl.h b/include/linux/richacl.h
index 3d719db..8df6d93 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -304,5 +304,6 @@ extern int richacl_masks_to_mode(const struct richacl *);
 extern unsigned int richacl_mode_to_mask(mode_t);
 extern unsigned int richacl_want_to_mask(unsigned int);
 extern void richacl_compute_max_masks(struct richacl *, kuid_t);
+extern struct richacl *richacl_chmod(struct richacl *, mode_t);
 
 #endif /* __RICHACL_H */
-- 
2.5.0

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[RFC v6 00/40] Richacls Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:00 +0200
  [RFC v6 25/40] richacl: Isolate the owner and group classes Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:00 +0200
  [RFC v6 33/40] richacl: Add support for unmapped identifiers Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:00 +0200
  [RFC v6 39/40] nfs: Add richacl support Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:00 +0200
  [RFC v6 29/40] nfsd: Use richacls as internal acl representation Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:00 +0200
  [RFC v6 23/40] richacl: Set the owner permissions to the owner mask Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 21/40] richacl: Move everyone@ aces down the acl Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 31/40] nfsd: Add support for the v4.1 dacl attribute Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 14/40] richacl: Create-time inheritance Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 19/40] ext4: Add richacl feature flag Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 28/40] nfsd: Keep list of acls to dispose of in compoundargs Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 26/40] richacl: Apply the file masks to a richacl Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 20/40] richacl: acl editing helper functions Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 15/40] richacl: Automatic Inheritance Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 22/40] richacl: Propagate everyone@ permissions to other aces Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 24/40] richacl: Set the other permissions to the other mask Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 18/40] ext4: Add richacl support Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 11/40] vfs: Cache base_acl objects in inodes Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 12/40] vfs: Cache richacl in struct inode Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 17/40] vfs: Add richacl permission checking Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 27/40] richacl: Create richacl from mode values Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:10 +0200
  [RFC v6 01/40] vfs: Add IS_ACL() and IS_RICHACL() tests Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:20 +0200
  [RFC v6 07/40] richacl: Permission mapping functions Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:20 +0200
  [RFC v6 05/40] vfs: Add permission flags for setting file attributes Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:20 +0200
  [RFC v6 04/40] vfs: Make the inode passed to inode_change_ok non-const Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:20 +0200
  [RFC v6 02/40] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:20 +0200
  [RFC v6 09/40] richacl: Update the file masks in chmod() Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-08-04 14:20 +0200

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