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[PATCH v28 12/21] 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>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
Acked-by: Jeff Layton <jlayton@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 731c468..a199245 100644
--- a/fs/richacl.c
+++ b/fs/richacl.c
@@ -541,3 +541,74 @@ void richacl_compute_max_masks(struct richacl *acl)
 	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
+ * @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+ * Return a copy of @acl where the file masks have been replaced by the file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 207fe06..3cd5e53 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -189,5 +189,6 @@ extern int richacl_masks_to_mode(const struct richacl *);
 extern unsigned int richacl_mode_to_mask(umode_t);
 extern int richacl_permission(struct inode *, const struct richacl *, int);
 extern void richacl_compute_max_masks(struct richacl *);
+extern int richacl_chmod(struct inode *, umode_t);
 
 #endif /* __RICHACL_H */
-- 
2.7.4

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[PATCH v28 00/21] Richacls (Core and Ext4) Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 19/21] vfs: Move check_posix_acl and check_richacl out of fs/namei.c Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 01/21] vfs: Add IS_ACL() and IS_RICHACL() tests Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 03/21] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 16/21] richacl: xattr mapping functions Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 15/21] richacl: Automatic Inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 08/21] richacl: Compute maximum file masks from an acl Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 21/21] ext4: Add richacl feature flag Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 20/21] ext4: Add richacl support Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:40 +0100
  [PATCH v28 06/21] richacl: Permission mapping functions Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100
  [PATCH v28 02/21] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100
  [PATCH v28 11/21] vfs: Cache richacl in struct inode Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100
  [PATCH v28 14/21] richacl: Create-time inheritance Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100
  [PATCH v28 04/21] vfs: Add permission flags for setting file attributes Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100
  [PATCH v28 12/21] richacl: Update the file masks in chmod() Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100
  [PATCH v28 07/21] richacl: Permission check algorithm Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100
  [PATCH v28 05/21] richacl: In-memory representation and helper functions Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100
  [PATCH v28 10/21] vfs: Add get_richacl and set_richacl inode operations Andreas Gruenbacher <agruenba@redhat.com> - 2017-02-13 16:50 +0100

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