[PATCH v5 09/39] richacl: Update the file masks in chmod()

From	Andreas Gruenbacher <andreas.gruenbacher@gmail.com>
Newsgroups	linux.kernel
Subject	[PATCH v5 09/39] richacl: Update the file masks in chmod()
Date	2015-07-22 15:30 +0200
Message-ID	<pP2fV-85a-41@gated-at.bofh.it> (permalink)
References	<pP1Wx-7Id-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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From: Andreas Gruenbacher <agruenba@redhat.com>

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 23e9824..e88cdda 100644
--- a/fs/richacl_base.c
+++ b/fs/richacl_base.c
@@ -334,3 +334,43 @@ restart:
 	acl->a_flags &= ~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+ * Return a copy of @acl where the file masks have been replaced by the file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_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 90baca3..e4266dd 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -302,5 +302,6 @@ 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 */
-- 
2.4.3

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[PATCH v5 00/39] Richacls Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 34/39] sunrpc: Allow to demand-allocate pages to encode into Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 10/39] richacl: Permission check algorithm Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 28/39] nfsd: Keep list of acls to dispose of in compoundargs Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 30/39] nfsd: Add richacl support Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 35/39] sunrpc: Add xdr_init_encode_pages Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 14/39] richacl: Create-time inheritance Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 33/39] ext4: Don't allow unmapped identifiers in richacls Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 36/39] nfs: Fix GETATTR bitmap verification Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 13/39] richacl: Check if an acl is equivalent to a file mode Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:10 +0200
  [PATCH v5 15/39] richacl: Automatic Inheritance Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 18/39] ext4: Add richacl support Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 24/39] richacl: Set the other permissions to the other mask Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 21/39] richacl: Move everyone@ aces down the acl Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 19/39] ext4: Add richacl feature flag Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 27/39] richacl: Create richacl from mode values Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 31/39] nfsd: Add support for the v4.1 dacl attribute Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 22/39] richacl: Propagate everyone@ permissions to other aces Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 17/39] vfs: Add richacl permission checking Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 26/39] richacl: Apply the file masks to a richacl Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 32/39] richacl: Add support for unmapped identifiers Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 20/39] richacl: acl editing helper functions Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 23/39] richacl: Set the owner permissions to the owner mask Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 25/39] richacl: Isolate the owner and group classes Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:20 +0200
  [PATCH v5 08/39] richacl: Compute maximum file masks from an acl Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 02/39] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 03/39] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD permission flags Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 01/39] vfs: Add IS_ACL() and IS_RICHACL() tests Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 11/39] vfs: Cache base_acl objects in inodes Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 05/39] vfs: Add permission flags for setting file attributes Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 12/39] vfs: Cache richacl in struct inode Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 07/39] richacl: Permission mapping functions Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 04/39] vfs: Make the inode passed to inode_change_ok non-const Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 16/39] richacl: xattr mapping functions Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200
  [PATCH v5 09/39] richacl: Update the file masks in chmod() Andreas Gruenbacher <andreas.gruenbacher@gmail.com> - 2015-07-22 15:30 +0200

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