[PATCH v5 25/39] richacl: Isolate the owner and group classes

From	Andreas Gruenbacher <andreas.gruenbacher@gmail.com>
Newsgroups	linux.kernel
Subject	[PATCH v5 25/39] richacl: Isolate the owner and group classes
Date	2015-07-22 15:20 +0200
Message-ID	<pP26f-7TN-71@gated-at.bofh.it> (permalink)
References	<pP1Wx-7Id-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

From: Andreas Gruenbacher <agruenba@redhat.com>

When applying the file masks to an acl, we need to ensure that no
process gets more permissions than allowed by its file mask.

This may require inserting an owner@ deny ace to ensure this if the
owner mask contains fewer permissions than the group or other mask.  For
example, when applying mode 0466 to the following acl:

   everyone@:rw::allow

A deny ace needs to be inserted so that the owner won't get elevated
write access:

   owner@:w::deny
   everyone@:rw::allow

Likewise, we may need to insert group class deny aces if the group mask
contains fewer permissions than the other mask.  For example, when
applying mode 0646 to the following acl:

   owner@:rw::allow
   everyone@:rw::allow

A deny ace needs to be inserted so that the owning group won't get
elevated write access:

   owner@:rw::allow
   group@:w::deny
   everyone@:rw::allow

Signed-off-by: Andreas Gruenbacher <agruen@kernel.org>
---
 fs/richacl_compat.c | 229 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 229 insertions(+)

diff --git a/fs/richacl_compat.c b/fs/richacl_compat.c
index 438859c..f18f59c 100644
--- a/fs/richacl_compat.c
+++ b/fs/richacl_compat.c
@@ -474,3 +474,232 @@ richacl_set_other_permissions(struct richacl_alloc *alloc)
 		richace_change_mask(alloc, &ace, other_mask);
 	return 0;
 }
+
+/**
+ * richacl_max_allowed  -  maximum permissions that anybody is allowed
+ */
+static unsigned int
+richacl_max_allowed(struct richacl *acl)
+{
+	struct richace *ace;
+	unsigned int allowed = 0;
+
+	richacl_for_each_entry_reverse(ace, acl) {
+		if (richace_is_inherit_only(ace))
+			continue;
+		if (richace_is_allow(ace))
+			allowed |= ace->e_mask;
+		else if (richace_is_deny(ace)) {
+			if (richace_is_everyone(ace))
+				allowed &= ~ace->e_mask;
+		}
+	}
+	return allowed;
+}
+
+/**
+ * richacl_isolate_owner_class  -  limit the owner class to the owner file mask
+ * @alloc:	acl and number of allocated entries
+ *
+ * POSIX requires that after a chmod, the owner class is granted no more
+ * permissions than the owner file permission bits.  For richacls, this
+ * means that the owner class must not be granted any permissions that the
+ * owner mask does not include.
+ *
+ * When we apply file masks to an acl which grant more permissions to the group
+ * or other class than to the owner class, we may end up in a situation where
+ * the owner is granted additional permissions from other aces.  For example,
+ * given this acl:
+ *
+ *    everyone:rwx::allow
+ *
+ * when file masks corresponding to mode 0466 are applied, after
+ * richacl_propagate_everyone() and __richacl_apply_masks(), we end up with:
+ *
+ *    owner@:r::allow
+ *    everyone@:rw::allow
+ *
+ * This acl still grants the owner rw access through the everyone@ allow ace.
+ * To fix this, we must deny the owner w access:
+ *
+ *    owner@:w::deny
+ *    owner@:r::allow
+ *    everyone@:rw::allow
+ */
+static int
+richacl_isolate_owner_class(struct richacl_alloc *alloc)
+{
+	struct richace *ace;
+	unsigned int allowed = 0;
+
+	allowed = richacl_max_allowed(alloc->acl);
+	if (allowed & ~alloc->acl->a_owner_mask) {
+		/*
+		 * Figure out if we can update an existig OWNER@ DENY entry.
+		 */
+		richacl_for_each_entry(ace, alloc->acl) {
+			if (richace_is_inherit_only(ace))
+				continue;
+			if (richace_is_deny(ace)) {
+				if (richace_is_owner(ace))
+					break;
+			} else if (richace_is_allow(ace)) {
+				ace = alloc->acl->a_entries + alloc->acl->a_count;
+				break;
+			}
+		}
+		if (ace != alloc->acl->a_entries + alloc->acl->a_count) {
+			if (richace_change_mask(alloc, &ace, ace->e_mask |
+					(allowed & ~alloc->acl->a_owner_mask)))
+				return -1;
+		} else {
+			/* Insert an owner@ deny entry at the front. */
+			ace = alloc->acl->a_entries;
+			if (richacl_insert_entry(alloc, &ace))
+				return -1;
+			ace->e_type = RICHACE_ACCESS_DENIED_ACE_TYPE;
+			ace->e_flags = RICHACE_SPECIAL_WHO;
+			ace->e_mask = allowed & ~alloc->acl->a_owner_mask;
+			ace->e_id.special = RICHACE_OWNER_SPECIAL_ID;
+		}
+	}
+	return 0;
+}
+
+/**
+ * __richacl_isolate_who  -  isolate entry from everyone@ allow entry
+ * @alloc:	acl and number of allocated entries
+ * @who:	identifier to isolate
+ * @deny:	permissions this identifier should not be allowed
+ *
+ * See richacl_isolate_group_class().
+ */
+static int
+__richacl_isolate_who(struct richacl_alloc *alloc, struct richace *who,
+		      unsigned int deny)
+{
+	struct richacl *acl = alloc->acl;
+	struct richace *ace;
+	int n;
+	/*
+	 * Compute the permissions already denied to @who.
+	 */
+	richacl_for_each_entry(ace, acl) {
+		if (richace_is_inherit_only(ace))
+			continue;
+		if (richace_is_same_identifier(ace, who) &&
+		    richace_is_deny(ace))
+			deny &= ~ace->e_mask;
+	}
+	if (!deny)
+		return 0;
+
+	/*
+	 * Figure out if we can update an existig deny entry.  Start from the
+	 * entry before the trailing everyone@ allow entry. We will not hit
+	 * everyone@ entries in the loop.
+	 */
+	for (n = acl->a_count - 2; n != -1; n--) {
+		ace = acl->a_entries + n;
+		if (richace_is_inherit_only(ace))
+			continue;
+		if (richace_is_deny(ace)) {
+			if (richace_is_same_identifier(ace, who))
+				break;
+		} else if (richace_is_allow(ace) &&
+			   (ace->e_mask & deny)) {
+			n = -1;
+			break;
+		}
+	}
+	if (n != -1) {
+		if (richace_change_mask(alloc, &ace, ace->e_mask | deny))
+			return -1;
+	} else {
+		/*
+		 * Insert a new entry before the trailing everyone@ deny entry.
+		 */
+		struct richace who_copy;
+
+		richace_copy(&who_copy, who);
+		ace = acl->a_entries + acl->a_count - 1;
+		if (richacl_insert_entry(alloc, &ace))
+			return -1;
+		richace_copy(ace, &who_copy);
+		ace->e_type = RICHACE_ACCESS_DENIED_ACE_TYPE;
+		richace_clear_inheritance_flags(ace);
+		ace->e_mask = deny;
+	}
+	return 0;
+}
+
+/**
+ * richacl_isolate_group_class  -  limit the group class to the group file mask
+ * @alloc:	acl and number of allocated entries
+ *
+ * POSIX requires that after a chmod, the group class is granted no more
+ * permissions than the group file permission bits.  For richacls, this
+ * means that the group class must not be granted any permissions that the
+ * group mask does not include.
+ *
+ * When we apply file masks to an acl which grant more permissions to the other
+ * class than to the group class, we may end up in a situation where processes
+ * in the group class are granted additional permission from other aces.  For
+ * example, given this acl:
+ *
+ *    joe:rwx::allow
+ *    everyone:rwx::allow
+ *
+ * when file masks corresponding to mode 0646 are applied, after
+ * richacl_propagate_everyone() and __richacl_apply_masks(), we end up with:
+ *
+ *    joe:r::allow
+ *    owner@:rw::allow
+ *    group@:r::allow
+ *    everyone@:rw::allow
+ *
+ * This acl still grants joe and group@ rw access through the everyone@ allow
+ * ace.  To fix this, we must deny w access to group class aces before the
+ * everyone@ allow ace at the end of the acl:
+ *
+ *    joe:r::allow
+ *    owner@:rw::allow
+ *    group@:r::allow
+ *    joe:w::deny
+ *    group@:w::deny
+ *    everyone@:rw::allow
+ */
+static int
+richacl_isolate_group_class(struct richacl_alloc *alloc)
+{
+	struct richace who = {
+		.e_flags = RICHACE_SPECIAL_WHO,
+		.e_id.special = RICHACE_GROUP_SPECIAL_ID,
+	};
+	unsigned int deny;
+
+	deny = alloc->acl->a_other_mask & ~alloc->acl->a_group_mask;
+
+	if (deny) {
+		unsigned int n;
+
+		if (__richacl_isolate_who(alloc, &who, deny))
+			return -1;
+		/*
+		 * Start from the entry before the trailing everyone@ allow
+		 * entry.  We will not hit everyone@ entries in the loop.
+		 */
+		for (n = alloc->acl->a_count - 1; n != -1; n--) {
+			struct richace *ace = alloc->acl->a_entries + n;
+
+			if (richace_is_inherit_only(ace) ||
+			    richace_is_owner(ace) ||
+			    richace_is_group(ace) ||
+			    richace_is_everyone(ace))
+				continue;
+			if (__richacl_isolate_who(alloc, ace, deny))
+				return -1;
+		}
+	}
+	return 0;
+}
-- 
2.4.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Thread

[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

csiph-web