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From: Andreas Gruenbacher <agruenba@redhat.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Gruenbacher <agruenba@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Jeff Layton <jlayton@poochiereds.net>,
	Trond Myklebust <trond.myklebust@primarydata.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Dave Chinner <david@fromorbit.com>,
	linux-ext4@vger.kernel.org, xfs@oss.sgi.com,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org,
	linux-api@vger.kernel.org
Subject: [PATCH v21 09/22] richacl: Permission check algorithm
Date: Tue, 10 May 2016 00:02:42 +0200	[thread overview]
Message-ID: <1462831375-23017-10-git-send-email-agruenba@redhat.com> (raw)
In-Reply-To: <1462831375-23017-1-git-send-email-agruenba@redhat.com>

A richacl roughly grants a requested access if the NFSv4 acl in the
richacl grants the requested permissions according to the NFSv4
permission check algorithm and the file mask that applies to the process
includes the requested permissions.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: "J. Bruce Fields" <bfields@fieldses.org>
---
 fs/richacl.c            | 128 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/richacl.h |   1 +
 2 files changed, 129 insertions(+)

diff --git a/fs/richacl.c b/fs/richacl.c
index 056228f..cb0ef3f 100644
--- a/fs/richacl.c
+++ b/fs/richacl.c
@@ -338,3 +338,131 @@ restart:
 	acl->a_flags &= ~(RICHACL_WRITE_THROUGH | RICHACL_MASKED);
 }
 EXPORT_SYMBOL_GPL(richacl_compute_max_masks);
+
+/**
+ * richacl_permission  -  richacl permission check algorithm
+ * @inode:	inode to check
+ * @acl:	rich acl of the inode
+ * @want:	requested access (MAY_* flags)
+ *
+ * Checks if the current process is granted @mask flags in @acl.
+ */
+int
+richacl_permission(struct inode *inode, const struct richacl *acl,
+		   int want)
+{
+	const struct richace *ace;
+	unsigned int mask = richacl_want_to_mask(want);
+	unsigned int requested = mask, denied = 0;
+	int in_owning_group = in_group_p(inode->i_gid);
+	int in_owner_or_group_class = in_owning_group;
+
+	/*
+	 * A process is
+	 *   - in the owner file class if it owns the file,
+	 *   - in the group file class if it is in the file's owning group or
+	 *     it matches any of the user or group entries, and
+	 *   - in the other file class otherwise.
+	 * The file class is only relevant for determining which file mask to
+	 * apply, which only happens for masked acls.
+	 */
+	if (acl->a_flags & RICHACL_MASKED) {
+		if ((acl->a_flags & RICHACL_WRITE_THROUGH) &&
+		    uid_eq(current_fsuid(), inode->i_uid)) {
+			denied = requested & ~acl->a_owner_mask;
+			goto out;
+		}
+	} else {
+		/*
+		 * When the acl is not masked, there is no need to determine if
+		 * the process is in the group class and we can break out
+		 * earlier of the loop below.
+		 */
+		in_owner_or_group_class = 1;
+	}
+
+	/*
+	 * Check if the acl grants the requested access and determine which
+	 * file class the process is in.
+	 */
+	richacl_for_each_entry(ace, acl) {
+		unsigned int ace_mask = ace->e_mask;
+
+		if (richace_is_inherit_only(ace))
+			continue;
+		if (richace_is_owner(ace)) {
+			if (!uid_eq(current_fsuid(), inode->i_uid))
+				continue;
+			goto entry_matches_owner;
+		} else if (richace_is_group(ace)) {
+			if (!in_owning_group)
+				continue;
+		} else if (richace_is_unix_user(ace)) {
+			if (!uid_eq(current_fsuid(), ace->e_id.uid))
+				continue;
+			if (uid_eq(current_fsuid(), inode->i_uid))
+				goto entry_matches_owner;
+		} else if (richace_is_unix_group(ace)) {
+			if (!in_group_p(ace->e_id.gid))
+				continue;
+		} else
+			goto entry_matches_everyone;
+
+		/*
+		 * Apply the group file mask to entries other than owner@ and
+		 * everyone@ or user entries matching the owner.  This ensures
+		 * that we grant the same permissions as the acl computed by
+		 * richacl_apply_masks().
+		 *
+		 * Without this restriction, the following richacl would grant
+		 * rw access to processes which are both the owner and in the
+		 * owning group, but not to other users in the owning group,
+		 * which could not be represented without masks:
+		 *
+		 *  owner:rw::mask
+		 *  group@:rw::allow
+		 */
+		if ((acl->a_flags & RICHACL_MASKED) && richace_is_allow(ace))
+			ace_mask &= acl->a_group_mask;
+
+entry_matches_owner:
+		/* The process is in the owner or group file class. */
+		in_owner_or_group_class = 1;
+
+entry_matches_everyone:
+		/* Check which mask flags the ACE allows or denies. */
+		if (richace_is_deny(ace))
+			denied |= ace_mask & mask;
+		mask &= ~ace_mask;
+
+		/*
+		 * Keep going until we know which file class
+		 * the process is in.
+		 */
+		if (!mask && in_owner_or_group_class)
+			break;
+	}
+	denied |= mask;
+
+	if (acl->a_flags & RICHACL_MASKED) {
+		/*
+		 * The file class a process is in determines which file mask
+		 * applies.  Check if that file mask also grants the requested
+		 * access.
+		 */
+		if (uid_eq(current_fsuid(), inode->i_uid))
+			denied |= requested & ~acl->a_owner_mask;
+		else if (in_owner_or_group_class)
+			denied |= requested & ~acl->a_group_mask;
+		else {
+			if (acl->a_flags & RICHACL_WRITE_THROUGH)
+				denied = requested & ~acl->a_other_mask;
+			else
+				denied |= requested & ~acl->a_other_mask;
+		}
+	}
+
+out:
+	return denied ? -EACCES : 0;
+}
+EXPORT_SYMBOL_GPL(richacl_permission);
diff --git a/include/linux/richacl.h b/include/linux/richacl.h
index 3559b2c..be9fb65 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -179,5 +179,6 @@ extern int richacl_masks_to_mode(const struct richacl *);
 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);
 
 #endif /* __RICHACL_H */
-- 
2.5.5

  parent reply	other threads:[~2016-05-09 22:04 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-09 22:02 [PATCH v21 00/22] Richacls Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 01/22] vfs: Add IS_ACL() and IS_RICHACL() tests Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 02/22] vfs: Add MAY_CREATE_FILE and MAY_CREATE_DIR permission flags Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 03/22] vfs: Add MAY_DELETE_SELF and MAY_DELETE_CHILD " Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 04/22] vfs: Make the inode passed to inode_change_ok non-const Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 05/22] vfs: Add permission flags for setting file attributes Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 06/22] richacl: In-memory representation and helper functions Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 07/22] richacl: Permission mapping functions Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 08/22] richacl: Compute maximum file masks from an acl Andreas Gruenbacher
2016-05-09 22:02 ` Andreas Gruenbacher [this message]
2016-05-09 22:02 ` [PATCH v21 10/22] posix_acl: Improve xattr fixup code Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 11/22] vfs: Cache base_acl objects in inodes Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 12/22] vfs: Add get_richacl and set_richacl inode operations Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 13/22] vfs: Cache richacl in struct inode Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 14/22] richacl: Update the file masks in chmod() Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 15/22] richacl: Check if an acl is equivalent to a file mode Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 16/22] richacl: Create-time inheritance Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 17/22] richacl: Automatic Inheritance Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 18/22] richacl: xattr mapping functions Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 19/22] richacl: Add richacl xattr handler Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 20/22] vfs: Add richacl permission checking Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 21/22] ext4: Add richacl support Andreas Gruenbacher
2016-05-09 22:02 ` [PATCH v21 22/22] ext4: Add richacl feature flag Andreas Gruenbacher
2016-05-10  4:18 ` [PATCH v21 00/22] Richacls Volker Lendecke
2016-05-10  8:11   ` Jeremy Allison
2016-05-10  8:20     ` Volker Lendecke
2016-05-10 15:55     ` Frank Filz

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