[PATCH v13 05/51] vfs: Add permission flags for setting file attributes

Andreas Gruenbacher
2015-11-03T15:18:12Z

Richacls support permissions that allow to take ownership of a file,
change the file permissions, and set the file timestamps. Support that
by introducing new permission mask flags and by checking for those mask
flags in inode_change_ok().

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
---
fs/attr.c | 79 +++++++++++++++++++++++++++++++++++++++++++++---------
include/linux/fs.h | 3 +++
2 files changed, 70 insertions(+), 12 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index 328be71..85483e0 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -17,6 +17,65 @@
#include <linux/ima.h>

/**
+ * inode_extended_permission - permissions beyond read/write/execute
+ *
+ * Check for permissions that only richacls can currently grant.
+ */
+static int inode_extended_permission(struct inode *inode, int mask)
+{
+ if (!IS_RICHACL(inode))
+ return -EPERM;
+ return inode_permission(inode, mask);
+}
+
+static bool inode_uid_change_ok(struct inode *inode, kuid_t ia_uid)
+{
+ if (uid_eq(current_fsuid(), inode->i_uid) &&
+ uid_eq(ia_uid, inode->i_uid))
+ return true;
+ if (uid_eq(current_fsuid(), ia_uid) &&
+ inode_extended_permission(inode, MAY_TAKE_OWNERSHIP) == 0)
+ return true;
+ if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
+ return true;
+ return false;
+}
+
+static bool inode_gid_change_ok(struct inode *inode, kgid_t ia_gid)
+{
+ int in_group = in_group_p(ia_gid);
+ if (uid_eq(current_fsuid(), inode->i_uid) &&
+ (in_group || gid_eq(ia_gid, inode->i_gid)))
+ return true;
+ if (in_group && inode_extended_permission(inode, MAY_TAKE_OWNERSHIP) == 0)
+ return true;
+ if (capable_wrt_inode_uidgid(inode, CAP_CHOWN))
+ return true;
+ return false;
+}
+
+/**
+ * inode_owner_permitted_or_capable
+ *
+ * Check for permissions implicitly granted to the owner, like MAY_CHMOD or
+ * MAY_SET_TIMES. Equivalent to inode_owner_or_capable for file systems
+ * without support for those permissions.
+ */
+static bool inode_owner_permitted_or_capable(struct inode *inode, int mask)
+{
+ struct user_namespace *ns;
+
+ if (uid_eq(current_fsuid(), inode->i_uid))
+ return true;
+ if (inode_extended_permission(inode, mask) == 0)
+ return true;
+ ns = current_user_ns();
+ if (ns_capable(ns, CAP_FOWNER) && kuid_has_mapping(ns, inode->i_uid))
+ return true;
+ return false;
+}
+
+/**
* inode_change_ok - check if attribute changes to an inode are allowed
* @inode: inode to check
* @attr: attributes to change
@@ -47,22 +106,18 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)
return 0;

/* Make sure a caller can chown. */
- if ((ia_valid & ATTR_UID) &&
- (!uid_eq(current_fsuid(), inode->i_uid) ||
- !uid_eq(attr->ia_uid, inode->i_uid)) &&
- !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
- return -EPERM;
+ if (ia_valid & ATTR_UID)
+ if (!inode_uid_change_ok(inode, attr->ia_uid))
+ return -EPERM;

/* Make sure caller can chgrp. */
- if ((ia_valid & ATTR_GID) &&
- (!uid_eq(current_fsuid(), inode->i_uid) ||
- (!in_group_p(attr->ia_gid) && !gid_eq(attr->ia_gid, inode->i_gid))) &&
- !capable_wrt_inode_uidgid(inode, CAP_CHOWN))
- return -EPERM;
+ if (ia_valid & ATTR_GID)
+ if (!inode_gid_change_ok(inode, attr->ia_gid))
+ return -EPERM;

/* Make sure a caller can chmod. */
if (ia_valid & ATTR_MODE) {
- if (!inode_owner_or_capable(inode))
+ if (!inode_owner_permitted_or_capable(inode, MAY_CHMOD))
return -EPERM;
/* Also check the setgid bit! */
if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
@@ -73,7 +128,7 @@ int inode_change_ok(struct inode *inode, struct iattr *attr)

/* Check for setting the inode time. */
if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
- if (!inode_owner_or_capable(inode))
+ if (!inode_owner_permitted_or_capable(inode, MAY_SET_TIMES))
return -EPERM;
}

diff --git a/include/linux/fs.h b/include/linux/fs.h
index aab32c8..ba91a89 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -86,6 +86,9 @@ typedef void (dax_iodone_t)(struct buffer_head *bh_map, int uptodate);
#define MAY_CREATE_DIR 0x00000200
#define MAY_DELETE_CHILD 0x00000400
#define MAY_DELETE_SELF 0x00000800
+#define MAY_TAKE_OWNERSHIP 0x00001000
+#define MAY_CHMOD 0x00002000
+#define MAY_SET_TIMES 0x00004000

/*
* flags in file.f_mode. Note that FMODE_READ and FMODE_WRITE must correspond