[PATCH -V2 05/16] richacl: Permission mapping functions

Aneesh Kumar K.V
2010-07-02T18:48:08Z

We need to map from POSIX permissions to NFSv4 permissions when a
chmod() is done, from NFSv4 permissions to POSIX permissions when an acl
is set (which implicitly sets the file permission bits), and from the
MAY_READ/MAY_WRITE/MAY_EXEC/MAY_APPEND flags to NFSv4 permissions when
doing an access check in a richacl.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/richacl_base.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++
include/linux/richacl.h | 27 +++++++++++++
2 files changed, 125 insertions(+), 0 deletions(-)

diff --git a/fs/richacl_base.c b/fs/richacl_base.c
index 99ed0ca..bfc0abf4 100644
--- a/fs/richacl_base.c
+++ b/fs/richacl_base.c
@@ -69,6 +69,104 @@ richacl_clone(const struct richacl *acl)
}

/**
+ * richacl_mask_to_mode - compute the file permission bits which correspond to @mask
+ * @mask: %ACE4_* permission mask
+ *
+ * See richacl_masks_to_mode().
+ */
+static int
+richacl_mask_to_mode(unsigned int mask)
+{
+ int mode = 0;
+
+ if (mask & ACE4_POSIX_MODE_READ)
+ mode |= MAY_READ;
+ if (mask & ACE4_POSIX_MODE_WRITE)
+ mode |= MAY_WRITE;
+ if (mask & ACE4_POSIX_MODE_EXEC)
+ mode |= MAY_EXEC;
+
+ return mode;
+}
+
+/**
+ * richacl_masks_to_mode - compute the file permission bits from the file masks
+ *
+ * When setting a richacl, we set the file permission bits to indicate maximum
+ * permissions: for example, we set the Write permission when a mask contains
+ * ACE4_APPEND_DATA even if it does not also contain ACE4_WRITE_DATA.
+ *
+ * Permissions which are not in ACE4_POSIX_MODE_READ, ACE4_POSIX_MODE_WRITE, or
+ * ACE4_POSIX_MODE_EXEC cannot be represented in the file permission bits.
+ * Such permissions can still be effective, but not for new files or after a
+ * chmod(), and only if they were set explicitly, for example, by setting a
+ * richacl.
+ */
+int
+richacl_masks_to_mode(const struct richacl *acl)
+{
+ return richacl_mask_to_mode(acl->a_owner_mask) << 6 |
+ richacl_mask_to_mode(acl->a_group_mask) << 3 |
+ richacl_mask_to_mode(acl->a_other_mask);
+}
+EXPORT_SYMBOL_GPL(richacl_masks_to_mode);
+
+/**
+ * richacl_mode_to_mask - compute a file mask from the lowest three mode bits
+ *
+ * When the file permission bits of a file are set with chmod(), this specifies
+ * the maximum permissions that processes will get. All permissions beyond
+ * that will be removed from the file masks, and become ineffective.
+ *
+ * We also add in the permissions which are always allowed no matter what the
+ * acl says.
+ */
+unsigned int
+richacl_mode_to_mask(mode_t mode)
+{
+ unsigned int mask = ACE4_POSIX_ALWAYS_ALLOWED;
+
+ if (mode & MAY_READ)
+ mask |= ACE4_POSIX_MODE_READ;
+ if (mode & MAY_WRITE)
+ mask |= ACE4_POSIX_MODE_WRITE;
+ if (mode & MAY_EXEC)
+ mask |= ACE4_POSIX_MODE_EXEC;
+
+ return mask;
+}
+
+/**
+ * richacl_want_to_mask - convert the iop->permission want argument to a mask
+ * @want: @want argument of the permission inode operation
+ *
+ * When checking for append, @want is (MAY_WRITE | MAY_APPEND).
+ *
+ * Richacls use the iop->may_create and iop->may_delete hooks which are
+ * used for checking if creating and deleting files is allowed. These hooks do
+ * not use richacl_want_to_mask(), so we do not have to deal with mapping
+ * MAY_WRITE to ACE4_ADD_FILE, ACE4_ADD_SUBDIRECTORY, and ACE4_DELETE_CHILD
+ * here.
+ */
+unsigned int
+richacl_want_to_mask(int want)
+{
+ unsigned int mask = 0;
+
+ if (want & MAY_READ)
+ mask |= ACE4_READ_DATA;
+ if (want & MAY_APPEND)
+ mask |= ACE4_APPEND_DATA;
+ else if (want & MAY_WRITE)
+ mask |= ACE4_WRITE_DATA;
+ if (want & MAY_EXEC)
+ mask |= ACE4_EXECUTE;
+
+ return mask;
+}
+EXPORT_SYMBOL_GPL(richacl_want_to_mask);
+
+/**
* richace_is_same_identifier - are both identifiers the same?
*/
int
diff --git a/include/linux/richacl.h b/include/linux/richacl.h
index 92cc8b5..8b9f7ef 100644
--- a/include/linux/richacl.h
+++ b/include/linux/richacl.h
@@ -111,6 +111,30 @@ struct richacl {
ACE4_WRITE_OWNER | \
ACE4_SYNCHRONIZE)

+/*
+ * The POSIX permissions are supersets of the following NFSv4 permissions:
+ *
+ * - MAY_READ maps to READ_DATA or LIST_DIRECTORY, depending on the type
+ * of the file system object.
+ *
+ * - MAY_WRITE maps to WRITE_DATA or ACE4_APPEND_DATA for files, and to
+ * ADD_FILE, ACE4_ADD_SUBDIRECTORY, or ACE4_DELETE_CHILD for directories.
+ *
+ * - MAY_EXECUTE maps to ACE4_EXECUTE.
+ *
+ * (Some of these NFSv4 permissions have the same bit values.)
+ */
+#define ACE4_POSIX_MODE_READ ( \
+ ACE4_READ_DATA | ACE4_LIST_DIRECTORY)
+#define ACE4_POSIX_MODE_WRITE ( \
+ ACE4_WRITE_DATA | ACE4_ADD_FILE | \
+ ACE4_APPEND_DATA | ACE4_ADD_SUBDIRECTORY | \
+ ACE4_DELETE_CHILD)
+#define ACE4_POSIX_MODE_EXEC ( \
+ ACE4_EXECUTE)
+#define ACE4_POSIX_MODE_ALL (ACE4_POSIX_MODE_READ | ACE4_POSIX_MODE_WRITE | \
+ ACE4_POSIX_MODE_EXEC)
+
/* These permissions are always allowed no matter what the acl says. */
#define ACE4_POSIX_ALWAYS_ALLOWED ( \
ACE4_SYNCHRONIZE | \
@@ -241,5 +265,8 @@ extern struct richacl *richacl_alloc(int);
extern int richace_is_same_identifier(const struct richace *,
const struct richace *);
extern int richace_set_who(struct richace *, const char *);
+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(int);

#endif /* __RICHACL_H */
--
1.7.2.rc1