Constify structures containing function pointers

The PaX team modified the kernel's modpost to report writeable function
pointers as section mismatches because they are potential exploit
targets. We could ignore the warnings, but their presence can obscure
actual issues. Proper const correctness can also catch programming
mistakes.

Building the kernel modules against a PaX/GrSecurity patched Linux 3.4.2
kernel reports 133 section mismatches prior to this patch. This patch
eliminates 130 of them. The quantity of writeable function pointers
eliminated by constifying each structure is as follows:

vdev_opts_t             52
zil_replay_func_t       24
zio_compress_info_t     24
zio_checksum_info_t     9
space_map_ops_t         7
arc_byteswap_func_t     5

The remaining 3 writeable function pointers cannot be addressed by this
patch. 2 of them are in zpl_fs_type. The kernel's sget function requires
that this be non-const. The final writeable function pointer is created
by SPL_SHRINKER_DECLARE. The kernel's set_shrinker() and
remove_shrinker() functions also require that this be non-const.

Signed-off-by: Richard Yao <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #1300

7 files changed, 10 insertions, 10 deletions

diff --git a/include/sys/dmu.h b/include/sys/dmu.h
index 2a3a76486..eb6a465c4 100644
--- a/include/sys/dmu.h
+++ b/include/sys/dmu.h
@@ -641,7 +641,7 @@ typedef struct dmu_object_info {
 	uint64_t doi_fill_count;		/* number of non-empty blocks */
 } dmu_object_info_t;
 
-typedef void arc_byteswap_func_t(void *buf, size_t size);
+typedef void (*const arc_byteswap_func_t)(void *buf, size_t size);
 
 typedef struct dmu_object_type_info {
 	dmu_object_byteswap_t	ot_byteswap;
@@ -649,8 +649,8 @@ typedef struct dmu_object_type_info {
 	char			*ot_name;
 } dmu_object_type_info_t;
 
-typedef struct dmu_object_byteswap_info {
-	arc_byteswap_func_t	*ob_func;
+typedef const struct dmu_object_byteswap_info {
+	arc_byteswap_func_t	 ob_func;
 	char			*ob_name;
 } dmu_object_byteswap_info_t;
 
diff --git a/include/sys/space_map.h b/include/sys/space_map.h
index 6f935c9db..332299724 100644
--- a/include/sys/space_map.h
+++ b/include/sys/space_map.h
@@ -33,7 +33,7 @@
 extern "C" {
 #endif
 
-typedef struct space_map_ops space_map_ops_t;
+typedef const struct space_map_ops space_map_ops_t;
 
 typedef struct space_map {
 	avl_tree_t	sm_root;	/* AVL tree of map segments */
diff --git a/include/sys/vdev_impl.h b/include/sys/vdev_impl.h
index 4133f2cf3..964ee2407 100644
--- a/include/sys/vdev_impl.h
+++ b/include/sys/vdev_impl.h
@@ -67,7 +67,7 @@ typedef void	vdev_state_change_func_t(vdev_t *vd, int, int);
 typedef void	vdev_hold_func_t(vdev_t *vd);
 typedef void	vdev_rele_func_t(vdev_t *vd);
 
-typedef struct vdev_ops {
+typedef const struct vdev_ops {
 	vdev_open_func_t		*vdev_op_open;
 	vdev_close_func_t		*vdev_op_close;
 	vdev_asize_func_t		*vdev_op_asize;
diff --git a/include/sys/zfs_znode.h b/include/sys/zfs_znode.h
index 41233547b..bdddcc366 100644
--- a/include/sys/zfs_znode.h
+++ b/include/sys/zfs_znode.h
@@ -371,7 +371,7 @@ extern void zfs_unmap_page(page_t *, caddr_t);
 #endif /* HAVE_UIO_RW */
 
 extern zil_get_data_t zfs_get_data;
-extern zil_replay_func_t *zfs_replay_vector[TX_MAX_TYPE];
+extern zil_replay_func_t zfs_replay_vector[TX_MAX_TYPE];
 extern int zfsfstype;
 
 #endif /* _KERNEL */
diff --git a/include/sys/zil.h b/include/sys/zil.h
index f786f0c9f..589e28f83 100644
--- a/include/sys/zil.h
+++ b/include/sys/zil.h
@@ -436,7 +436,7 @@ typedef int zil_parse_blk_func_t(zilog_t *zilog, blkptr_t *bp, void *arg,
     uint64_t txg);
 typedef int zil_parse_lr_func_t(zilog_t *zilog, lr_t *lr, void *arg,
     uint64_t txg);
-typedef int zil_replay_func_t(void *, char *, boolean_t);
+typedef int (*const zil_replay_func_t)(void *, char *, boolean_t);
 typedef int zil_get_data_t(void *arg, lr_write_t *lr, char *dbuf, zio_t *zio);
 
 extern int zil_parse(zilog_t *zilog, zil_parse_blk_func_t *parse_blk_func,
@@ -452,7 +452,7 @@ extern zilog_t	*zil_open(objset_t *os, zil_get_data_t *get_data);
 extern void	zil_close(zilog_t *zilog);
 
 extern void	zil_replay(objset_t *os, void *arg,
-    zil_replay_func_t *replay_func[TX_MAX_TYPE]);
+    zil_replay_func_t replay_func[TX_MAX_TYPE]);
 extern boolean_t zil_replaying(zilog_t *zilog, dmu_tx_t *tx);
 extern void	zil_destroy(zilog_t *zilog, boolean_t keep_first);
 extern void	zil_destroy_sync(zilog_t *zilog, dmu_tx_t *tx);
diff --git a/include/sys/zio_checksum.h b/include/sys/zio_checksum.h
index 0956c04ab..de89bc9a7 100644
--- a/include/sys/zio_checksum.h
+++ b/include/sys/zio_checksum.h
@@ -39,7 +39,7 @@ typedef void zio_checksum_t(const void *data, uint64_t size, zio_cksum_t *zcp);
 /*
  * Information about each checksum function.
  */
-typedef struct zio_checksum_info {
+typedef const struct zio_checksum_info {
 	zio_checksum_t	*ci_func[2]; /* checksum function for each byteorder */
 	int		ci_correctable;	/* number of correctable bits	*/
 	int		ci_eck;		/* uses zio embedded checksum? */
diff --git a/include/sys/zio_compress.h b/include/sys/zio_compress.h
index 49946af4b..bd051f185 100644
--- a/include/sys/zio_compress.h
+++ b/include/sys/zio_compress.h
@@ -44,7 +44,7 @@ typedef int zio_decompress_func_t(void *src, void *dst,
 /*
  * Information about each compression function.
  */
-typedef struct zio_compress_info {
+typedef const struct zio_compress_info {
 	zio_compress_func_t	*ci_compress;	/* compression function */
 	zio_decompress_func_t	*ci_decompress;	/* decompression function */
 	int			ci_level;	/* level parameter */