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

5 files changed, 43 insertions, 43 deletions

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index b7499ee96..da070cd26 100644
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -2802,10 +2802,10 @@ arc_read_done(zio_t *zio)
 	if (BP_SHOULD_BYTESWAP(zio->io_bp) && zio->io_error == 0) {
 		dmu_object_byteswap_t bswap =
 		    DMU_OT_BYTESWAP(BP_GET_TYPE(zio->io_bp));
-		arc_byteswap_func_t *func = BP_GET_LEVEL(zio->io_bp) > 0 ?
-		    byteswap_uint64_array :
-		    dmu_ot_byteswap[bswap].ob_func;
-		func(buf->b_data, hdr->b_size);
+		if (BP_GET_LEVEL(zio->io_bp) > 0)
+		    byteswap_uint64_array(buf->b_data, hdr->b_size);
+		else
+		    dmu_ot_byteswap[bswap].ob_func(buf->b_data, hdr->b_size);
 	}
 
 	arc_cksum_compute(buf, B_FALSE);
diff --git a/module/zfs/sa.c b/module/zfs/sa.c
index f4d264f71..581cf4b0d 100644
--- a/module/zfs/sa.c
+++ b/module/zfs/sa.c
@@ -136,7 +136,7 @@ static int sa_modify_attrs(sa_handle_t *hdl, sa_attr_type_t newattr,
     sa_data_op_t action, sa_data_locator_t *locator, void *datastart,
     uint16_t buflen, dmu_tx_t *tx);
 
-arc_byteswap_func_t *sa_bswap_table[] = {
+arc_byteswap_func_t sa_bswap_table[] = {
 	byteswap_uint64_array,
 	byteswap_uint32_array,
 	byteswap_uint16_array,
diff --git a/module/zfs/zfs_replay.c b/module/zfs/zfs_replay.c
index aa6366e11..813250c37 100644
--- a/module/zfs/zfs_replay.c
+++ b/module/zfs/zfs_replay.c
@@ -910,26 +910,26 @@ zfs_replay_acl(zfs_sb_t *zsb, lr_acl_t *lr, boolean_t byteswap)
 /*
  * Callback vectors for replaying records
  */
-zil_replay_func_t *zfs_replay_vector[TX_MAX_TYPE] = {
-	(zil_replay_func_t *)zfs_replay_error,		/* no such type */
-	(zil_replay_func_t *)zfs_replay_create,		/* TX_CREATE */
-	(zil_replay_func_t *)zfs_replay_create,		/* TX_MKDIR */
-	(zil_replay_func_t *)zfs_replay_create,		/* TX_MKXATTR */
-	(zil_replay_func_t *)zfs_replay_create,		/* TX_SYMLINK */
-	(zil_replay_func_t *)zfs_replay_remove,		/* TX_REMOVE */
-	(zil_replay_func_t *)zfs_replay_remove,		/* TX_RMDIR */
-	(zil_replay_func_t *)zfs_replay_link,		/* TX_LINK */
-	(zil_replay_func_t *)zfs_replay_rename,		/* TX_RENAME */
-	(zil_replay_func_t *)zfs_replay_write,		/* TX_WRITE */
-	(zil_replay_func_t *)zfs_replay_truncate,	/* TX_TRUNCATE */
-	(zil_replay_func_t *)zfs_replay_setattr,	/* TX_SETATTR */
-	(zil_replay_func_t *)zfs_replay_acl_v0,		/* TX_ACL_V0 */
-	(zil_replay_func_t *)zfs_replay_acl,		/* TX_ACL */
-	(zil_replay_func_t *)zfs_replay_create_acl,	/* TX_CREATE_ACL */
-	(zil_replay_func_t *)zfs_replay_create,		/* TX_CREATE_ATTR */
-	(zil_replay_func_t *)zfs_replay_create_acl,	/* TX_CREATE_ACL_ATTR */
-	(zil_replay_func_t *)zfs_replay_create_acl,	/* TX_MKDIR_ACL */
-	(zil_replay_func_t *)zfs_replay_create,		/* TX_MKDIR_ATTR */
-	(zil_replay_func_t *)zfs_replay_create_acl,	/* TX_MKDIR_ACL_ATTR */
-	(zil_replay_func_t *)zfs_replay_write2,		/* TX_WRITE2 */
+zil_replay_func_t zfs_replay_vector[TX_MAX_TYPE] = {
+	(zil_replay_func_t)zfs_replay_error,		/* no such type */
+	(zil_replay_func_t)zfs_replay_create,		/* TX_CREATE */
+	(zil_replay_func_t)zfs_replay_create,		/* TX_MKDIR */
+	(zil_replay_func_t)zfs_replay_create,		/* TX_MKXATTR */
+	(zil_replay_func_t)zfs_replay_create,		/* TX_SYMLINK */
+	(zil_replay_func_t)zfs_replay_remove,		/* TX_REMOVE */
+	(zil_replay_func_t)zfs_replay_remove,		/* TX_RMDIR */
+	(zil_replay_func_t)zfs_replay_link,		/* TX_LINK */
+	(zil_replay_func_t)zfs_replay_rename,		/* TX_RENAME */
+	(zil_replay_func_t)zfs_replay_write,		/* TX_WRITE */
+	(zil_replay_func_t)zfs_replay_truncate,		/* TX_TRUNCATE */
+	(zil_replay_func_t)zfs_replay_setattr,		/* TX_SETATTR */
+	(zil_replay_func_t)zfs_replay_acl_v0,		/* TX_ACL_V0 */
+	(zil_replay_func_t)zfs_replay_acl,		/* TX_ACL */
+	(zil_replay_func_t)zfs_replay_create_acl,	/* TX_CREATE_ACL */
+	(zil_replay_func_t)zfs_replay_create,		/* TX_CREATE_ATTR */
+	(zil_replay_func_t)zfs_replay_create_acl,	/* TX_CREATE_ACL_ATTR */
+	(zil_replay_func_t)zfs_replay_create_acl,	/* TX_MKDIR_ACL */
+	(zil_replay_func_t)zfs_replay_create,		/* TX_MKDIR_ATTR */
+	(zil_replay_func_t)zfs_replay_create_acl,	/* TX_MKDIR_ACL_ATTR */
+	(zil_replay_func_t)zfs_replay_write2,		/* TX_WRITE2 */
 };
diff --git a/module/zfs/zil.c b/module/zfs/zil.c
index c9618c13e..99d932fc0 100644
--- a/module/zfs/zil.c
+++ b/module/zfs/zil.c
@@ -1956,7 +1956,7 @@ zil_resume(zilog_t *zilog)
 }
 
 typedef struct zil_replay_arg {
-	zil_replay_func_t **zr_replay;
+	zil_replay_func_t *zr_replay;
 	void		*zr_arg;
 	boolean_t	zr_byteswap;
 	char		*zr_lr;
@@ -2075,7 +2075,7 @@ zil_incr_blks(zilog_t *zilog, blkptr_t *bp, void *arg, uint64_t claim_txg)
  * If this dataset has a non-empty intent log, replay it and destroy it.
  */
 void
-zil_replay(objset_t *os, void *arg, zil_replay_func_t *replay_func[TX_MAX_TYPE])
+zil_replay(objset_t *os, void *arg, zil_replay_func_t replay_func[TX_MAX_TYPE])
 {
 	zilog_t *zilog = dmu_objset_zil(os);
 	const zil_header_t *zh = zilog->zl_header;
diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c
index c6cfac26d..f8e325676 100644
--- a/module/zfs/zvol.c
+++ b/module/zfs/zvol.c
@@ -453,20 +453,20 @@ zvol_replay_err(zvol_state_t *zv, lr_t *lr, boolean_t byteswap)
  * Callback vectors for replaying records.
  * Only TX_WRITE is needed for zvol.
  */
-zil_replay_func_t *zvol_replay_vector[TX_MAX_TYPE] = {
-	(zil_replay_func_t *)zvol_replay_err,	/* no such transaction type */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_CREATE */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_MKDIR */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_MKXATTR */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_SYMLINK */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_REMOVE */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_RMDIR */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_LINK */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_RENAME */
-	(zil_replay_func_t *)zvol_replay_write,	/* TX_WRITE */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_TRUNCATE */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_SETATTR */
-	(zil_replay_func_t *)zvol_replay_err,	/* TX_ACL */
+zil_replay_func_t zvol_replay_vector[TX_MAX_TYPE] = {
+	(zil_replay_func_t)zvol_replay_err,	/* no such transaction type */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_CREATE */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_MKDIR */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_MKXATTR */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_SYMLINK */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_REMOVE */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_RMDIR */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_LINK */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_RENAME */
+	(zil_replay_func_t)zvol_replay_write,	/* TX_WRITE */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_TRUNCATE */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_SETATTR */
+	(zil_replay_func_t)zvol_replay_err,	/* TX_ACL */
 };
 
 /*