Eliminate runtime function pointer mods in autotools checks

PaX/GrSecurity patched kernels implement a dialect of C that relies on a
GCC plugin for enforcement. A basic idea in this dialect is that
function pointers in structures should not change during runtime.
This causes code that modifies function pointers at runtime to fail to
compile in many instances. The autotools checks rely on whether or
not small test cases compile against a given kernel. Some
autotools checks assume some default case if other cases fail. When one
of these autotools checks tests a PaX/GrSecurity patched kernel by
modifying a function pointer at runtime, the default case will be used.

Early detection of such situations is possible by relying on compiler
warnings, which are compiler errors when --enable-debug is used.
Unfortunately, very few people build ZFS with --enable-debug. The more
common situation is that these issues manifest themselves as runtime
failures in the form of NULL pointer exceptions.

Previous patches that addressed such issues with PaX/GrSecurity
compatibility largely relied on rewriting autotools checks to avoid
runtime function pointer modification or the addition of PaX/GrSecurity
specific checks. This patch takes the previous work to its logical
conclusion by eliminating the use of runtime function pointer
modification. This permits the removal of PaX-specific autotools checks
in favor of ones that work across all supported kernels.

This should resolve issues that were reported to occur with
PaX/GrSecurity-patched Linux 3.7.5 kernels on Gentoo Linux.

https://bugs.gentoo.org/show_bug.cgi?id=457176

We should be able to prevent future regressions in PaX/GrSecurity
compatibility by ensuring that all changes to ZFSOnLinux avoid runtime
function pointer modification. At the same time, this does not solve the
issue of silent failures triggering default cases in the autotools
check, which is what permitted these regressions to become runtime
failures in the first place. This will need to be addressed in a future
patch.

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

10 files changed, 113 insertions, 150 deletions

diff --git a/config/kernel-bdev-block-device-operations.m4 b/config/kernel-bdev-block-device-operations.m4
index 28c3032aa..8b5e0a32b 100644
--- a/config/kernel-bdev-block-device-operations.m4
+++ b/config/kernel-bdev-block-device-operations.m4
@@ -7,24 +7,23 @@ AC_DEFUN([ZFS_AC_KERNEL_BDEV_BLOCK_DEVICE_OPERATIONS], [
 	EXTRA_KCFLAGS="${NO_UNUSED_BUT_SET_VARIABLE}"
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/blkdev.h>
-	],[
-		int (*blk_open) (struct block_device *, fmode_t) = NULL;
-		int (*blk_release) (struct gendisk *, fmode_t) = NULL;
-		int (*blk_ioctl) (struct block_device *, fmode_t,
-		                  unsigned, unsigned long) = NULL;
-		int (*blk_compat_ioctl) (struct block_device *, fmode_t,
-                                         unsigned, unsigned long) = NULL;
-		struct block_device_operations blk_ops = {
+
+		int blk_open(struct block_device *bdev, fmode_t mode)
+		    { return 0; }
+		int blk_release(struct gendisk *g, fmode_t mode) { return 0; }
+		int blk_ioctl(struct block_device *bdev, fmode_t mode,
+		    unsigned x, unsigned long y) { return 0; }
+		int blk_compat_ioctl(struct block_device * bdev, fmode_t mode,
+		    unsigned x, unsigned long y) { return 0; }
+
+		static const struct block_device_operations
+		    bops __attribute__ ((unused)) = {
 			.open		= blk_open,
 			.release	= blk_release,
 			.ioctl		= blk_ioctl,
 			.compat_ioctl	= blk_compat_ioctl,
 		};
-		
-		blk_ops.open(NULL, 0);
-		blk_ops.release(NULL, 0);
-		blk_ops.ioctl(NULL, 0, 0, 0);
-		blk_ops.compat_ioctl(NULL, 0, 0, 0);
+	],[
 	],[
 		AC_MSG_RESULT(struct block_device)
 		AC_DEFINE(HAVE_BDEV_BLOCK_DEVICE_OPERATIONS, 1,
diff --git a/config/kernel-bio-end-io-t-args.m4 b/config/kernel-bio-end-io-t-args.m4
index 44e4826bf..407e55cd0 100644
--- a/config/kernel-bio-end-io-t-args.m4
+++ b/config/kernel-bio-end-io-t-args.m4
@@ -11,11 +11,11 @@ AC_DEFUN([ZFS_AC_KERNEL_BIO_END_IO_T_ARGS], [
 	AC_MSG_CHECKING([whether bio_end_io_t wants 2 args])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/bio.h>
-	],[
-		void (*wanted_end_io)(struct bio *, int) = NULL;
-		bio_end_io_t *local_end_io __attribute__ ((unused));
 
-		local_end_io = wanted_end_io;
+		void wanted_end_io(struct bio *bio, int x) { return; }
+
+		bio_end_io_t *end_io __attribute__ ((unused)) = wanted_end_io;
+	],[
 	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_2ARGS_BIO_END_IO_T, 1,
diff --git a/config/kernel-create-nameidata.m4 b/config/kernel-create-nameidata.m4
index 100f07761..9aad46fec 100644
--- a/config/kernel-create-nameidata.m4
+++ b/config/kernel-create-nameidata.m4
@@ -5,18 +5,21 @@ AC_DEFUN([ZFS_AC_KERNEL_CREATE_NAMEIDATA], [
 	AC_MSG_CHECKING([whether iops->create() takes struct nameidata])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
+
 		#ifdef HAVE_MKDIR_UMODE_T
-		int (*inode_create) (struct inode *,struct dentry *,
-		                     umode_t, struct nameidata *) = NULL;
+		int inode_create(struct inode *inode ,struct dentry *dentry,
+		    umode_t umode, struct nameidata *nidata) { return 0; }
 		#else
-		int (*inode_create) (struct inode *,struct dentry *,
-		                     int, struct nameidata *) = NULL;
+		int inode_create(struct inode *inode,struct dentry *dentry,
+		    int umode, struct nameidata * nidata) { return 0; }
 		#endif
-		struct inode_operations iops __attribute__ ((unused)) = {
+
+		static const struct inode_operations
+		    iops __attribute__ ((unused)) = {
 			.create		= inode_create,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_CREATE_NAMEIDATA, 1,
 		          [iops->create() operation takes nameidata])
diff --git a/config/kernel-dentry-operations.m4 b/config/kernel-dentry-operations.m4
index dfbea7dfd..3182490c9 100644
--- a/config/kernel-dentry-operations.m4
+++ b/config/kernel-dentry-operations.m4
@@ -5,12 +5,16 @@ AC_DEFUN([ZFS_AC_KERNEL_D_REVALIDATE_NAMEIDATA], [
 	AC_MSG_CHECKING([whether dops->d_revalidate() takes struct nameidata])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/dcache.h>
-	],[
-		int (*revalidate) (struct dentry *, struct nameidata *) = NULL;
-		struct dentry_operations dops __attribute__ ((unused)) = {
-			.d_revalidate		= revalidate,
+
+		int revalidate (struct dentry *dentry,
+		    struct nameidata *nidata) { return 0; }
+
+		static const struct dentry_operations
+		    dops __attribute__ ((unused)) = {
+			.d_revalidate	= revalidate,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_D_REVALIDATE_NAMEIDATA, 1,
 		          [dops->d_revalidate() operation takes nameidata])
diff --git a/config/kernel-dirty-inode.m4 b/config/kernel-dirty-inode.m4
index 2ededf154..ffd87bb14 100644
--- a/config/kernel-dirty-inode.m4
+++ b/config/kernel-dirty-inode.m4
@@ -8,11 +8,14 @@ AC_DEFUN([ZFS_AC_KERNEL_DIRTY_INODE_WITH_FLAGS], [
 	AC_MSG_CHECKING([whether sops->dirty_inode() wants flags])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		void (*dirty_inode) (struct inode *, int) = NULL;
-		struct super_operations sops __attribute__ ((unused));
 
-		sops.dirty_inode = dirty_inode;
+		void dirty_inode(struct inode *a, int b) { return; }
+
+		static const struct super_operations
+		    sops __attribute__ ((unused)) = {
+			.dirty_inode = dirty_inode,
+		};
+	],[
 	],[
 		AC_MSG_RESULT([yes])
 		AC_DEFINE(HAVE_DIRTY_INODE_WITH_FLAGS, 1,
diff --git a/config/kernel-fallocate.m4 b/config/kernel-fallocate.m4
index 6ac5ae65c..550906472 100644
--- a/config/kernel-fallocate.m4
+++ b/config/kernel-fallocate.m4
@@ -5,12 +5,16 @@ AC_DEFUN([ZFS_AC_KERNEL_FILE_FALLOCATE], [
 	AC_MSG_CHECKING([whether fops->fallocate() exists])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		long (*fallocate) (struct file *, int, loff_t, loff_t) = NULL;
-		struct file_operations fops __attribute__ ((unused)) = {
-			.fallocate = fallocate,
+
+		long test_fallocate(struct file *file, int mode,
+		    loff_t offset, loff_t len) { return 0; }
+
+		static const struct file_operations
+		    fops __attribute__ ((unused)) = {
+			.fallocate = test_fallocate,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_FILE_FALLOCATE, 1, [fops->fallocate() exists])
 	],[
@@ -25,34 +29,18 @@ AC_DEFUN([ZFS_AC_KERNEL_INODE_FALLOCATE], [
 	AC_MSG_CHECKING([whether iops->fallocate() exists])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		long (*fallocate) (struct inode *, int, loff_t, loff_t) = NULL;
-		struct inode_operations fops __attribute__ ((unused)) = {
-			.fallocate = fallocate,
-		};
-	],[
-		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_INODE_FALLOCATE, 1, [fops->fallocate() exists])
-	],[
-		AC_MSG_RESULT(no)
-	])
-])
 
-dnl #
-dnl # PaX Linux 2.6.38 - 3.x API
-dnl #
-AC_DEFUN([ZFS_AC_PAX_KERNEL_FILE_FALLOCATE], [
-	AC_MSG_CHECKING([whether fops->fallocate() exists])
-	ZFS_LINUX_TRY_COMPILE([
-		#include <linux/fs.h>
-	],[
-		long (*fallocate) (struct file *, int, loff_t, loff_t) = NULL;
-		struct file_operations_no_const fops __attribute__ ((unused)) = {
-			.fallocate = fallocate,
+		long test_fallocate(struct inode *inode, int mode,
+		    loff_t offset, loff_t len) { return 0; }
+
+		static const struct inode_operations
+		    fops __attribute__ ((unused)) = {
+			.fallocate = test_fallocate,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
-		AC_DEFINE(HAVE_FILE_FALLOCATE, 1, [fops->fallocate() exists])
+		AC_DEFINE(HAVE_INODE_FALLOCATE, 1, [fops->fallocate() exists])
 	],[
 		AC_MSG_RESULT(no)
 	])
@@ -65,5 +53,4 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_FALLOCATE], [
 	ZFS_AC_KERNEL_FILE_FALLOCATE
 	ZFS_AC_KERNEL_INODE_FALLOCATE
-	ZFS_AC_PAX_KERNEL_FILE_FALLOCATE
 ])
diff --git a/config/kernel-fsync.m4 b/config/kernel-fsync.m4
index ca00d93be..e1f2d68b9 100644
--- a/config/kernel-fsync.m4
+++ b/config/kernel-fsync.m4
@@ -4,11 +4,15 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_FSYNC_WITH_DENTRY], [
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		int (*fsync) (struct file *, struct dentry *, int) = NULL;
-		struct file_operations fops __attribute__ ((unused));
 
-		fops.fsync = fsync;
+		int test_fsync(struct file *f, struct dentry *dentry, int x)
+		    { return 0; }
+
+		static const struct file_operations
+		    fops __attribute__ ((unused)) = {
+			.fsync = test_fsync,
+		};
+	],[
 	],[
 		AC_MSG_RESULT([dentry])
 		AC_DEFINE(HAVE_FSYNC_WITH_DENTRY, 1,
@@ -23,11 +27,14 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_FSYNC_WITHOUT_DENTRY], [
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		int (*fsync) (struct file *, int) = NULL;
-		struct file_operations fops __attribute__ ((unused));
 
-		fops.fsync = fsync;
+		int test_fsync(struct file *f, int x) { return 0; }
+
+		static const struct file_operations
+		    fops __attribute__ ((unused)) = {
+			.fsync = test_fsync,
+		};
+	],[
 	],[
 		AC_MSG_RESULT([no dentry])
 		AC_DEFINE(HAVE_FSYNC_WITHOUT_DENTRY, 1,
@@ -42,68 +49,15 @@ dnl #
 AC_DEFUN([ZFS_AC_KERNEL_FSYNC_RANGE], [
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		int (*fsync) (struct file *, loff_t, loff_t, int) = NULL;
-		struct file_operations fops __attribute__ ((unused));
-
-		fops.fsync = fsync;
-	],[
-		AC_MSG_RESULT([range])
-		AC_DEFINE(HAVE_FSYNC_RANGE, 1,
-			[fops->fsync() with range])
-	],[
-	])
-])
 
-dnl #
-dnl # PaX Linux 2.6.x - 2.6.34 API
-dnl #
-AC_DEFUN([ZFS_AC_PAX_KERNEL_FSYNC_WITH_DENTRY], [
-	ZFS_LINUX_TRY_COMPILE([
-		#include <linux/fs.h>
-	],[
-		int (*fsync) (struct file *, struct dentry *, int) = NULL;
-		file_operations_no_const fops __attribute__ ((unused));
+		int test_fsync(struct file *f, loff_t a, loff_t b, int c)
+		    { return 0; }
 
-		fops.fsync = fsync;
-	],[
-		AC_MSG_RESULT([dentry])
-		AC_DEFINE(HAVE_FSYNC_WITH_DENTRY, 1,
-			[fops->fsync() with dentry])
+		static const struct file_operations
+		    fops __attribute__ ((unused)) = {
+			.fsync = test_fsync,
+		};
 	],[
-	])
-])
-
-dnl #
-dnl # PaX Linux 2.6.35 - Linux 3.0 API
-dnl #
-AC_DEFUN([ZFS_AC_PAX_KERNEL_FSYNC_WITHOUT_DENTRY], [
-	ZFS_LINUX_TRY_COMPILE([
-		#include <linux/fs.h>
-	],[
-		int (*fsync) (struct file *, int) = NULL;
-		file_operations_no_const fops __attribute__ ((unused));
-
-		fops.fsync = fsync;
-	],[
-		AC_MSG_RESULT([no dentry])
-		AC_DEFINE(HAVE_FSYNC_WITHOUT_DENTRY, 1,
-			[fops->fsync() without dentry])
-	],[
-	])
-])
-
-dnl #
-dnl # PaX Linux 3.1 - 3.x API
-dnl #
-AC_DEFUN([ZFS_AC_PAX_KERNEL_FSYNC_RANGE], [
-	ZFS_LINUX_TRY_COMPILE([
-		#include <linux/fs.h>
-	],[
-		int (*fsync) (struct file *, loff_t, loff_t, int) = NULL;
-		file_operations_no_const fops __attribute__ ((unused));
-
-		fops.fsync = fsync;
 	],[
 		AC_MSG_RESULT([range])
 		AC_DEFINE(HAVE_FSYNC_RANGE, 1,
@@ -117,7 +71,4 @@ AC_DEFUN([ZFS_AC_KERNEL_FSYNC], [
 	ZFS_AC_KERNEL_FSYNC_WITH_DENTRY
 	ZFS_AC_KERNEL_FSYNC_WITHOUT_DENTRY
 	ZFS_AC_KERNEL_FSYNC_RANGE
-	ZFS_AC_PAX_KERNEL_FSYNC_WITH_DENTRY
-	ZFS_AC_PAX_KERNEL_FSYNC_WITHOUT_DENTRY
-	ZFS_AC_PAX_KERNEL_FSYNC_RANGE
 ])
diff --git a/config/kernel-lookup-nameidata.m4 b/config/kernel-lookup-nameidata.m4
index 5e30be433..645560398 100644
--- a/config/kernel-lookup-nameidata.m4
+++ b/config/kernel-lookup-nameidata.m4
@@ -5,13 +5,17 @@ AC_DEFUN([ZFS_AC_KERNEL_LOOKUP_NAMEIDATA], [
 	AC_MSG_CHECKING([whether iops->lookup() takes struct nameidata])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		struct dentry * (*inode_lookup) (struct inode *,struct dentry *,
-		                     struct nameidata *) = NULL;
-		struct inode_operations iops __attribute__ ((unused)) = {
-			.lookup		= inode_lookup,
+
+		struct dentry *inode_lookup(struct inode *inode,
+		    struct dentry *dentry, struct nameidata *nidata)
+		    { return NULL; }
+
+		static const struct inode_operations iops
+		    __attribute__ ((unused)) = {
+			.lookup	= inode_lookup,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_LOOKUP_NAMEIDATA, 1,
 		          [iops->lookup() operation takes nameidata])
diff --git a/config/kernel-mkdir-umode-t.m4 b/config/kernel-mkdir-umode-t.m4
index dd5d94ba9..634260b3c 100644
--- a/config/kernel-mkdir-umode-t.m4
+++ b/config/kernel-mkdir-umode-t.m4
@@ -10,12 +10,16 @@ AC_DEFUN([ZFS_AC_KERNEL_MKDIR_UMODE_T], [
 	AC_MSG_CHECKING([whether iops->create()/mkdir()/mknod() take umode_t])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		int (*mkdir) (struct inode *,struct dentry *,umode_t) = NULL;
-		struct inode_operations iops __attribute__ ((unused)) = {
+
+		int mkdir(struct inode *inode, struct dentry *dentry,
+		    umode_t umode) { return 0; }
+
+		static const struct inode_operations
+		    iops __attribute__ ((unused)) = {
 			.mkdir = mkdir,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_MKDIR_UMODE_T, 1,
 		    [iops->create()/mkdir()/mknod() take umode_t])
diff --git a/config/kernel-shrink.m4 b/config/kernel-shrink.m4
index ea748c974..479fb3a6e 100644
--- a/config/kernel-shrink.m4
+++ b/config/kernel-shrink.m4
@@ -8,15 +8,18 @@ AC_DEFUN([ZFS_AC_KERNEL_SHRINK], [
 	AC_MSG_CHECKING([whether super_block has s_shrink])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		int (*shrink)(struct shrinker *, struct shrink_control *sc)
-			__attribute__ ((unused)) = NULL;
-		struct super_block sb __attribute__ ((unused)) = {
+
+		int shrink(struct shrinker *s, struct shrink_control *sc)
+		    { return 0; }
+
+		static const struct super_block
+		    sb __attribute__ ((unused)) = {
 			.s_shrink.shrink = shrink,
 			.s_shrink.seeks = DEFAULT_SEEKS,
 			.s_shrink.batch = 0,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_SHRINK, 1, [struct super_block has s_shrink])
 
@@ -29,13 +32,15 @@ AC_DEFUN([ZFS_AC_KERNEL_NR_CACHED_OBJECTS], [
 	AC_MSG_CHECKING([whether sops->nr_cached_objects() exists])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		int (*nr_cached_objects)(struct super_block *)
-			__attribute__ ((unused)) = NULL;
-		struct super_operations sops __attribute__ ((unused)) = {
+
+		int nr_cached_objects(struct super_block *sb) { return 0; }
+
+		static const struct super_operations
+		    sops __attribute__ ((unused)) = {
 			.nr_cached_objects = nr_cached_objects,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_NR_CACHED_OBJECTS, 1,
 			[sops->nr_cached_objects() exists])
@@ -48,13 +53,16 @@ AC_DEFUN([ZFS_AC_KERNEL_FREE_CACHED_OBJECTS], [
 	AC_MSG_CHECKING([whether sops->free_cached_objects() exists])
 	ZFS_LINUX_TRY_COMPILE([
 		#include <linux/fs.h>
-	],[
-		void (*free_cached_objects)(struct super_block *, int)
-			__attribute__ ((unused)) = NULL;
-		struct super_operations sops __attribute__ ((unused)) = {
+
+		void free_cached_objects(struct super_block *sb, int x)
+		    { return; }
+
+		static const struct super_operations
+		    sops __attribute__ ((unused)) = {
 			.free_cached_objects = free_cached_objects,
 		};
 	],[
+	],[
 		AC_MSG_RESULT(yes)
 		AC_DEFINE(HAVE_FREE_CACHED_OBJECTS, 1,
 			[sops->free_cached_objects() exists])