selftests: splice: Check behavior of full and short splices

In order to help catch regressions in splice vs read behavior in certain
special files, test a few with various different kinds of internal
kernel helpers.

Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

tools/testing/selftests/splice/.gitignore

 # SPDX-License-Identifier: GPL-2.0-only
 default_file_splice_read
+splice_read

tools/testing/selftests/splice/Makefile

 # SPDX-License-Identifier: GPL-2.0
-TEST_PROGS := default_file_splice_read.sh
-TEST_GEN_PROGS_EXTENDED := default_file_splice_read
+TEST_PROGS := default_file_splice_read.sh short_splice_read.sh
+TEST_GEN_PROGS_EXTENDED := default_file_splice_read splice_read
 
 include ../lib.mk

tools/testing/selftests/splice/config

+CONFIG_TEST_LKM=m

tools/testing/selftests/splice/settings

+timeout=5

tools/testing/selftests/splice/short_splice_read.sh

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+set -e
+
+ret=0
+
+do_splice()
+{
+	filename="$1"
+	bytes="$2"
+	expected="$3"
+
+	out=$(./splice_read "$filename" "$bytes" | cat)
+	if [ "$out" = "$expected" ] ; then
+		echo "ok: $filename $bytes"
+	else
+		echo "FAIL: $filename $bytes"
+		ret=1
+	fi
+}
+
+test_splice()
+{
+	filename="$1"
+
+	full=$(cat "$filename")
+	two=$(echo "$full" | grep -m1 . | cut -c-2)
+
+	# Make sure full splice has the same contents as a standard read.
+	do_splice "$filename" 4096 "$full"
+
+	# Make sure a partial splice see the first two characters.
+	do_splice "$filename" 2 "$two"
+}
+
+# proc_single_open(), seq_read()
+test_splice /proc/$$/limits
+# special open, seq_read()
+test_splice /proc/$$/comm
+
+# proc_handler, proc_dointvec_minmax
+test_splice /proc/sys/fs/nr_open
+# proc_handler, proc_dostring
+test_splice /proc/sys/kernel/modprobe
+# proc_handler, special read
+test_splice /proc/sys/kernel/version
+
+if ! [ -d /sys/module/test_module/sections ] ; then
+	modprobe test_module
+fi
+# kernfs, attr
+test_splice /sys/module/test_module/coresize
+# kernfs, binattr
+test_splice /sys/module/test_module/sections/.init.text
+
+exit $ret

tools/testing/selftests/splice/splice_read.c

+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+int main(int argc, char *argv[])
+{
+	int fd;
+	size_t size;
+	ssize_t spliced;
+
+	if (argc < 2) {
+		fprintf(stderr, "Usage: %s INPUT [BYTES]\n", argv[0]);
+		return EXIT_FAILURE;
+	}
+
+	fd = open(argv[1], O_RDONLY);
+	if (fd < 0) {
+		perror(argv[1]);
+		return EXIT_FAILURE;
+	}
+
+	if (argc == 3)
+		size = atol(argv[2]);
+	else {
+		struct stat statbuf;
+
+		if (fstat(fd, &statbuf) < 0) {
+			perror(argv[1]);
+			return EXIT_FAILURE;
+		}
+
+		if (statbuf.st_size > INT_MAX) {
+			fprintf(stderr, "%s: Too big\n", argv[1]);
+			return EXIT_FAILURE;
+		}
+
+		size = statbuf.st_size;
+	}
+
+	/* splice(2) file to stdout. */
+	spliced = splice(fd, NULL, STDOUT_FILENO, NULL,
+		      size, SPLICE_F_MOVE);
+	if (spliced < 0) {
+		perror("splice");
+		return EXIT_FAILURE;
+	}
+
+	close(fd);
+	return EXIT_SUCCESS;
+}