selftests: splice: Adjust for handler fallback removal

Some pseudo-filesystems do not have an explicit splice fops since adding
commit 36e2c7421f ("fs: don't allow splice read/write without explicit ops"),
and now will reject attempts to use splice() in those filesystem paths.

Reported-by: kernel test robot <rong.a.chen@intel.com>
Link: https://lore.kernel.org/lkml/202009181443.C2179FB@keescook/
Fixes: 36e2c7421f ("fs: don't allow splice read/write without explicit ops")
Cc: Christoph Hellwig <hch@lst.de>
Cc: Shuah Khan <shuah@kernel.org>
Cc: linux-kselftest@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/splice/short_splice_read.sh

@@ -1,21 +1,87 @@
 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0
+#
+# Test for mishandling of splice() on pseudofilesystems, which should catch
+# bugs like 11990a5bd7e5 ("module: Correctly truncate sysfs sections output")
+#
+# Since splice fallback was removed as part of the set_fs() rework, many of these
+# tests expect to fail now. See https://lore.kernel.org/lkml/202009181443.C2179FB@keescook/
 set -e
 
+DIR=$(dirname "$0")
+
 ret=0
 
+expect_success()
+{
+	title="$1"
+	shift
+
+	echo "" >&2
+	echo "$title ..." >&2
+
+	set +e
+	"$@"
+	rc=$?
+	set -e
+
+	case "$rc" in
+	0)
+		echo "ok: $title succeeded" >&2
+		;;
+	1)
+		echo "FAIL: $title should work" >&2
+		ret=$(( ret + 1 ))
+		;;
+	*)
+		echo "FAIL: something else went wrong" >&2
+		ret=$(( ret + 1 ))
+		;;
+	esac
+}
+
+expect_failure()
+{
+	title="$1"
+	shift
+
+	echo "" >&2
+	echo "$title ..." >&2
+
+	set +e
+	"$@"
+	rc=$?
+	set -e
+
+	case "$rc" in
+	0)
+		echo "FAIL: $title unexpectedly worked" >&2
+		ret=$(( ret + 1 ))
+		;;
+	1)
+		echo "ok: $title correctly failed" >&2
+		;;
+	*)
+		echo "FAIL: something else went wrong" >&2
+		ret=$(( ret + 1 ))
+		;;
+	esac
+}
+
 do_splice()
 {
 	filename="$1"
 	bytes="$2"
 	expected="$3"
+	report="$4"
 
-	out=$(./splice_read "$filename" "$bytes" | cat)
+	out=$("$DIR"/splice_read "$filename" "$bytes" | cat)
 	if [ "$out" = "$expected" ] ; then
-		echo "ok: $filename $bytes"
+		echo "      matched $report" >&2
+		return 0
 	else
-		echo "FAIL: $filename $bytes"
-		ret=1
+		echo "      no match: '$out' vs $report" >&2
+		return 1
 	fi
 }
 
@@ -23,34 +89,45 @@ test_splice()
 {
 	filename="$1"
 
+	echo "  checking $filename ..." >&2
+
 	full=$(cat "$filename")
+	rc=$?
+	if [ $rc -ne 0 ] ; then
+		return 2
+	fi
+
 	two=$(echo "$full" | grep -m1 . | cut -c-2)
 
 	# Make sure full splice has the same contents as a standard read.
-	do_splice "$filename" 4096 "$full"
+	echo "    splicing 4096 bytes ..." >&2
+	if ! do_splice "$filename" 4096 "$full" "full read" ; then
+		return 1
+	fi
 
 	# Make sure a partial splice see the first two characters.
-	do_splice "$filename" 2 "$two"
+	echo "    splicing 2 bytes ..." >&2
+	if ! do_splice "$filename" 2 "$two" "'$two'" ; then
+		return 1
+	fi
+
+	return 0
 }
 
-# proc_single_open(), seq_read()
-test_splice /proc/$$/limits
-# special open, seq_read()
-test_splice /proc/$$/comm
+### /proc/$pid/ has no splice interface; these should all fail.
+expect_failure "proc_single_open(), seq_read() splice" test_splice /proc/$$/limits
+expect_failure "special open(), seq_read() splice" test_splice /proc/$$/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
+### /proc/sys/ has a splice interface; these should all succeed.
+expect_success "proc_handler: proc_dointvec_minmax() splice" test_splice /proc/sys/fs/nr_open
+expect_success "proc_handler: proc_dostring() splice" test_splice /proc/sys/kernel/modprobe
+expect_success "proc_handler: special read splice" test_splice /proc/sys/kernel/version
 
+### /sys/ has no splice interface; these should all fail.
 if ! [ -d /sys/module/test_module/sections ] ; then
-	modprobe test_module
+	expect_success "test_module kernel module load" modprobe test_module
 fi
-# kernfs, attr
-test_splice /sys/module/test_module/coresize
-# kernfs, binattr
-test_splice /sys/module/test_module/sections/.init.text
+expect_failure "kernfs attr splice" test_splice /sys/module/test_module/coresize
+expect_failure "kernfs binattr splice" test_splice /sys/module/test_module/sections/.init.text
 
 exit $ret