Merge branch 'Fix for crash due to overwrite in copy_map_value'

Kumar Kartikeya says:

====================

A fix for an oversight in copy_map_value that leads to kernel crash.

Also, a question for BPF developers:
It seems in arraymap.c, we always do check_and_free_timer_in_array after we do
copy_map_value in map_update_elem callback, but the same is not done for
hashtab.c. Is there a specific reason for this difference in behavior, or did I
miss that it happens for hashtab.c as well?

Changlog:
---------
v1 -> v2:
v1: https://lore.kernel.org/bpf/20220209051113.870717-1-memxor@gmail.com

 * Fix build error for selftests patch due to missing SYS_PREFIX in bpf tree
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf.h

@@ -224,7 +224,8 @@ static inline void copy_map_value(struct bpf_map *map, void *dst, void *src)
 	if (unlikely(map_value_has_spin_lock(map))) {
 		s_off = map->spin_lock_off;
 		s_sz = sizeof(struct bpf_spin_lock);
-	} else if (unlikely(map_value_has_timer(map))) {
+	}
+	if (unlikely(map_value_has_timer(map))) {
 		t_off = map->timer_off;
 		t_sz = sizeof(struct bpf_timer);
 	}

tools/testing/selftests/bpf/prog_tests/timer_crash.c

+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include "timer_crash.skel.h"
+
+enum {
+	MODE_ARRAY,
+	MODE_HASH,
+};
+
+static void test_timer_crash_mode(int mode)
+{
+	struct timer_crash *skel;
+
+	skel = timer_crash__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "timer_crash__open_and_load"))
+		return;
+	skel->bss->pid = getpid();
+	skel->bss->crash_map = mode;
+	if (!ASSERT_OK(timer_crash__attach(skel), "timer_crash__attach"))
+		goto end;
+	usleep(1);
+end:
+	timer_crash__destroy(skel);
+}
+
+void test_timer_crash(void)
+{
+	if (test__start_subtest("array"))
+		test_timer_crash_mode(MODE_ARRAY);
+	if (test__start_subtest("hash"))
+		test_timer_crash_mode(MODE_HASH);
+}

tools/testing/selftests/bpf/progs/timer_crash.c

+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+
+struct map_elem {
+	struct bpf_timer timer;
+	struct bpf_spin_lock lock;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct map_elem);
+} amap SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct map_elem);
+} hmap SEC(".maps");
+
+int pid = 0;
+int crash_map = 0; /* 0 for amap, 1 for hmap */
+
+SEC("fentry/do_nanosleep")
+int sys_enter(void *ctx)
+{
+	struct map_elem *e, value = {};
+	void *map = crash_map ? (void *)&hmap : (void *)&amap;
+
+	if (bpf_get_current_task_btf()->tgid != pid)
+		return 0;
+
+	*(void **)&value = (void *)0xdeadcaf3;
+
+	bpf_map_update_elem(map, &(int){0}, &value, 0);
+	/* For array map, doing bpf_map_update_elem will do a
+	 * check_and_free_timer_in_array, which will trigger the crash if timer
+	 * pointer was overwritten, for hmap we need to use bpf_timer_cancel.
+	 */
+	if (crash_map == 1) {
+		e = bpf_map_lookup_elem(map, &(int){0});
+		if (!e)
+			return 0;
+		bpf_timer_cancel(&e->timer);
+	}
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";