selftests/bpf: Add test for bpf_timer overwriting crash

Add a test that validates that timer value is not overwritten when doing
a copy_map_value call in the kernel. Without the prior fix, this test
triggers a crash.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220209070324.1093182-3-memxor@gmail.com

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

@@ -0,0 +1,32 @@
+// 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

@@ -0,0 +1,54 @@
+// 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";