Merge branch 'Fix for check_max_stack_depth'

Kumar Kartikeya Dwivedi says:

====================
Fix for a bug in check_max_stack_depth which allows bypassing the
512-byte stack limit.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Alexei Starovoitov

kernel/bpf/verifier.c

@@ -5642,8 +5642,9 @@ static int check_max_stack_depth(struct bpf_verifier_env *env)
 				verbose(env, "verifier bug. subprog has tail_call and async cb\n");
 				return -EFAULT;
 			}
-			 /* async callbacks don't increase bpf prog stack size */
-			continue;
+			/* async callbacks don't increase bpf prog stack size unless called directly */
+			if (!bpf_pseudo_call(insn + i))
+				continue;
 		}
 		i = next_insn;
 

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

@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+
+#include "async_stack_depth.skel.h"
+
+void test_async_stack_depth(void)
+{
+	RUN_TESTS(async_stack_depth);
+}

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

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+#include "bpf_misc.h"
+
+struct hmap_elem {
+	struct bpf_timer timer;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 64);
+	__type(key, int);
+	__type(value, struct hmap_elem);
+} hmap SEC(".maps");
+
+__attribute__((noinline))
+static int timer_cb(void *map, int *key, struct bpf_timer *timer)
+{
+	volatile char buf[256] = {};
+	return buf[69];
+}
+
+SEC("tc")
+__failure __msg("combined stack size of 2 calls")
+int prog(struct __sk_buff *ctx)
+{
+	struct hmap_elem *elem;
+	volatile char buf[256] = {};
+
+	elem = bpf_map_lookup_elem(&hmap, &(int){0});
+	if (!elem)
+		return 0;
+
+	timer_cb(NULL, NULL, NULL);
+	return bpf_timer_set_callback(&elem->timer, timer_cb) + buf[0];
+}
+
+char _license[] SEC("license") = "GPL";