From: Alexei Starovoitov <ast@kernel.org>
Date: Wed, 14 Jul 2021 17:54:15 -0700
Subject: bpf: Teach stack depth check about async callbacks.
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Patch-mainline: v5.15-rc1
Git-commit: 7ddc80a476c2d599246028af5808d15f9e24c109
References: jsc#PED-1377

Teach max stack depth checking algorithm about async callbacks
that don't increase bpf program stack size.
Also add sanity check that bpf_tail_call didn't sneak into async cb.
It's impossible, since PTR_TO_CTX is not available in async cb,
hence the program cannot contain bpf_tail_call(ctx,...);

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210715005417.78572-10-alexei.starovoitov@gmail.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 include/linux/bpf_verifier.h |    1 +
 kernel/bpf/verifier.c        |   18 +++++++++++++++---
 2 files changed, 16 insertions(+), 3 deletions(-)

--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -406,6 +406,7 @@ struct bpf_subprog_info {
 	bool has_tail_call;
 	bool tail_call_reachable;
 	bool has_ld_abs;
+	bool is_async_cb;
 };
 
 /* single container for all structs
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3685,6 +3685,8 @@ process_func:
 continue_func:
 	subprog_end = subprog[idx + 1].start;
 	for (; i < subprog_end; i++) {
+		int next_insn;
+
 		if (!bpf_pseudo_call(insn + i) && !bpf_pseudo_func(insn + i))
 			continue;
 		/* remember insn and function to return to */
@@ -3692,13 +3694,22 @@ continue_func:
 		ret_prog[frame] = idx;
 
 		/* find the callee */
-		i = i + insn[i].imm + 1;
-		idx = find_subprog(env, i);
+		next_insn = i + insn[i].imm + 1;
+		idx = find_subprog(env, next_insn);
 		if (idx < 0) {
 			WARN_ONCE(1, "verifier bug. No program starts at insn %d\n",
-				  i);
+				  next_insn);
 			return -EFAULT;
 		}
+		if (subprog[idx].is_async_cb) {
+			if (subprog[idx].has_tail_call) {
+				verbose(env, "verifier bug. subprog has tail_call and async cb\n");
+				return -EFAULT;
+			}
+			 /* async callbacks don't increase bpf prog stack size */
+			continue;
+		}
+		i = next_insn;
 
 		if (subprog[idx].has_tail_call)
 			tail_call_reachable = true;
@@ -5743,6 +5754,7 @@ static int __check_func_call(struct bpf_
 		struct bpf_verifier_state *async_cb;
 
 		/* there is no real recursion here. timer callbacks are async */
+		env->subprog_info[subprog].is_async_cb = true;
 		async_cb = push_async_cb(env, env->subprog_info[subprog].start,
 					 *insn_idx, subprog);
 		if (!async_cb)