From: David Vernet <void@manifault.com>
Date: Mon, 9 Oct 2023 11:14:13 -0500
Subject: bpf: Fix verifier log for async callback return values
Patch-mainline: v6.6-rc6
Git-commit: 829955981c557c7fc7416581c4cd68a8a0c28620
References: jsc#PED-6811

The verifier, as part of check_return_code(), verifies that async
callbacks such as from e.g. timers, will return 0. It does this by
correctly checking that R0->var_off is in tnum_const(0), which
effectively checks that it's in a range of 0. If this condition fails,
however, it prints an error message which says that the value should
have been in (0x0; 0x1). This results in possibly confusing output such
as the following in which an async callback returns 1:

  At async callback the register R0 has value (0x1; 0x0) should have been in (0x0; 0x1)

The fix is easy -- we should just pass the tnum_const(0) as the correct
range to verbose_invalid_scalar(), which will then print the following:

  At async callback the register R0 has value (0x1; 0x0) should have been in (0x0; 0x0)

Fixes: bfc6bb74e4f1 ("bpf: Implement verifier support for validation of async callbacks.")
Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20231009161414.235829-1-void@manifault.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 kernel/bpf/verifier.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -14478,7 +14478,7 @@ static int check_return_code(struct bpf_
 	struct tnum enforce_attach_type_range = tnum_unknown;
 	const struct bpf_prog *prog = env->prog;
 	struct bpf_reg_state *reg;
-	struct tnum range = tnum_range(0, 1);
+	struct tnum range = tnum_range(0, 1), const_0 = tnum_const(0);
 	enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
 	int err;
 	struct bpf_func_state *frame = env->cur_state->frame[0];
@@ -14526,8 +14526,8 @@ static int check_return_code(struct bpf_
 			return -EINVAL;
 		}
 
-		if (!tnum_in(tnum_const(0), reg->var_off)) {
-			verbose_invalid_scalar(env, reg, &range, "async callback", "R0");
+		if (!tnum_in(const_0, reg->var_off)) {
+			verbose_invalid_scalar(env, reg, &const_0, "async callback", "R0");
 			return -EINVAL;
 		}
 		return 0;