linux-kernel - [PATCH] bpf/btf: Fix is_int

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Date:   Wed, 12 Oct 2022 20:58:15 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     martin.lau@...ux.dev, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: [PATCH] bpf/btf: Fix is_int_ptr()

When tracing a kernel function with arg type is u32*, btf_ctx_access()
would report error: arg2 type INT is not a struct.

The commit bb6728d75611 ("bpf: Allow access to int pointer arguments
in tracing programs") added support for int pointer, but don't skip
modifiers before checking it's type. This patch fixes it.

Fixes: bb6728d75611 ("bpf: Allow access to int pointer arguments in tracing programs")
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 kernel/bpf/btf.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index eba603cec2c5..2b343c42ed10 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5316,8 +5316,8 @@ static bool is_int_ptr(struct btf *btf, const struct btf_type *t)
 	/* t comes in already as a pointer */
 	t = btf_type_by_id(btf, t->type);
 
-	/* allow const */
-	if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
+	/* skip modifiers */
+	while (btf_type_is_modifier(t))
 		t = btf_type_by_id(btf, t->type);
 
 	return btf_type_is_int(t);
-- 
2.37.2