linux-kernel - [PATCH bpf 2/2] bpf: Avoid using ARRAY

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Message-Id: <20210517092830.1026418-2-revest@chromium.org>
Date:   Mon, 17 May 2021 11:28:30 +0200
From:   Florent Revest <revest@...omium.org>
To:     bpf@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        kpsingh@...nel.org, jackmanb@...gle.com,
        linux-kernel@...r.kernel.org, Florent Revest <revest@...omium.org>,
        kernel test robot <lkp@...el.com>
Subject: [PATCH bpf 2/2] bpf: Avoid using ARRAY_SIZE on an uninitialized pointer

The cppcheck static code analysis reported the following error:
>> helpers.c:713:43: warning: Uninitialized variable: bufs [uninitvar]
    if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bufs->tmp_bufs))) {
                                             ^

ARRAY_SIZE is a macro that expands to sizeofs, so bufs is not actually
dereferenced at runtime, and the code is actually safe. But to keep
things tidy, this patch removes the need for a call to ARRAY_SIZE by
extracting the size of the array into a macro. Cppcheck should no longer
be confused and the code ends up being a bit cleaner.

Reported-by: kernel test robot <lkp@...el.com>
Signed-off-by: Florent Revest <revest@...omium.org>
---
 kernel/bpf/helpers.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 3a5ab614cbb0..73443498d88f 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -698,8 +698,9 @@ static int bpf_trace_copy_string(char *buf, void *unsafe_ptr, char fmt_ptype,
 #define MAX_BPRINTF_BUF_LEN	512
 
 /* Support executing three nested bprintf helper calls on a given CPU */
+#define MAX_BPRINTF_NEST_LEVEL	3
 struct bpf_bprintf_buffers {
-	char tmp_bufs[3][MAX_BPRINTF_BUF_LEN];
+	char tmp_bufs[MAX_BPRINTF_NEST_LEVEL][MAX_BPRINTF_BUF_LEN];
 };
 static DEFINE_PER_CPU(struct bpf_bprintf_buffers, bpf_bprintf_bufs);
 static DEFINE_PER_CPU(int, bpf_bprintf_nest_level);
@@ -711,7 +712,7 @@ static int try_get_fmt_tmp_buf(char **tmp_buf)
 
 	preempt_disable();
 	nest_level = this_cpu_inc_return(bpf_bprintf_nest_level);
-	if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bufs->tmp_bufs))) {
+	if (WARN_ON_ONCE(nest_level > MAX_BPRINTF_NEST_LEVEL)) {
 		this_cpu_dec(bpf_bprintf_nest_level);
 		preempt_enable();
 		return -EBUSY;
-- 
2.31.1.751.gd2f1c929bd-goog