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From:   Yuntao Wang <ytcoode@gmail.com>
To:     bpf@vger.kernel.org
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Yuntao Wang <ytcoode@gmail.com>
Subject: [PATCH bpf-next] libbpf: Add a check to ensure that page_cnt is non-zero
Date:   Wed,  2 Mar 2022 00:57:37 +0800
Message-Id: <20220301165737.672007-1-ytcoode@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The page_cnt parameter is used to specify the number of memory pages
allocated for each per-CPU buffer, it must be non-zero and a power of 2.

Currently, the __perf_buffer__new() function attempts to validate that
the page_cnt is a power of 2 but forgets checking for the case where
page_cnt is zero, we can fix it by replacing 'page_cnt & (page_cnt - 1)'
with '!is_power_of_2(page_cnt)'.

Thus we also don't need to add a check in perf_buffer__new_v0_6_0() to
make sure that page_cnt is non-zero and the check for zero in
perf_buffer__new_raw_v0_6_0() can also be removed.

The code is cleaner and more readable.

Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
---
 tools/lib/bpf/libbpf.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index be6480e260c4..4dd1d82cd5b9 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -33,6 +33,7 @@
 #include <linux/filter.h>
 #include <linux/list.h>
 #include <linux/limits.h>
+#include <linux/log2.h>
 #include <linux/perf_event.h>
 #include <linux/ring_buffer.h>
 #include <linux/version.h>
@@ -10951,7 +10952,7 @@ struct perf_buffer *perf_buffer__new_raw_v0_6_0(int map_fd, size_t page_cnt,
 {
 	struct perf_buffer_params p = {};
 
-	if (page_cnt == 0 || !attr)
+	if (!attr)
 		return libbpf_err_ptr(-EINVAL);
 
 	if (!OPTS_VALID(opts, perf_buffer_raw_opts))
@@ -10992,7 +10993,7 @@ static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
 	__u32 map_info_len;
 	int err, i, j, n;
 
-	if (page_cnt & (page_cnt - 1)) {
+	if (!is_power_of_2(page_cnt)) {
 		pr_warn("page count should be power of two, but is %zu\n",
 			page_cnt);
 		return ERR_PTR(-EINVAL);
-- 
2.35.1