linux-kernel - [PATCH] bpftool: Fix undefined behavior caused by shifting into the sign bit

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Message-Id: <20240908140009.3149781-1-visitorckw@gmail.com>
Date: Sun,  8 Sep 2024 22:00:09 +0800
From: Kuan-Wei Chiu <visitorckw@...il.com>
To: qmo@...nel.org
Cc: ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	jserv@...s.ncku.edu.tw,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Kuan-Wei Chiu <visitorckw@...il.com>
Subject: [PATCH] bpftool: Fix undefined behavior caused by shifting into the sign bit

Replace shifts of '1' with '1U' in bitwise operations within
__show_dev_tc_bpf() to prevent undefined behavior caused by shifting
into the sign bit of a signed integer. By using '1U', the operations
are explicitly performed on unsigned integers, avoiding potential
integer overflow or sign-related issues.

Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
---
 tools/bpf/bpftool/net.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/net.c b/tools/bpf/bpftool/net.c
index 968714b4c3d4..ad2ea6cf2db1 100644
--- a/tools/bpf/bpftool/net.c
+++ b/tools/bpf/bpftool/net.c
@@ -482,9 +482,9 @@ static void __show_dev_tc_bpf(const struct ip_devname_ifindex *dev,
 		if (prog_flags[i] || json_output) {
 			NET_START_ARRAY("prog_flags", "%s ");
 			for (j = 0; prog_flags[i] && j < 32; j++) {
-				if (!(prog_flags[i] & (1 << j)))
+				if (!(prog_flags[i] & (1U << j)))
 					continue;
-				NET_DUMP_UINT_ONLY(1 << j);
+				NET_DUMP_UINT_ONLY(1U << j);
 			}
 			NET_END_ARRAY("");
 		}
@@ -493,9 +493,9 @@ static void __show_dev_tc_bpf(const struct ip_devname_ifindex *dev,
 			if (link_flags[i] || json_output) {
 				NET_START_ARRAY("link_flags", "%s ");
 				for (j = 0; link_flags[i] && j < 32; j++) {
-					if (!(link_flags[i] & (1 << j)))
+					if (!(link_flags[i] & (1U << j)))
 						continue;
-					NET_DUMP_UINT_ONLY(1 << j);
+					NET_DUMP_UINT_ONLY(1U << j);
 				}
 				NET_END_ARRAY("");
 			}
-- 
2.34.1