linux-kernel - [PATCH AUTOSEL 5.10 108/114] bpftool: Fix readlink usage in get_fd

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Message-Id: <20250505231817.2697367-108-sashal@kernel.org>
Date: Mon,  5 May 2025 19:18:11 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Viktor Malik <vmalik@...hat.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Quentin Monnet <qmo@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	daniel@...earbox.net,
	bpf@...r.kernel.org
Subject: [PATCH AUTOSEL 5.10 108/114] bpftool: Fix readlink usage in get_fd_type

From: Viktor Malik <vmalik@...hat.com>

[ Upstream commit 0053f7d39d491b6138d7c526876d13885cbb65f1 ]

The `readlink(path, buf, sizeof(buf))` call reads at most sizeof(buf)
bytes and *does not* append null-terminator to buf. With respect to
that, fix two pieces in get_fd_type:

1. Change the truncation check to contain sizeof(buf) rather than
   sizeof(path).
2. Append null-terminator to buf.

Reported by Coverity.

Signed-off-by: Viktor Malik <vmalik@...hat.com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Reviewed-by: Quentin Monnet <qmo@...nel.org>
Link: https://lore.kernel.org/bpf/20250129071857.75182-1-vmalik@redhat.com
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/bpf/bpftool/common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
index eefa2b34e641a..33065b17900fa 100644
--- a/tools/bpf/bpftool/common.c
+++ b/tools/bpf/bpftool/common.c
@@ -311,10 +311,11 @@ int get_fd_type(int fd)
 		p_err("can't read link type: %s", strerror(errno));
 		return -1;
 	}
-	if (n == sizeof(path)) {
+	if (n == sizeof(buf)) {
 		p_err("can't read link type: path too long!");
 		return -1;
 	}
+	buf[n] = '\0';
 
 	if (strstr(buf, "bpf-map"))
 		return BPF_OBJ_MAP;
-- 
2.39.5