linux-kernel - [PATCH bpf-next] libbpf: Fix strncat bounds error in libbpf_prog_type_by

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Message-Id: <20191022141833.5706-1-kpsingh@chromium.org>
Date:   Tue, 22 Oct 2019 16:18:33 +0200
From:   KP Singh <kpsingh@...omium.org>
To:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Florent Revest <revest@...omium.org>
Subject: [PATCH bpf-next] libbpf: Fix strncat bounds error in libbpf_prog_type_by_name

From: KP Singh <kpsingh@...gle.com>

On compiling samples with this change, one gets an error:

 error: ‘strncat’ specified bound 118 equals destination size
  [-Werror=stringop-truncation]

    strncat(dst, name + section_names[i].len,
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     sizeof(raw_tp_btf_name) - (dst - raw_tp_btf_name));
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

strncat requires the destination to have enough space for the
terminating null byte.

Fixes: f75a697e09137 ("libbpf: Auto-detect btf_id of BTF-based raw_tracepoint")
Signed-off-by: KP Singh <kpsingh@...gle.com>
---
 tools/lib/bpf/libbpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 9364e66d755d..5fff3f15d705 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4666,7 +4666,7 @@ int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
 			}
 			/* prepend "btf_trace_" prefix per kernel convention */
 			strncat(dst, name + section_names[i].len,
-				sizeof(raw_tp_btf_name) - (dst - raw_tp_btf_name));
+				sizeof(raw_tp_btf_name) - (dst - raw_tp_btf_name + 1));
 			ret = btf__find_by_name(btf, raw_tp_btf_name);
 			btf__free(btf);
 			if (ret <= 0) {
-- 
2.20.1