[PATCH bpf-next] libbpf: Fix strncat bounds error in libbpf_prog_type_by_name

[KP Singh]

From: KP Singh <kpsi...@google.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 <kpsi...@google.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