[PATCH bpf-next v2] libbpf: Fix strncat bounds error in libbpf_prog_type_by_name

[PATCH bpf-next v2] libbpf: Fix strncat bounds error in libbpf_prog_type_by_name

[KP Singh]

From: KP Singh <kpsingh@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 <kpsingh@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 290684b504b7..dc7d493a7d3d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4693,7 +4693,7 @@ 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) - sizeof("btf_trace_"));
 			ret = btf__find_by_name(btf, raw_tp_btf_name);
 			btf__free(btf);
 			if (ret <= 0) {
-- 
2.20.1

Re: [PATCH bpf-next v2] libbpf: Fix strncat bounds error in libbpf_prog_type_by_name

[Alexei Starovoitov]

On Wed, Oct 23, 2019 at 8:40 AM KP Singh <kpsingh@chromium.org> wrote:
>
> From: KP Singh <kpsingh@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 <kpsingh@google.com>

Applied. Thanks

Re: [PATCH bpf-next v2] libbpf: Fix strncat bounds error in libbpf_prog_type_by_name

[Andrii Nakryiko]

On Wed, Oct 23, 2019 at 9:06 PM KP Singh <kpsingh@chromium.org> wrote:
>
> From: KP Singh <kpsingh@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 <kpsingh@google.com>
> ---

Acked-by: Andrii Nakryiko <andriin@fb.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 290684b504b7..dc7d493a7d3d 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4693,7 +4693,7 @@ 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) - sizeof("btf_trace_"));
>                         ret = btf__find_by_name(btf, raw_tp_btf_name);
>                         btf__free(btf);
>                         if (ret <= 0) {
> --
> 2.20.1
>