2022-03-13 11:25:24

by Yuntao Wang

Subject: [PATCH bpf-next] libbpf: Remove redundant check in btf_ext__new()

Since 'core_relo_len' is the last field of 'struct btf_ext_header', if
'xxx->hdr_len' is not less than 'offsetofend(xxx, core_relo_len)', then
'xxx->hdr_len' must also be not less than 'offsetofend(xxx, line_info_len)'.

We can check 'xxx->hdr_len < offsetofend(xxx, core_relo_len)' first, if it
passes, the 'xxx->hdr_len < offsetofend(xxx, line_info_len)' check will be
redundant, it can be removed.

Signed-off-by: Yuntao Wang <[email protected]>
---
tools/lib/bpf/btf.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 1383e26c5d1f..d55b44124c3e 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -2813,7 +2813,7 @@ struct btf_ext *btf_ext__new(const __u8 *data, __u32 size)
if (err)
goto done;

- if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, line_info_len)) {
+ if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len)) {
err = -EINVAL;
goto done;
}
@@ -2826,11 +2826,6 @@ struct btf_ext *btf_ext__new(const __u8 *data, __u32 size)
if (err)
goto done;

- if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len)) {
- err = -EINVAL;
- goto done;
- }
-
err = btf_ext_setup_core_relos(btf_ext);
if (err)
goto done;
--
2.35.1

2022-03-17 03:55:47

by Andrii Nakryiko

Subject: Re: [PATCH bpf-next] libbpf: Remove redundant check in btf_ext__new()

On Sat, Mar 12, 2022 at 9:14 AM Yuntao Wang <[email protected]> wrote:
>
> Since 'core_relo_len' is the last field of 'struct btf_ext_header', if
> 'xxx->hdr_len' is not less than 'offsetofend(xxx, core_relo_len)', then
> 'xxx->hdr_len' must also be not less than 'offsetofend(xxx, line_info_len)'.
>
> We can check 'xxx->hdr_len < offsetofend(xxx, core_relo_len)' first, if it
> passes, the 'xxx->hdr_len < offsetofend(xxx, line_info_len)' check will be
> redundant, it can be removed.
>
> Signed-off-by: Yuntao Wang <[email protected]>
> ---
> tools/lib/bpf/btf.c | 7 +------
> 1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 1383e26c5d1f..d55b44124c3e 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -2813,7 +2813,7 @@ struct btf_ext *btf_ext__new(const __u8 *data, __u32 size)
> if (err)
> goto done;
>
> - if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, line_info_len)) {
> + if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len)) {
> err = -EINVAL;
> goto done;
> }
> @@ -2826,11 +2826,6 @@ struct btf_ext *btf_ext__new(const __u8 *data, __u32 size)
> if (err)
> goto done;
>
> - if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len)) {
> - err = -EINVAL;
> - goto done;
> - }

it seems like it's actually a bug. If header is smaller then core
relos parsing should be skipped, I think. Maybe let's fix that
instead?

basically the logic should be:

1. if size of header is exactly == offsetof(core_relo_off) then skip core relos
2. otherwise check that it has enough size to cover core_relo_off and
core_relo_len, and error out if not
3. otherwise proceed to parsing core relos

> -
> err = btf_ext_setup_core_relos(btf_ext);
> if (err)
> goto done;
> --
> 2.35.1
>

2022-03-17 04:27:55

by Yuntao Wang

Subject: [PATCH bpf-next v2] libbpf: Don't return -EINVAL if hdr_len < offsetofend(core_relo_len)

Since core relos is an optional part of the .BTF.ext ELF section, we should
skip parsing it instead of returning -EINVAL if header size is less than
offsetofend(struct btf_ext_header, core_relo_len).

Fixes: e9fc3ce99b34 ("libbpf: Streamline error reporting for high-level APIs")
Signed-off-by: Yuntao Wang <[email protected]>
---
v1 -> v2: skip core relos if hdr_len < offsetofend(core_relo_len)

tools/lib/bpf/btf.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 1383e26c5d1f..9b7196b21498 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -2826,10 +2826,8 @@ struct btf_ext *btf_ext__new(const __u8 *data, __u32 size)
if (err)
goto done;

- if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len)) {
- err = -EINVAL;
- goto done;
- }
+ if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len))
+ goto done; // skip core relos parsing

err = btf_ext_setup_core_relos(btf_ext);
if (err)
--
2.35.1

2022-04-05 02:25:33

by Andrii Nakryiko

Subject: Re: [PATCH bpf-next v2] libbpf: Don't return -EINVAL if hdr_len < offsetofend(core_relo_len)

On Wed, Mar 16, 2022 at 7:52 AM Yuntao Wang <[email protected]> wrote:
>
> Since core relos is an optional part of the .BTF.ext ELF section, we should
> skip parsing it instead of returning -EINVAL if header size is less than
> offsetofend(struct btf_ext_header, core_relo_len).
>
> Fixes: e9fc3ce99b34 ("libbpf: Streamline error reporting for high-level APIs")
> Signed-off-by: Yuntao Wang <[email protected]>
> ---
> v1 -> v2: skip core relos if hdr_len < offsetofend(core_relo_len)
>

Seems like this never made it to Patchworks. Can you please trim down
the CC list and resubmit?

> tools/lib/bpf/btf.c | 6 ++----
> 1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 1383e26c5d1f..9b7196b21498 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -2826,10 +2826,8 @@ struct btf_ext *btf_ext__new(const __u8 *data, __u32 size)
> if (err)
> goto done;
>
> - if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len)) {
> - err = -EINVAL;
> - goto done;
> - }
> + if (btf_ext->hdr->hdr_len < offsetofend(struct btf_ext_header, core_relo_len))
> + goto done; // skip core relos parsing

don't use C++-style comments, only /* */

>
> err = btf_ext_setup_core_relos(btf_ext);
> if (err)
> --
> 2.35.1
>