diff mbox series

[bpf-next] Revert "libbpf: make uniform use of btf__fd() accessor inside libbpf"

Message ID 20240313172345.75270-1-quentin@isovalent.com (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series [bpf-next] Revert "libbpf: make uniform use of btf__fd() accessor inside libbpf" | expand

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Commit Message

Quentin Monnet March 13, 2024, 5:23 p.m. UTC 
This reverts commit df7c3f7d3a3ddab31ca8cfa9b86a8729ec43fd2e.

There's no guarantee that obj->btf is non-NULL when passing it to
btf__fd(), and this function doesn't perform any check before
dereferencing its argument. As a consequence, this commit caused
segmentation faults in bpftool (for example) when trying to load
programs that come without BTF info.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
---
 tools/lib/bpf/libbpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Andrii Nakryiko March 13, 2024, 5:39 p.m. UTC | #1 
On Wed, Mar 13, 2024 at 10:24 AM Quentin Monnet <quentin@isovalent.com> wrote:
>
> This reverts commit df7c3f7d3a3ddab31ca8cfa9b86a8729ec43fd2e.
>
> There's no guarantee that obj->btf is non-NULL when passing it to
> btf__fd(), and this function doesn't perform any check before
> dereferencing its argument. As a consequence, this commit caused
> segmentation faults in bpftool (for example) when trying to load
> programs that come without BTF info.
>
> Signed-off-by: Quentin Monnet <quentin@isovalent.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 efab29b8935b..0f9a4d232468 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7343,7 +7343,7 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
>         load_attr.prog_ifindex = prog->prog_ifindex;
>
>         /* specify func_info/line_info only if kernel supports them */
> -       btf_fd = btf__fd(obj->btf);
> +       btf_fd = bpf_object__btf_fd(obj);

oh, my bad, sorry about that. But I'd still like to stick to using
btf__fd(), so maybe let's fix forward by dropping btf_fd variable here
and doing what bpf_object__create_map() does:

if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(...)) {
    load_attr.prog_btf_fd = btf__fd(obj->btf);
    ...
}

?

>         if (btf_fd >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
>                 load_attr.prog_btf_fd = btf_fd;
>                 load_attr.func_info = prog->func_info;
> --
> 2.34.1
>
Quentin Monnet March 13, 2024, 9:02 p.m. UTC | #2 
On 13 March 2024 17:39:14 GMT, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>On Wed, Mar 13, 2024 at 10:24 AM Quentin Monnet <quentin@isovalent.com> wrote:
>>
>> This reverts commit df7c3f7d3a3ddab31ca8cfa9b86a8729ec43fd2e.
>>
>> There's no guarantee that obj->btf is non-NULL when passing it to
>> btf__fd(), and this function doesn't perform any check before
>> dereferencing its argument. As a consequence, this commit caused
>> segmentation faults in bpftool (for example) when trying to load
>> programs that come without BTF info.
>>
>> Signed-off-by: Quentin Monnet <quentin@isovalent.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 efab29b8935b..0f9a4d232468 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -7343,7 +7343,7 @@ static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
>>         load_attr.prog_ifindex = prog->prog_ifindex;
>>
>>         /* specify func_info/line_info only if kernel supports them */
>> -       btf_fd = btf__fd(obj->btf);
>> +       btf_fd = bpf_object__btf_fd(obj);
>
>oh, my bad, sorry about that. But I'd still like to stick to using
>btf__fd(), so maybe let's fix forward by dropping btf_fd variable here
>and doing what bpf_object__create_map() does:
>
>if (obj->btf && btf__fd(obj->btf) >= 0 && kernel_supports(...)) {
>    load_attr.prog_btf_fd = btf__fd(obj->btf);
>    ...
>}
>
>?

I half-expected that :). I don't mind at all, I'll send an updated version tomorrow. Thanks!
diff mbox series

Patch

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index efab29b8935b..0f9a4d232468 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -7343,7 +7343,7 @@  static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog
 	load_attr.prog_ifindex = prog->prog_ifindex;
 
 	/* specify func_info/line_info only if kernel supports them */
-	btf_fd = btf__fd(obj->btf);
+	btf_fd = bpf_object__btf_fd(obj);
 	if (btf_fd >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
 		load_attr.prog_btf_fd = btf_fd;
 		load_attr.func_info = prog->func_info;