Re: [PATCH bpf v2] libbpf: sanitise map names before pinning

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Wed, Dec 2, 2020 at 3:19 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> When we added sanitising of map names before loading programs to libbpf, we
> still allowed periods in the name. While the kernel will accept these for
> the map names themselves, they are not allowed in file names when pinning
> maps. This means that bpf_object__pin_maps() will fail if called on an
> object that contains internal maps (such as sections .rodata).
>
> Fix this by replacing periods with underscores when constructing map pin
> paths. This only affects the paths generated by libbpf when
> bpf_object__ping_maps() is called with a path argument. Any pin paths set
> by bpf_map__set_pin_path() are unaffected, and it will still be up to the
> caller to avoid invalid characters in those.
>
> Fixes: 113e6b7e15e2 ("libbpf: Sanitise internal map names so they are not rejected by the kernel")
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---
> v2:
>   - Move string munging to helper function
>
>  tools/lib/bpf/libbpf.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 8d05132e1945..08ff7783fb93 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7651,6 +7651,20 @@ bool bpf_map__is_pinned(const struct bpf_map *map)
>         return map->pinned;
>  }
>
> +static char *sanitize_pin_path(char *str)

don't want to be unnecessarily nitpicky, but the return of char *
suggests that this function might be allocating new string, so it's a
bit misleading. doing void function and having non-const char *str
feels most appropriate for this. Nice side-benefit: the implementation
will be even shorter :)


> +{
> +       char *s = str;
> +
> +       /* bpffs disallows periods in path names */
> +       while (*s) {
> +               if (*s == '.')
> +                       *s = '_';
> +               s++;
> +       }
> +
> +       return str;
> +}
> +
>  int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
>  {
>         struct bpf_map *map;
> @@ -7680,7 +7694,7 @@ int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
>                                 err = -ENAMETOOLONG;
>                                 goto err_unpin_maps;
>                         }
> -                       pin_path = buf;
> +                       pin_path = sanitize_pin_path(buf);
>                 } else if (!map->pin_path) {
>                         continue;
>                 }
> @@ -7724,7 +7738,7 @@ int bpf_object__unpin_maps(struct bpf_object *obj, const char *path)
>                                 return -EINVAL;
>                         else if (len >= PATH_MAX)
>                                 return -ENAMETOOLONG;
> -                       pin_path = buf;
> +                       pin_path = sanitize_pin_path(buf);
>                 } else if (!map->pin_path) {
>                         continue;
>                 }
> --
> 2.29.2
>