Re: [PATCH bpf-next v2] bpftool: Check map name length when map create

[Rong Tao]

On 2/12/25 05:07, Andrii Nakryiko wrote:
> On Tue, Feb 11, 2025 at 2:48 AM Quentin Monnet <qmo@xxxxxxxxxx> wrote:
> > 2025-02-11 18:38 UTC+0800 ~ Rong Tao <rtoax@xxxxxxxxxxx>
> > > From: Rong Tao <rongtao@xxxxxxxx>
> > >
> > > The size of struct bpf_map::name is BPF_OBJ_NAME_LEN (16).
> > >
> > > bpf(2) {
> > >    map_create() {
> > >      bpf_obj_name_cpy(map->name, attr->map_name, sizeof(attr->map_name));
> > >    }
> > > }
> > >
> > > When specifying a map name using bpftool map create name, no error is
> > > reported if the name length is greater than 15.
> > >
> > >      $ sudo bpftool map create /sys/fs/bpf/12345678901234567890 \
> > >          type array key 4 value 4 entries 5 name 12345678901234567890
> > >
> > > Users will think that 12345678901234567890 is legal, but this name cannot
> > > be used to index a map.
> > >
> > >      $ sudo bpftool map show name 12345678901234567890
> > >      Error: can't parse name
> > >
> > >      $ sudo bpftool map show
> > >      ...
> > >      1249: array  name 123456789012345  flags 0x0
> > >        key 4B  value 4B  max_entries 5  memlock 304B
> > >
> > >      $ sudo bpftool map show name 123456789012345
> > >      1249: array  name 123456789012345  flags 0x0
> > >        key 4B  value 4B  max_entries 5  memlock 304B
> > >
> > > The map name provided in the command line is truncated, but no error is
> > > reported. This submission checks the length of the map name.
> > >
> > > Signed-off-by: Rong Tao <rongtao@xxxxxxxx>
> >
> > Reviewed-by: Quentin Monnet <qmo@xxxxxxxxxx>
> Would it make sense to just warn but proceed with a truncated name?
> libbpf truncates the name when creating a map, but preserves the
> original name in BTF (and in memory, fetchable through
> bpf_map__name()). So from the user's perspective that map is still
> named "blah-blah-something-long", even if the kernel records just a
> prefix of that.
>
> Basically, instead of forcing users to count the first 15 characters,
> warn, but do the right thing anyways?

Yes, you're right, i'll submit v3.

Rong Tao

> > Thank you!