On Wed, Aug 21, 2024 at 10:46 AM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> On Wed, 2024-08-21 at 09:59 -0700, Andrii Nakryiko wrote:
>
> [...]
>
> > > Fixes: 74753e1462e7 ("libbpf: Replace btf__type_by_id() with btf_type_by_id().")
> > > Reported-by: Liu RuiTong <cnitlrt@xxxxxxxxx>
> > > Closes: https://lore.kernel.org/bpf/CAK55_s6do7C+DVwbwY_7nKfUz0YLDoiA1v6X3Y9+p0sWzipFSA@xxxxxxxxxxxxxx/
> > > Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> > > ---
> > > tools/lib/bpf/relo_core.c | 5 +++++
> > > 1 file changed, 5 insertions(+)
> > >
> > > diff --git a/tools/lib/bpf/relo_core.c b/tools/lib/bpf/relo_core.c
> > > index 63a4d5ad12d1..a04724831ebc 100644
> > > --- a/tools/lib/bpf/relo_core.c
> > > +++ b/tools/lib/bpf/relo_core.c
> > > @@ -1297,6 +1297,11 @@ int bpf_core_calc_relo_insn(const char *prog_name,
> > >
> > > local_id = relo->type_id;
> > > local_type = btf_type_by_id(local_btf, local_id);
> > > + if (!local_type) {
> >
> > This is a meaningless check at least for libbpf's implementation of
> > btf_type_by_id(), it never returns NULL. Commit you point to in Fixes
> > tag clearly states the differences.
>
> That is not true on kernel side.
> bpf_core_calc_relo_insn() is called from bpf_core_apply():
>
> int bpf_core_apply(struct bpf_core_ctx *ctx, const struct bpf_core_relo *relo,
> int relo_idx, void *insn)
> {
> bool need_cands = relo->kind != BPF_CORE_TYPE_ID_LOCAL;
> ...
> if (need_cands) {
> ...
> // code below would report an error if relo->type_id is bogus
> cc = bpf_core_find_cands(ctx, relo->type_id);
> if (IS_ERR(cc)) {
> bpf_log(ctx->log, "target candidate search failed for %d\n",
> relo->type_id);
> err = PTR_ERR(cc);
> goto out;
> }
> ...
> }
>
> err = bpf_core_calc_relo_insn((void *)ctx->log, relo, relo_idx, ctx->btf, &cands, specs,
> &targ_res);
> ...
> }
>
> If `need_cands` is false the bogus type_id could reach into bpf_core_calc_relo_insn().
> Which is exactly the case with repro submitted by Liu.
> There is also a simplified repro here:
> https://github.com/kernel-patches/bpf/commit/017a9dcf17e572f9b7c32aa62a81df8ef41cef17
> But I can't submit it as a test yet.
>
> >
> > So you'd need to validate local_id directly against number of types in
> > local_btf.
>
> How is this better than a null check?
>
because id check will be useful for both kernel and libbpf sides?..
> >
> > pw-bot: cr
> >
> >
> > > + pr_warn("prog '%s': relo #%d: bad type id %u\n",
> >
> > nit: this part of CO-RE-related code normally uses [%u] "syntax" to
> > point to BTF type IDs, please adjust for consistency
>
> Ok
>
