On Mon, Oct 21, 2024 at 1:18 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote:
>
> On Mon, Oct 21, 2024 at 09:39:59AM +0800, Hou Tao wrote:
> > From: Hou Tao <houtao1@xxxxxxxxxx>
> >
> > If a corresponding link type doesn't invoke BPF_LINK_TYPE(), accessing
> > bpf_link_type_strs[link->type] may result in out-of-bound access.
> >
> > To prevent such missed invocations in the future, the following static
> > assertion seems feasible:
> >
> > BUILD_BUG_ON(ARRAY_SIZE(bpf_link_type_strs) != __MAX_BPF_LINK_TYPE)
> >
> > However, this doesn't work well. The reason is that the invocation of
> > BPF_LINK_TYPE() for one link type is optional due to its CONFIG_XXX
> > dependency and the elements in bpf_link_type_strs[] will be sparse. For
> > example, if CONFIG_NET is disabled, the size of bpf_link_type_strs will
> > be BPF_LINK_TYPE_UPROBE_MULTI + 1.
> >
> > Therefore, in addition to the static assertion, remove all CONFIG_XXX
> > conditions for the invocation of BPF_LINK_TYPE(). If these CONFIG_XXX
> > conditions become necessary later, the fix may need to be revised (e.g.,
> > to check the validity of link_type in bpf_link_show_fdinfo()).
> >
> > Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
> > ---
> > include/linux/bpf_types.h | 6 ------
> > kernel/bpf/syscall.c | 2 ++
> > 2 files changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> > index fa78f49d4a9a..6b7eabe9a115 100644
> > --- a/include/linux/bpf_types.h
> > +++ b/include/linux/bpf_types.h
> > @@ -136,21 +136,15 @@ BPF_MAP_TYPE(BPF_MAP_TYPE_ARENA, arena_map_ops)
> >
> > BPF_LINK_TYPE(BPF_LINK_TYPE_RAW_TRACEPOINT, raw_tracepoint)
> > BPF_LINK_TYPE(BPF_LINK_TYPE_TRACING, tracing)
> > -#ifdef CONFIG_CGROUP_BPF
> > BPF_LINK_TYPE(BPF_LINK_TYPE_CGROUP, cgroup)
> > -#endif
> > BPF_LINK_TYPE(BPF_LINK_TYPE_ITER, iter)
> > -#ifdef CONFIG_NET
> > BPF_LINK_TYPE(BPF_LINK_TYPE_NETNS, netns)
> > BPF_LINK_TYPE(BPF_LINK_TYPE_XDP, xdp)
> > BPF_LINK_TYPE(BPF_LINK_TYPE_NETFILTER, netfilter)
> > BPF_LINK_TYPE(BPF_LINK_TYPE_TCX, tcx)
> > BPF_LINK_TYPE(BPF_LINK_TYPE_NETKIT, netkit)
> > BPF_LINK_TYPE(BPF_LINK_TYPE_SOCKMAP, sockmap)
> > -#endif
> > -#ifdef CONFIG_PERF_EVENTS
> > BPF_LINK_TYPE(BPF_LINK_TYPE_PERF_EVENT, perf)
> > -#endif
I'm not sure what's the implication here, but I'd avoid doing that.
But see below.
> > BPF_LINK_TYPE(BPF_LINK_TYPE_KPROBE_MULTI, kprobe_multi)
> > BPF_LINK_TYPE(BPF_LINK_TYPE_STRUCT_OPS, struct_ops)
> > BPF_LINK_TYPE(BPF_LINK_TYPE_UPROBE_MULTI, uprobe_multi)
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index 8cfa7183d2ef..9f335c379b05 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -3071,6 +3071,8 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
> > const struct bpf_prog *prog = link->prog;
> > char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
> >
> > + BUILD_BUG_ON(ARRAY_SIZE(bpf_link_type_strs) != __MAX_BPF_LINK_TYPE);
If this is useless, why are you adding it?
Let's instead do a NULL check inside bpf_link_show_fdinfo() to handle
sparsity. And to avoid out-of-bounds, just add
[__MAX_BPF_LINK_TYPE] = NULL,
into the definition of bpf_link_type_strs
pw-bot: cr
>
> I wonder it'd be simpler to just kill BPF_LINK_TYPE completely
> and add link names directly to bpf_link_type_strs array..
> it seems it's the only purpose of the BPF_LINK_TYPE macro
>
This seems like a bit too short-sighted approach, let's not go there just yet.
> jirka
