On Tue, Oct 22, 2024 at 12:36 AM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote:
>
> Hi,
>
> On 10/22/2024 7:02 AM, Andrii Nakryiko wrote:
> > 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.
>
> OK.
> >>> 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?
>
> It will work after removing these CONFIG_XXX dependencies for
> BPF_LINK_TYPE() invocations.
> >
> > 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
>
> Instead of outputting a null string for a link_type which didn't invoke
> BPF_LINK_TYPE, is outputting the numerical value of link->type more
> reasonable as shown below ?
In correctly configured kernel this should never happen. So we can
have WARN() there for the NULL case and just return an error or
something.
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 2873302faf39..9a02cd914ed8 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3073,14 +3073,15 @@ static void bpf_link_show_fdinfo(struct seq_file
> *m, struct file *filp)
> const struct bpf_link *link = filp->private_data;
> const struct bpf_prog *prog = link->prog;
> char prog_tag[sizeof(prog->tag) * 2 + 1] = { };
> + enum bpf_link_type type;
>
> + if (type < ARRAY_SIZE(bpf_link_type_strs) &&
> bpf_link_type_strs[type])
> + seq_printf(m, "link_type:\t%s\n", bpf_link_type_strs[type]);
> + else
> + seq_printf(m, "link_type:\t[%d]\n", type);
> +
> + seq_printf(m, "link_id:\t%u\n", link->id);
>
> - seq_printf(m,
> - "link_type:\t%s\n"
> - "link_id:\t%u\n",
> - bpf_link_type_strs[link->type],
> - link->id);
>
> >
> > 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
>
