linux-kernel - Re: [PATCH] bpf: Drop disabled LSM hooks from the sleepable set

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Message-ID: <CACYkzJ5i6DNxY3D3SqiO_LO2HBbA-EgPFdK8ZBcFNmTVWweucg@mail.gmail.com>
Date:   Sat, 23 Jan 2021 00:50:21 +0100
From:   KP Singh <kpsingh@...nel.org>
To:     Mikko Ylinen <mikko.ylinen@...ux.intel.com>
Cc:     bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        KP Singh <kpsingh@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH] bpf: Drop disabled LSM hooks from the sleepable set

On Fri, Jan 22, 2021 at 11:33 PM KP Singh <kpsingh@...nel.org> wrote:
>
> On Fri, Jan 22, 2021 at 1:32 PM Mikko Ylinen
> <mikko.ylinen@...ux.intel.com> wrote:
> >
> > Networking LSM hooks are conditionally enabled and when building the new
> > sleepable BPF LSM hooks with the networking LSM hooks disabled, the
> > following build error occurs:
> >
> > BTFIDS  vmlinux
> > FAILED unresolved symbol bpf_lsm_socket_socketpair
> >
> > To fix the error, conditionally add the networking LSM hooks to the
> > sleepable set.
> >
> > Fixes: 423f16108c9d8 ("bpf: Augment the set of sleepable LSM hooks")
> > Signed-off-by: Mikko Ylinen <mikko.ylinen@...ux.intel.com>
>
> Thanks!
>
> Acked-by: KP Singh <kpsingh@...nel.org>

Btw, I was noticing that there's another hook that is surrounded by ifdefs:

diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index 70e5e0b6d69d..f7f7754e938d 100644
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -166,7 +166,11 @@ BTF_ID(func, bpf_lsm_inode_symlink)
 BTF_ID(func, bpf_lsm_inode_unlink)
 BTF_ID(func, bpf_lsm_kernel_module_request)
 BTF_ID(func, bpf_lsm_kernfs_init_security)
+
+#ifdef CONFIG_KEYS
 BTF_ID(func, bpf_lsm_key_free)
+#endif
+
 BTF_ID(func, bpf_lsm_mmap_file)
 BTF_ID(func, bpf_lsm_netlink_send)
 BTF_ID(func, bpf_lsm_path_notify)

It would be great if you can also add this to your patch :)

I guess the cleanest solution to never let this happen would be to
incorporate this in
lsm_hook_defs.h and mark hooks as SLEEPABLE and NON_SLEEPABLE with an
extra parameter to the LSM_HOOK macro and then only generate the BTF IDs
based on this macro parameter.