netdev - Re: [PATCH bpf v2 1/2] bpf: link: refuse non-O_RDWR flags in BPF_OBJ

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAEf4Bzaj+WgM5WEVTrZgN9oSND+_wdQoWOZYdo-sNyujZ9S0KQ@mail.gmail.com>
Date:   Sat, 27 Mar 2021 21:49:26 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Lorenz Bauer <lmb@...udflare.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        kernel-team <kernel-team@...udflare.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf v2 1/2] bpf: link: refuse non-O_RDWR flags in BPF_OBJ_GET

On Fri, Mar 26, 2021 at 9:05 AM Lorenz Bauer <lmb@...udflare.com> wrote:
>
> Invoking BPF_OBJ_GET on a pinned bpf_link checks the path access
> permissions based on file_flags, but the returned fd ignores flags.
> This means that any user can acquire a "read-write" fd for a pinned
> link with mode 0664 by invoking BPF_OBJ_GET with BPF_F_RDONLY in
> file_flags. The fd can be used to invoke BPF_LINK_DETACH, etc.
>
> Fix this by refusing non-O_RDWR flags in BPF_OBJ_GET. This works
> because OBJ_GET by default returns a read write mapping and libbpf
> doesn't expose a way to override this behaviour for programs
> and links.
>
> Fixes: 70ed506c3bbc ("bpf: Introduce pinnable bpf_link abstraction")
> Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>  kernel/bpf/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
> index 1576ff331ee4..dc56237d6960 100644
> --- a/kernel/bpf/inode.c
> +++ b/kernel/bpf/inode.c
> @@ -547,7 +547,7 @@ int bpf_obj_get_user(const char __user *pathname, int flags)
>         else if (type == BPF_TYPE_MAP)
>                 ret = bpf_map_new_fd(raw, f_flags);
>         else if (type == BPF_TYPE_LINK)
> -               ret = bpf_link_new_fd(raw);
> +               ret = (f_flags != O_RDWR) ? -EINVAL : bpf_link_new_fd(raw);
>         else
>                 return -ENOENT;
>
> --
> 2.27.0
>