Re: [PATCH v3 bpf-next 2/4] bpf: support O_PATH FDs in BPF_OBJ_PIN and BPF_OBJ_GET commands

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On Mon, May 22, 2023 at 04:29:15PM -0700, Andrii Nakryiko wrote:
> Current UAPI of BPF_OBJ_PIN and BPF_OBJ_GET commands of bpf() syscall
> forces users to specify pinning location as a string-based absolute or
> relative (to current working directory) path. This has various
> implications related to security (e.g., symlink-based attacks), forces
> BPF FS to be exposed in the file system, which can cause races with
> other applications.
> 
> One of the feedbacks we got from folks working with containers heavily
> was that inability to use purely FD-based location specification was an
> unfortunate limitation and hindrance for BPF_OBJ_PIN and BPF_OBJ_GET
> commands. This patch closes this oversight, adding path_fd field to
> BPF_OBJ_PIN and BPF_OBJ_GET UAPI, following conventions established by
> *at() syscalls for dirfd + pathname combinations.
> 
> This now allows interesting possibilities like working with detached BPF
> FS mount (e.g., to perform multiple pinnings without running a risk of
> someone interfering with them), and generally making pinning/getting
> more secure and not prone to any races and/or security attacks.
> 
> This is demonstrated by a selftest added in subsequent patch that takes
> advantage of new mount APIs (fsopen, fsconfig, fsmount) to demonstrate
> creating detached BPF FS mount, pinning, and then getting BPF map out of
> it, all while never exposing this private instance of BPF FS to outside
> worlds.
> 
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---

Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>



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