netdev - Re: [PATCH bpf-next 11/15] bpf: Add bpf_sys

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Message-ID: <YHpZGeOcermVlQVF@zeniv-ca.linux.org.uk>
Date:   Sat, 17 Apr 2021 03:42:17 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     davem@...emloft.net, daniel@...earbox.net, andrii@...nel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH bpf-next 11/15] bpf: Add bpf_sys_close() helper.

On Fri, Apr 16, 2021 at 08:32:20PM -0700, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@...nel.org>
> 
> Add bpf_sys_close() helper to be used by the syscall/loader program to close
> intermediate FDs and other cleanup.

Conditional NAK.  In a lot of contexts close_fd() is very much unsafe.
In particular, anything that might call it between fdget() and fdput()
is Right Fucking Out(tm).

In which contexts can that thing be executed?