Re: [PATCH bpf-next 11/15] bpf: Add bpf_sys_close() helper.

On Fri, Apr 16, 2021 at 9:04 PM Al Viro [off-list ref] wrote:

On Fri, Apr 16, 2021 at 08:46:05PM -0700, Alexei Starovoitov wrote:

quoted

On Fri, Apr 16, 2021 at 8:42 PM Al Viro [off-list ref] wrote:

quoted

On Fri, Apr 16, 2021 at 08:32:20PM -0700, Alexei Starovoitov wrote:

quoted

From: Alexei Starovoitov <ast@kernel.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?

user context only.
It's not for all of bpf _obviously_.

Let me restate the question: what call chains could lead to bpf_sys_close()?

Already answered. User context only. It's all safe.