linux-kernel - Re: [PATCH bpf-next 1/2] bpf: Add bpf_task_cwd_from

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: <tencent_C8CF57BAD10D440E8308A19E2C894B341507@qq.com>
Date: Fri, 30 May 2025 09:28:40 +0800
From: Rong Tao <rtoax@...mail.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, rongtao@...tc.cn,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>,
 Shuah Khan <shuah@...nel.org>, Juntong Deng <juntong.deng@...look.com>,
 Amery Hung <amery.hung@...edance.com>,
 Dave Marchevsky <davemarchevsky@...com>, Hou Tao <houtao1@...wei.com>,
 "open list:BPF [GENERAL] (Safe Dynamic Programs and Tools)"
 <bpf@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>,
 "open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/2] bpf: Add bpf_task_cwd_from_pid() kfunc


On 5/29/25 13:44, Alexei Starovoitov wrote:
> On Wed, May 28, 2025 at 8:37 PM Rong Tao <rtoax@...mail.com> wrote:
>> From: Rong Tao <rongtao@...tc.cn>
>>
>> It is a bit troublesome to get cwd based on pid in bpf program, such as
>> bpftrace example [1].
>>
>> This patch therefore adds a new bpf_task_cwd_from_pid() kfunc which
>> allows BPF programs to get cwd from a pid.
>>
>> [1] https://github.com/bpftrace/bpftrace/issues/3314
> Yes. This is cumbersome, but adding a very specific kfunc
> to the kernel is not a solution.
> This is tracing, no need for precise cwd. probe_read_kernel
> can do the job. bpftrace needs to have better C interop.
> Once that happens any kind of tracing extraction will be
> easy to write in C. Like this bpf_task_cwd_from_pid()
> can already be written as C bpf program.
Thanks for your reply, Yesterday I tried many ways to implement
the solution of getting cwd from pid/task, but all failed. The basic
idea is to rewrite the d_path() code, but in the bpf program, there
will be various memory security access problems, even if enough
  `if (!ptr)` are added, the program cannot be loaded successfully.

https://github.com/Rtoax/bcc/commit/2ba7a2389fc1183264e5195ff26561d93038886c

     bcc/tools$ sudo ./opensnoop.py -F

     ; if (dentry == vfsmnt->mnt_root || dentry == dentry->d_parent) { @ 
main.c:174
     109: (79) r2 = *(u64 *)(r7 +0)
     R7 invalid mem access 'scalar'

At the same time, bpf_d_path cannot be used because it can only be
applied to functions in btf_allowlist_d_path. Currently, it is
impossible to get cwd from pid/task in user mode. Any suggestions?

In addition, I fully tested this patch yesterday and it performed well.

Rong Tao