linux-kernel - Re: [PATCH v1 1/3] Revert "cgroup: enable cgroup_get_from

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Date:   Mon, 10 Oct 2022 14:03:08 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Yonghong Song <yhs@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, "Christian A . Ehrhardt" <lk@...e.de>
Subject: Re: [PATCH v1 1/3] Revert "cgroup: enable cgroup_get_from_file() on
 cgroup1"

Hello,

Already queued the following to cgroup/for-6.1-fixes. Will send it out soon.

Thanks.

----- 8< -----
>From 03db7716159477b595e9af01be8003b7e994cc79 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@...nel.org>
Date: Mon, 10 Oct 2022 11:08:17 -1000
Subject: [PATCH] Revert "cgroup: enable cgroup_get_from_file() on cgroup1"

This reverts commit f3a2aebdd6fb90e444d595e46de64e822af419da.

The commit enabled looking up v1 cgroups via cgroup_get_from_file().
However, there are multiple users, including CLONE_INTO_CGROUP, which have
been assuming that it would only look up v2 cgroups. Returning v1 cgroups
breaks them.

Let's revert the commit and retry later with a separate lookup interface
which allows both v1 and v2.

Signed-off-by: Tejun Heo <tj@...nel.org>
Link: http://lkml.kernel.org/r/000000000000385cbf05ea3f1862@google.com
Cc: Yosry Ahmed <yosryahmed@...gle.com>
---
 kernel/cgroup/cgroup.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index ecf409e3c3a7..6d8a5a40c24d 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6234,6 +6234,11 @@ static struct cgroup *cgroup_get_from_file(struct file *f)
 		return ERR_CAST(css);
 
 	cgrp = css->cgroup;
+	if (!cgroup_on_dfl(cgrp)) {
+		cgroup_put(cgrp);
+		return ERR_PTR(-EBADF);
+	}
+
 	return cgrp;
 }
 
-- 
2.37.3