linux-kernel - Re: [PATCH] cgroup: Fix crash with CLONE_INTO

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Message-ID: <20221009173519.jwuissylg5haicie@wittgenstein>
Date:   Sun, 9 Oct 2022 19:35:19 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     "Christian A. Ehrhardt" <lk@...e.de>, Tejun Heo <tj@...nel.org>
Cc:     Tejun Heo <tj@...nel.org>,
        syzbot <syzbot+534ee3d24c37c411f37f@...kaller.appspotmail.com>,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com,
        Yosry Ahmed <yosryahmed@...gle.com>
Subject: Re: [PATCH] cgroup: Fix crash with CLONE_INTO_CGROUP and v1 cgroups

On Sun, Oct 09, 2022 at 03:10:36PM +0200, Christian A. Ehrhardt wrote:
> 
> Since commit f3a2aebdd6, Version 1 cgroups no longer cause an
> error when used with CLONE_INTO_CGROUP. However, the permission
> checks performed during clone assume a Version 2 cgroup.
> 
> Restore the error check for V1 cgroups in the clone() path.
> 
> Reported-by: syzbot+534ee3d24c37c411f37f@...kaller.appspotmail.com
> Link: https://lore.kernel.org/lkml/000000000000385cbf05ea3f1862@google.com/
> Fixes: f3a2aebdd6 ("cgroup: enable cgroup_get_from_file() on cgroup1")
> Signed-off-by: Christian A. Ehrhardt <lk@...e.de>
> ---

Thanks for fixing this,
Reviewed-by: Christian Brauner (Microsoft) <brauner@...nel.org>

Fwiw, @Tejun, after
f3a2aebdd6 ("cgroup: enable cgroup_get_from_file() on cgroup1")
that non-me-Christian fixes with this patch cgroup_get_from_file() looks
a bit odd. It could use sm like:

>From 0a8a5f7acbec0385ec16cd93a9cff2486fae0ecb Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@...nel.org>
Date: Sun, 9 Oct 2022 19:33:21 +0200
Subject: [PATCH] cgroup: remove unneeded local variable

Since commit f3a2aebdd6 ("cgroup: enable cgroup_get_from_file() on cgroup1")
the assigment to @cgrp has become pointless.

Signed-off-by: Christian Brauner (Microsoft) <brauner@...nel.org>
---
 kernel/cgroup/cgroup.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 8ad2c267ff47..550e7bd96b76 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6160,14 +6160,12 @@ void cgroup_fork(struct task_struct *child)
 static struct cgroup *cgroup_get_from_file(struct file *f)
 {
 	struct cgroup_subsys_state *css;
-	struct cgroup *cgrp;
 
 	css = css_tryget_online_from_dir(f->f_path.dentry, NULL);
 	if (IS_ERR(css))
 		return ERR_CAST(css);
 
-	cgrp = css->cgroup;
-	return cgrp;
+	return css->cgroup;
 }
 
 /**
-- 
2.34.1