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Date:   Sun, 9 Oct 2022 15:10:36 +0200
From:   "Christian A. Ehrhardt" <lk@c--e.de>
To:     Christian Brauner <brauner@kernel.org>
Cc:     Tejun Heo <tj@kernel.org>,
        syzbot <syzbot+534ee3d24c37c411f37f@syzkaller.appspotmail.com>,
        gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com,
        Yosry Ahmed <yosryahmed@google.com>
Subject: [PATCH] cgroup: Fix crash with CLONE_INTO_CGROUP and v1 cgroups
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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@syzkaller.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@c--e.de>
---
 kernel/cgroup/cgroup.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index b6e3110b3ea7..f7fc3afa88c1 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6244,6 +6244,11 @@ static int cgroup_css_set_fork(struct kernel_clone_args *kargs)
 		goto err;
 	}
 
+	if (!cgroup_on_dfl(dst_cgrp)) {
+		ret = -EBADF;
+		goto err;
+	}
+
 	if (cgroup_is_dead(dst_cgrp)) {
 		ret = -ENODEV;
 		goto err;
-- 
2.34.1