From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794063785; b=j6nklar3Gq5RevbZyBUPKLJfIxNvUmW8NjOM07DGHuSLCiAaWyStdz8Z0m0MpKh+Tmkl DJ4f3ywdKNCylqqATUw7lR5zDh+m9JMRTpOtyASjZ3znvASqiwv3/GGknOK/64I+kywHS B7abfSeLQRKkj08QtXFm7TPQncJde3EufRSuyGvyGrQ7S+VfcBNVyGWK2RXF3FdAGAk1s LfZpP7JiZOL7IJRYi+rQhaqG/yr/4fM6jg9YVExZeei4lWF0YcIehp8WQ8cvntkW71paI vrwoApUFzaYfB5MD56MMmGlhaOfifurV/NWw9/CD7W2pKYNJIc9clx8MQes1Eleq52Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794063785; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=mWsk0CdfZ9qXhHeTi8YhrH7vSytk3dxmBEqW92Tk6Uw=; b=mAiQCE/EtjBPpN41GIUyXY7hKi/XMIBYlFKcH5bOKBY1KwL6O3ykrYDN9Y6A5KAPh4gI HX2efDWP4AK17+0CmjR/bLWLmAT4gFzVZ+IU6YDP6OtZy+FEfVRuhccdJCp+a6dlXs+K6 e/iI6JVxB8BO5z/CCfNpnhaKSLZBJ44O7aBnlwtidQ0j0m9Skh7tgjXGBC+uTYBEXeLW4 Idc3NVRE2zCrjBQGG4PjF4g0X9T+4CYqFjBXa6X0Ry1547dM59UUpXWwgoXTA8CJiJXSL /5CRKUvGUuKhMF1oUTDPHXPCfS6C+7vPeCvBeYQbaGsdcPVS3okk2WRnfpOL7Wx+79Q== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=x5TS5L6o; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3A468606EE98; Sat, 7 Nov 2026 15:03:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=x5TS5L6o Received: by smtp.kernel.org (Postfix) with ESMTPSA id A12021F0089F; Sat, 7 Nov 2026 15:03:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794063785; bh=mWsk0CdfZ9qXhHeTi8YhrH7vSytk3dxmBEqW92Tk6Uw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=x5TS5L6ouqPFZIhQJ66TWdyAeFuy50VtYXU7J1C39N7o00niMwrkAPKe6v4RzrFeh pEVlAdGAxjz59elmCXUid0A7C17HC+PwfVO/pbOeRaU7hcx2wJCzOdBHQVtEuwqTuD TYfUraJbIgv+584aTPEp/qUMy/kmLJqq5H5n4oxY= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Josef Bacik , "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 6.18 848/869] mount: refuse setns() with a shared fs_struct again Date: Sat, 7 Nov 2026 08:58:50 -0500 Message-ID: <20261107134921.565278944@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261107134852.069646174@linuxfoundation.org> References: <20261107134852.069646174@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Josef Bacik [ Upstream commit 948e604aca8af30490accf7d46d44814ffa26f80 ] mntns_install() refuses to switch the mount namespace of a task that shares its fs_struct, since root and cwd of the others would move to a namespace they are not in. It looks at nsset->fs for that. If more than the mount namespace is asked for, that is a private copy made by prepare_nsset(), which has one user by definition; commit_nsset() then writes root and cwd of the copy to the fs_struct of the task. A thread of a process with two threads, pidfd of a task in another mount namespace: setns(pidfd, CLONE_NEWNS) -EINVAL setns(pidfd, CLONE_NEWNS | CLONE_NEWUTS) 0 and after the second call the other thread, still in the old mount namespace, has lost its cwd (/tmp became /) and sees the mounts of the other namespace under /. Look at the fs_struct that is going to be changed. The second call then fails with -EINVAL like the first one. Fixes: 303cc571d107 ("nsproxy: attach to namespaces via pidfds") Cc: stable@vger.kernel.org # v5.8+ Signed-off-by: Josef Bacik Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Sasha Levin --- fs/namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/namespace.c b/fs/namespace.c index bb73b317f9e72..34e0d14c454ba 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -6376,7 +6376,7 @@ static int mntns_install(struct nsset *nsset, struct ns_common *ns) if (is_anon_ns(mnt_ns)) return -EINVAL; - if (fs->users != 1) + if (current->fs->users != 1) return -EINVAL; get_mnt_ns(mnt_ns); -- 2.53.0