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=1793213524; b=Vo7usf4EEBR28KRmfGUYnC9PPerZrqIPJh5NAB1X3pBdX5k6AjQ2d3mninUyawP5ZH+a Ln82rgV1OJShb4/CAUogJH89K5Eeo1bhAt8GUHKePgfYQdZuPxVQ+ZUxUkJxPSqwbYtQo 8VPFlsQCRwkEj/h0RXzvIrsQSo8Q5yJljrRxIdh7rnb1PK9dmVlwSh6Y5tyRq4P/5FSCX FwT0XrtskkVjInFqNsnZ/OrJniju3+y197AFFJv55r4j5bFRoT7hzg8OkvH9MOrA9di8g ii5cCJ7w304v+n2N4tsNmeaWyZd+wJ6dG9hJyf6BYHwpwDowYMf/2woe4EsLQyAOfJw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793213524; 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=fBG/qjWhNll4+yeIwSFciKSun3ikLdS0cC4/fY/+i08=; b=Kc730oL3ncuMw/ozmua4TbdMXoCTBtHbbFXx0raJE63sOeLxprgit6sOtQYXgkVJq4wL LcogWREPg9YKod13VhsegmH4EWNbsOpD64W+qrt14cJcYeuxo0zY20QrcjXQsvYPADlVG ySfXkxeMmSqY2jchXReo6VyzJ576eZw8xDX42+gk1ebNJ0q2Zdfh/vln3J8vV8Y5rvgRM 7AEleweznxvOlC7dqS9Q1Xzr4PVclborcCTyVga/CkxIwXHsN5gPxypbkyZ6KZ0O3fQ83 6aJDNP6eCM1qsklX84y1D5iEXrrk+wD5JiilDw2dkVTJlNDHdH2oWmNjYsoXcy/BbgQ== 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=bgTwtXob; 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 CFD8B606A31A; Wed, 28 Oct 2026 18:52:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=bgTwtXob Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2FB111F01825; Wed, 28 Oct 2026 18:52:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793213523; bh=fBG/qjWhNll4+yeIwSFciKSun3ikLdS0cC4/fY/+i08=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bgTwtXobisdi3QBdV7bkST37/zpkoZs5jEEvEjWEmOI1cQV27fteH1vu5JVHL8XqK o1hZzQSzuUG7sSXM/iBWn8fvRq/De3VdSJoigefU7KamPlvEApGKAmfHQ+YavPeJqm dJEytZgieuvK2gibiG9oOkmyJq8jby17VGrnolxo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 6.1 0529/1887] namespace: check the mounts before reading their parents in pivot_root() Date: Wed, 28 Oct 2026 17:43:45 +0100 Message-ID: <20261028170511.376346105@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170459.200466217@linuxfoundation.org> References: <20261028170459.200466217@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Brauner [ Upstream commit 6b7c001eb5857fa09041f47673666060a2e5fc1c ] path_pivot_root() reads the parents of new_root and of the caller's root and checks whether they are shared before it checks that either mount is in the caller's mount namespace. Only namespace_sem is held. That's fine for a mount that is in the caller's mount namespace. But new_root can be a file descriptor to a mount that has been unmounted and that only the file descriptor keeps alive. If that mount stayed attached to its parent when it was unmounted nothing pins the parent for it. The final mntput() of the parent unhooks the children under mount_lock alone and frees the parent afterwards: pivot_root() close(fd), last ref on the parent ------------ --------------------------------- ex_parent = new_mnt->mnt_parent mntput_no_expire_slowpath() __umount_mnt(new_mnt) cleanup_mnt() call_rcu() IS_MNT_SHARED(ex_parent) BUG: KASAN: slab-use-after-free in path_pivot_root+0xf1a/0x1840 Read of size 4 at addr ffff8881047382f8 by task pivot_widen/157 path_pivot_root+0xf1a/0x1840 __x64_sys_pivot_root+0x165/0x190 The same goes for the caller's root via chroot(). Both outcomes of the check end in EINVAL so nothing but the read itself goes wrong. It's the same thing commit bb4609405752 ("statmount: read the parent of an unmounted mount under mount_lock") fixed for statmount(). Check that both mounts are in the caller's namespace before their parents are read. Every path returns EINVAL either way. Fixes: e0c9c0afd2fc ("mnt: Update detach_mounts to leave mounts connected") Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260930-work-mount-fixes-3-v1-10-be34c83956ae@kernel.org Signed-off-by: Christian Brauner (Amutable) [ sashal: adapted the check to the inline pivot_root() syscall using goto out4 instead of returning -EINVAL. ] Signed-off-by: Sasha Levin --- fs/namespace.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 2492d5286cef6..f9c3f91277244 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3973,14 +3973,15 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, new_mnt = real_mount(new.mnt); root_mnt = real_mount(root.mnt); old_mnt = real_mount(old.mnt); + /* only a mounted mount has a parent that namespace_sem pins */ + if (!check_mnt(root_mnt) || !check_mnt(new_mnt)) + goto out4; ex_parent = new_mnt->mnt_parent; root_parent = root_mnt->mnt_parent; if (IS_MNT_SHARED(old_mnt) || IS_MNT_SHARED(ex_parent) || IS_MNT_SHARED(root_parent)) goto out4; - if (!check_mnt(root_mnt) || !check_mnt(new_mnt)) - goto out4; if (new_mnt->mnt.mnt_flags & MNT_LOCKED) goto out4; error = -ENOENT; -- 2.53.0