From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6955D224D6; Sat, 17 Oct 2026 16:06:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792253161; cv=none; b=chwJ+OudNlaTa4wxj3bqDHaj9lmam9unmituwaDWbNOxbqxqbIxIuDPoSTiQskJAlJSLNbMl4rH8PdhUjYMwkiVVFPCw1GPDmbGjhdTxfAFAZfRwUU9LG35jNr3d8s/0yfa8yxNErZdyzpr750PRo9v0ZiWroOz8uLzDbD3mfpo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792253161; c=relaxed/simple; bh=GIk5+Kntnjm7M+2gy4Fox+WjPfYOM6+G1fAPtjd7tHQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=VMZQJtH9TXtns8q+nkoIHYdjVHF7EINYwpNtbISBSv6ZFUEkE+HR2SPD1zEUXFaldW+oxcRvhu8XfQ3gczyIMvcfz8SDFnkNyhIua/JTBgCbfB+vgcQSpGiTywjMxi5n+iVkU5oHTfOwETHpOx70RWKP49zSyHSkRLiZZNZo7bE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=zpCNRoD/; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="zpCNRoD/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B622A1F000C4; Sat, 17 Oct 2026 16:05:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1792253160; bh=zGEYEmPjyi58Td2dJGzOYUS6BJAwJ0RMHF6M20kvL8Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=zpCNRoD/+Ig2q7m0yvmaBbD939uqbzL9oKLA+SO4CHmJmb3IW6ocEbecLLmHyEzEh XfYSrWADu7n9TMlbyq5w7kgUjr9V1OwXgQfard7psaAGTOTKNOjh3ak1+Hk+7Z7fNa SSBRFu2ZHf4W6tX4Ls7NeXLq7Z5zLeSG2vyOBt9s= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 6.12 030/869] namespace: check the mounts before reading their parents in pivot_root() Date: Sat, 17 Oct 2026 17:47:51 +0200 Message-ID: <20261017160037.787018876@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261017160036.979869304@linuxfoundation.org> References: <20261017160036.979869304@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.12-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: Replaced `return -EINVAL` with `goto out4` to preserve the syscall’s explicit cleanup path. ] 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 11e6ddce877d5..2c23537a17d19 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -4469,14 +4469,15 @@ 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