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 85CB05372F6 for ; Tue, 13 Oct 2026 18:52:33 +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=1791917554; cv=none; b=q3M4vrhs0gI/kBh3jt54UreUyY4nuv6FNh/cYKL+1oOCVFv2ZgQipdUWNaPIprHduTDq8P82XmN6D02HgmgFUjfZIcqHDvdL5txgzpHFTiOf14OSp3WnXzmtkYvsNaM4nzwcA6TxRHB4ZE9SPWWIFKghVYE2Wz6Z6gcLeWKe2UA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791917554; c=relaxed/simple; bh=3EQdEq6vLMmw8nxcHfBLm/eOOpvL0tRiL4HnJUtsEnI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=DDlmpTo0Z6lap2EGbW0f4FIfrsXht0xwI/YX60XdHv+0JYLAStQn/HH5jK+ikMf2bEyUPK08QQ6CRSn5FFDoQ57QdRrGlLYOxiV5n7jY3M1f6/1jagz3OVcrEsTY1zEkqHhPjGF1JSe+XX4fooLb0WlGJ+sOZyJtn4738jZFW4o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=U3IlFytf; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="U3IlFytf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF5A51F00893; Tue, 13 Oct 2026 18:52:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791917553; bh=rgWgwyHXz0iObMNnF2gY8K/WZxi79SJ498ROUICOpyQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=U3IlFytfb9txtRbQJX+er/V4L2XeIdqUrN7ouy3Xg2NdTbFBZu5ADAsVMBOJBsNEo 5x9Q4YxQYhXC0NyoesO8dwuTg8LIGiAUP/r8IopNL95PTHs7kWh5zy0+RmLYerOukc QRDXbX/Cw3DCbf/AVPtqiOVIiobOJJ2qm88CQsc0srOMIZbEaOblxQMwXHIyDX8KSs 2n8RA1fFRrRX6Zlhgq3cC3NcTRVxkICPf43X+hV69+4LcYCYCZ2g4Mq1YGgxcjKs/w rr9xskP2pM60bg1QXJsU30VjiQ3ZsckvSK4bsnIqAHkn9AVgn6wnWZ0I2x6B/WHz8Z idbn0RPc3M8nw== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Sasha Levin Subject: [PATCH 6.12.y] namespace: check the mounts before reading their parents in pivot_root() Date: Tue, 13 Oct 2026 14:52:31 -0400 Message-ID: <20261013185201.667629-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026101248-uniformly-prevail-5c24@gregkh> References: <2026101248-uniformly-prevail-5c24@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 f87bdff661664..49742673e0d5c 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -4467,14 +4467,15 @@ 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