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 350244A4F04 for ; Tue, 13 Oct 2026 23:04:40 +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=1791932682; cv=none; b=naa3ifRjeyBV7KJK5e+3RuJIurzd+AImmohKUYVT8WnKmOibCzfY9PhPuv3lO0Zsj3rccuaAAERCR9bTCSEjEqoXfm1AGGDyBkm3ienFWoLILx1vuwiqQd4SyzFoymdP/zO8IAZan6z2Iqp9QbfgwVoK0m5OMvqIPyMSKJMey5k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791932682; c=relaxed/simple; bh=CvXlApr1sqSpr8FrQqLIrLk4T/FLmkGUqGoITcrtRBo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=rcL+JYFFsXqFZbP0YLOeMDwj1fpVt6f7RWTG0UUziBCruZ4zEgpIbFFYWMzn9dDbbDdMkRsc+QqmTamTxmU74kkYAHsh5A28Dc4lr6xBJe1JUHjINfy/ePWbXKIUedM+i1tiXarQjxUThnpqkc4hnsUWfC1iuf4ZWZtMT2xDYrI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=naZjI7oD; 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="naZjI7oD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 833841F000FF; Tue, 13 Oct 2026 23:04:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791932679; bh=LWaMdoQH8fF3wIGP7V43eOHnJkSv9twBYr8AnSCYPfQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=naZjI7oDKDjMOJ1iRJlrReoQnQVwtqtn0tDhGUDXDIHgPEM1z6vR/SE/tM30lXFoL uvCwRlppXAm6J2Tul3oc0/GuwZp2Y5YIc8mQk1dk4CnwX1NODJOaemoTzeSLoY5fNI yPkJMAOTss6A42SmuzTLb44tXAmNucCtoMMCprLCKZkxI8s7V5yHdNGxLMeLtkxgMJ 9N/alWCrJFM/Tfdg1QflpeGkZ7YaDKpSs9QGYT3tSaTfcX83XuUYCGRO/ckqBBtcim 0zP6NNDo8P3sWho+RbZkgsb1hizSZjUp/HaLdFkLxnD1mX6hNtgO+5ElugYO7JE8xW vASitCXIlcS/Q== From: Sasha Levin To: stable@vger.kernel.org Cc: Christian Brauner , Sasha Levin Subject: [PATCH 6.6.y] namespace: check the mounts before reading their parents in pivot_root() Date: Tue, 13 Oct 2026 19:04:38 -0400 Message-ID: <20261013230341.828552-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026101249-monogram-subscript-9e06@gregkh> References: <2026101249-monogram-subscript-9e06@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 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 in the inline pivot_root syscall ] 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 3311e4edbc734..5ba59fe4f3e42 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -4282,14 +4282,15 @@ 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