From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 10AFE35FC3D; Tue, 26 Aug 2025 14:41:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756219264; cv=none; b=B5JXBdSlvD6pxIuLzlr9dUhCUPZT5EuCCB5MMiD21wGgYtRZ9qWaPy/lx+GBiF62iVIHFGad7aPRL2+siU4RvWORatpiPpoPMT5ZHTGcDpVyc3AHu9zK3FRr3tz1sxW0AazcmKJLlIQuNNGSU+99FNuPYO+uD6RE7/oSYIKRjyo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756219264; c=relaxed/simple; bh=928HWHPPe2fhn44Tp0/jpRzDuf6vpvQo+TZD84gQmEU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=WAH69SMzwBa7VnZDCM8mStuFkwdq3lVm6VO+lcUzg3+FythU/vnAY0QZAmWHhKVHtXGg/PC+CFJeSDbPlfeca7zbJWc2g5+fYsvTm7RpVE20ydz6mDdOrTHo5kthNr0CWhnuija52gEhZmTjYIX4dsZwRtO0WPTPPsT02W0B1QI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=AhnmvD0M; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="AhnmvD0M" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6586BC4CEF1; Tue, 26 Aug 2025 14:41:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1756219263; bh=928HWHPPe2fhn44Tp0/jpRzDuf6vpvQo+TZD84gQmEU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AhnmvD0MzKk/vZCwHZmXASC9gHo86YbN01s1u1gTG00eOxg1T6oDnAqx1E81uG02z hY3N/m475sQ+jY+45m4YmZrPiGn8e1OuToZRDDPCjf2bZUWGqiJ9PGeGORcqKTZP9V 5Pn2WaoxGuCFN9uOvdxiprldUVIIYS4pjlmyIXhw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Andrei Vagin , Pavel Tikhomirov , Christian Brauner , Al Viro , Sasha Levin Subject: [PATCH 5.4 314/403] use uniform permission checks for all mount propagation changes Date: Tue, 26 Aug 2025 13:10:40 +0200 Message-ID: <20250826110915.493713213@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250826110905.607690791@linuxfoundation.org> References: <20250826110905.607690791@linuxfoundation.org> User-Agent: quilt/0.68 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-Transfer-Encoding: 8bit 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro [ Upstream commit cffd0441872e7f6b1fce5e78fb1c99187a291330 ] do_change_type() and do_set_group() are operating on different aspects of the same thing - propagation graph. The latter asks for mounts involved to be mounted in namespace(s) the caller has CAP_SYS_ADMIN for. The former is a mess - originally it didn't even check that mount *is* mounted. That got fixed, but the resulting check turns out to be too strict for userland - in effect, we check that mount is in our namespace, having already checked that we have CAP_SYS_ADMIN there. What we really need (in both cases) is * only touch mounts that are mounted. That's a must-have constraint - data corruption happens if it get violated. * don't allow to mess with a namespace unless you already have enough permissions to do so (i.e. CAP_SYS_ADMIN in its userns). That's an equivalent of what do_set_group() does; let's extract that into a helper (may_change_propagation()) and use it in both do_set_group() and do_change_type(). Fixes: 12f147ddd6de "do_change_type(): refuse to operate on unmounted/not ours mounts" Acked-by: Andrei Vagin Reviewed-by: Pavel Tikhomirov Tested-by: Pavel Tikhomirov Reviewed-by: Christian Brauner Signed-off-by: Al Viro Signed-off-by: Sasha Levin --- fs/namespace.c | 34 ++++++++++++++++++++-------------- 1 file changed, 20 insertions(+), 14 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 3c1afe60d438..c87f847c959d 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2210,6 +2210,19 @@ static int graft_tree(struct mount *mnt, struct mount *p, struct mountpoint *mp) return attach_recursive_mnt(mnt, p, mp, false); } +static int may_change_propagation(const struct mount *m) +{ + struct mnt_namespace *ns = m->mnt_ns; + + // it must be mounted in some namespace + if (IS_ERR_OR_NULL(ns)) // is_mounted() + return -EINVAL; + // and the caller must be admin in userns of that namespace + if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) + return -EPERM; + return 0; +} + /* * Sanity check the flags to change_mnt_propagation. */ @@ -2246,10 +2259,10 @@ static int do_change_type(struct path *path, int ms_flags) return -EINVAL; namespace_lock(); - if (!check_mnt(mnt)) { - err = -EINVAL; + err = may_change_propagation(mnt); + if (err) goto out_unlock; - } + if (type == MS_SHARED) { err = invent_group_ids(mnt, recurse); if (err) @@ -2634,18 +2647,11 @@ static int do_set_group(struct path *from_path, struct path *to_path) namespace_lock(); - err = -EINVAL; - /* To and From must be mounted */ - if (!is_mounted(&from->mnt)) - goto out; - if (!is_mounted(&to->mnt)) - goto out; - - err = -EPERM; - /* We should be allowed to modify mount namespaces of both mounts */ - if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN)) + err = may_change_propagation(from); + if (err) goto out; - if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN)) + err = may_change_propagation(to); + if (err) goto out; err = -EINVAL; -- 2.50.1