From nobody Sat Oct 4 17:31:18 2025 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (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 944931DF27F; Thu, 14 Aug 2025 05:51:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755150708; cv=none; b=MWLel2KHHlH2vg18oxcFlt6IP2YzZcIQEhQOGolp5/wr8jpgr9lBEhJWpSPMca6tutHfFwEOAWpG/iZnwLsxzZfGmnqdCSR+MJcmeTFsfLKjZMgQ5lUTGA1fu6XRcHgwc/QPo6u5hylFVY/e3M8WmOTYM78LF2mY7F/aThtdbrk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755150708; c=relaxed/simple; bh=yIV6jsNsYQGse3vWK+MI39lw1C5htlVqCQ7nXY2Rf3M=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=eLBBzet48SWmuIR4HjrGx3z3ZaRtE9tGE3+UrHbjFlUbtLnyw96B68yW3tYGc22aq/NZwfCccDMOZULM/k1aZOnXtz3q3mYUratFhHRNqJLAaFEP2UZqIOmxHAQqMB5Jg47eyx+dDubAuiOwwG0dcSexI9J/kD/YcgwAQvAXkME= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=YCdf99ku; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="YCdf99ku" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=9EgkRLTHf3vYcKV2S9JHcON4u9ACamEgHLf479pEIGM=; b=YCdf99kusOdEqS/HI26COGuyA6 8bwU5Yhj3S0eIFtCvEwx378OpuXKqfPOHA52d8uGlBehWmFQBYqY/RF7IZ/e+tJxBaJqtdEEYYE19 NfKKWUGd1DWrca7aikE8HFwM3G5uHNfv40bnYnq0hhh/U2Gw/N/vD8VYxBsDrLiCPPMUaoeYZwyGN PoKiyEBpCVWztsca6wlRQ1oDG1okqFH9Fbx/PooLK/HZ/nr2H1HOH7mokzh8YyEzglACiOXjtl+tX fs3CnSlBLwVcAXQW8L5F6OwzZavWgtJ0Pw6i5aZNLgfeDuVdhFE04Ntv+FNsfWL/nvFQJbwo0x0B/ QPKMoY+Q==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1umQsI-0000000HNPw-3KTL; Thu, 14 Aug 2025 05:51:42 +0000 Date: Thu, 14 Aug 2025 06:51:42 +0100 From: Al Viro To: linux-fsdevel@vger.kernel.org Cc: Tycho Andersen , Andrei Vagin , Andrei Vagin , Christian Brauner , Pavel Tikhomirov , LKML , criu@lists.linux.dev, Linux API , stable Subject: [PATCH][RFC][CFT] use uniform permission checks for all mount propagation changes Message-ID: <20250814055142.GN222315@ZenIV> References: <20250724230052.GW2580412@ZenIV> <20250726175310.GB222315@ZenIV> <20250813185601.GJ222315@ZenIV> <20250813194145.GK222315@ZenIV> <20250814044239.GM222315@ZenIV> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20250814044239.GM222315@ZenIV> Sender: Al Viro Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" [this should fix userland regression from do_change_type() fix last cycle; we have too little self-test coverage in the area, unfortunately. First approximation for selftest in the followup to this posting. Review and testing of both the patch and test would be very welcome] 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 * we only touch mounts that are mounted. Hard requirement, data corruption if that's get violated. * we 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 o= urs mounts" Signed-off-by: Al Viro --- diff --git a/fs/namespace.c b/fs/namespace.c index ddfd4457d338..a191c6519e36 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2862,6 +2862,19 @@ static int graft_tree(struct mount *mnt, struct moun= t *p, struct mountpoint *mp) return attach_recursive_mnt(mnt, p, mp); } =20 +static int may_change_propagation(const struct mount *m) +{ + struct mnt_namespace *ns =3D 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. */ @@ -2898,10 +2911,10 @@ static int do_change_type(struct path *path, int ms= _flags) return -EINVAL; =20 namespace_lock(); - if (!check_mnt(mnt)) { - err =3D -EINVAL; + err =3D may_change_propagation(mnt); + if (err) goto out_unlock; - } + if (type =3D=3D MS_SHARED) { err =3D invent_group_ids(mnt, recurse); if (err) @@ -3347,18 +3360,11 @@ static int do_set_group(struct path *from_path, str= uct path *to_path) =20 namespace_lock(); =20 - err =3D -EINVAL; - /* To and From must be mounted */ - if (!is_mounted(&from->mnt)) - goto out; - if (!is_mounted(&to->mnt)) - goto out; - - err =3D -EPERM; - /* We should be allowed to modify mount namespaces of both mounts */ - if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN)) + err =3D may_change_propagation(from); + if (err) goto out; - if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN)) + err =3D may_change_propagation(to); + if (err) goto out; =20 err =3D -EINVAL;