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[74.12.30.48]) by smtp.gmail.com with ESMTPSA id t20-20020a37ea14000000b006a6d7c3a82esm9106182qkj.15.2022.07.12.07.22.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 12 Jul 2022 07:22:27 -0700 (PDT) Date: Tue, 12 Jul 2022 10:22:25 -0400 From: Peter Xu To: Ondrej Mosnacek Cc: Alexander Viro , Andrew Morton , Andrea Arcangeli , David Hildenbrand , Lokesh Gidra , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@vger.kernel.org, linux-kernel@vger.kernel.org, Robert O'Callahan Subject: Re: [RFC PATCH RESEND] userfaultfd: open userfaultfds with O_RDONLY Message-ID: References: <20220708093451.472870-1-omosnace@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220708093451.472870-1-omosnace@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=aUGC4iEi; spf=none (imf21.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657635750; a=rsa-sha256; cv=none; b=6iA4snIBjwtqr+zoQ75iXpq61XNT846lMtLoAG3F9AMCpCBHWG1ePOWfv3Vo3LCtw9VXqD 9so18Nx0VJjzf2CPaS29BEYbEYBNsrgHWYK5PCpNL54gsiC7dd9Kh3fo0EZnuFH6j3fmRy IqXWpdfla+b6Bx5d5uNHebE+o/Rg7BQ= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657635750; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=JRth/JuCuClo783o03abQL28yzBSESS3ebbCWk69Wso=; b=6gZ68L8aVY7wy+QccrmtF0QXExPTksPNRufV55UXYBgakOTF4Ip7AefLriejDsfF0PLyts 2uzJ3DCcfFoTwDohIFqHYdBhiG4ddfUobdpIukzoWzt/bH2WXPdADg9EA2itiVG++38sR8 cM/5bBPisHNZHwA4IjLEl/NxIzF3Iuw= X-Rspamd-Queue-Id: 4E9FC1C0076 Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=aUGC4iEi; spf=none (imf21.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: g7bsy5ocx4z9mdpwijmgq9djduooboh3 X-HE-Tag: 1657635750-737474 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Jul 08, 2022 at 11:34:51AM +0200, Ondrej Mosnacek wrote: > Since userfaultfd doesn't implement a write operation, it is more > appropriate to open it read-only. > > When userfaultfds are opened read-write like it is now, and such fd is > passed from one process to another, SELinux will check both read and > write permissions for the target process, even though it can't actually > do any write operation on the fd later. > > Inspired by the following bug report, which has hit the SELinux scenario > described above: > https://bugzilla.redhat.com/show_bug.cgi?id=1974559 > > Reported-by: Robert O'Callahan > Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization") > Signed-off-by: Ondrej Mosnacek Acked-by: Peter Xu -- Peter Xu