From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5E254C46CD2 for ; Sat, 27 Jan 2024 04:54:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B743B6B0074; Fri, 26 Jan 2024 23:54:10 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B237D6B0078; Fri, 26 Jan 2024 23:54:10 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9EB2B6B007B; Fri, 26 Jan 2024 23:54:10 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 8C5C46B0074 for ; Fri, 26 Jan 2024 23:54:10 -0500 (EST) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 3129D1606B1 for ; Sat, 27 Jan 2024 04:54:10 +0000 (UTC) X-FDA: 81723874260.02.8DE0071 Received: from smtp-relay-canonical-1.canonical.com (smtp-relay-canonical-1.canonical.com [185.125.188.121]) by imf29.hostedemail.com (Postfix) with ESMTP id 02A6B120006 for ; Sat, 27 Jan 2024 04:54:07 +0000 (UTC) Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=canonical.com header.s=20210705 header.b=YWoJPUSi; dmarc=pass (policy=none) header.from=canonical.com; spf=pass (imf29.hostedemail.com: domain of john.johansen@canonical.com designates 185.125.188.121 as permitted sender) smtp.mailfrom=john.johansen@canonical.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1706331248; a=rsa-sha256; cv=none; b=EVPeOEcvtFPkOiZ9gWStl2sBW3H8YiMVU4NwEtQGBLZMZ4z+y4bWXSmTISGwP8PLInYLOo 8JIVLZizNgLlTTGmgBLVg3jbBLxhbcmrmFOdtKDYo/g0/XX5IfDCfVY3tp1sQDDYtq8kdT 45qG7Uze96kmph5Sj10tF97ulWv8faY= ARC-Authentication-Results: i=1; imf29.hostedemail.com; dkim=pass header.d=canonical.com header.s=20210705 header.b=YWoJPUSi; dmarc=pass (policy=none) header.from=canonical.com; spf=pass (imf29.hostedemail.com: domain of john.johansen@canonical.com designates 185.125.188.121 as permitted sender) smtp.mailfrom=john.johansen@canonical.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1706331248; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=5WPgKmWsxsze4yg1WX8Fw9bzUlXpaO5ltG37GOwu2Sw=; b=sV+hCJt8fZoy5aCMDb94poTg3aNWfjs3lfECz0x+CXugL5Dtv7c7O8A45TH8nvhtGI/drR AGy3YNiiKMSPLo0hiAzMQ7FdqX3ohEfaJKfGngZ3OAX9XBQsTonUuiR+ud1VsAgwfbOYAD Yx+QCW5bZ1cOsyrSPZ4uipasVVycAK8= Received: from [192.168.192.85] (unknown [50.39.103.33]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by smtp-relay-canonical-1.canonical.com (Postfix) with ESMTPSA id D151B3FE86; Sat, 27 Jan 2024 04:54:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=canonical.com; s=20210705; t=1706331245; bh=5WPgKmWsxsze4yg1WX8Fw9bzUlXpaO5ltG37GOwu2Sw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YWoJPUSiaYGiIC25TTkda9fHpLf0/hC7qRCRUwrLKpauF+d5RavH9uMlpmqVY6+fC msVNW745+H9p13uwfGnAuiVpSlUg9MPO8sWMbOdpSaXwkPT3Qze7vX3pPhECJRH3RL pU1qHhDAuvfrEZtNQvhnoO5+OPebxAUrivRyV2G0rLgXqRfZX/xUyLs90AJoV45m87 Tm+SsU80twLuGJOk0B59b/16eHHvqHdhzd6ef7FKMOpZZqHbLS9cnVQeWZ2+MWQU2z YKPQDgJfnc1WFakMzYfSoQrzTYuz7wwva++KKpQycG8KtThacsTHe7+nd/QhABnpRa C48v1ZWXR0Rrw== Message-ID: <4bb5dd09-9e09-477b-9ea8-d7b9d2fb4760@canonical.com> Date: Fri, 26 Jan 2024 20:53:58 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] exec: Check __FMODE_EXEC instead of in_execve for LSMs Content-Language: en-US To: =?UTF-8?Q?Micka=C3=ABl_Sala=C3=BCn?= , Kees Cook Cc: Linus Torvalds , Jann Horn , Josh Triplett , Kevin Locke , Paul Moore , James Morris , "Serge E. Hallyn" , Kentaro Takeda , Tetsuo Handa , Alexander Viro , Christian Brauner , Jan Kara , Eric Biederman , Andrew Morton , Sebastian Andrzej Siewior , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org References: <20240124192228.work.788-kees@kernel.org> <202401241206.031E2C75B@keescook> <202401241310.0A158998@keescook> <20240125.bais0ieKahz7@digikod.net> From: John Johansen Autocrypt: addr=john.johansen@canonical.com; keydata= xsFNBE5mrPoBEADAk19PsgVgBKkImmR2isPQ6o7KJhTTKjJdwVbkWSnNn+o6Up5knKP1f49E BQlceWg1yp/NwbR8ad+eSEO/uma/K+PqWvBptKC9SWD97FG4uB4/caomLEU97sLQMtnvGWdx rxVRGM4anzWYMgzz5TZmIiVTZ43Ou5VpaS1Vz1ZSxP3h/xKNZr/TcW5WQai8u3PWVnbkjhSZ PHv1BghN69qxEPomrJBm1gmtx3ZiVmFXluwTmTgJOkpFol7nbJ0ilnYHrA7SX3CtR1upeUpM a/WIanVO96WdTjHHIa43fbhmQube4txS3FcQLOJVqQsx6lE9B7qAppm9hQ10qPWwdfPy/+0W 6AWtNu5ASiGVCInWzl2HBqYd/Zll93zUq+NIoCn8sDAM9iH+wtaGDcJywIGIn+edKNtK72AM gChTg/j1ZoWH6ZeWPjuUfubVzZto1FMoGJ/SF4MmdQG1iQNtf4sFZbEgXuy9cGi2bomF0zvy BJSANpxlKNBDYKzN6Kz09HUAkjlFMNgomL/cjqgABtAx59L+dVIZfaF281pIcUZzwvh5+JoG eOW5uBSMbE7L38nszooykIJ5XrAchkJxNfz7k+FnQeKEkNzEd2LWc3QF4BQZYRT6PHHga3Rg ykW5+1wTMqJILdmtaPbXrF3FvnV0LRPcv4xKx7B3fGm7ygdoowARAQABzStKb2huIEpvaGFu c2VuIDxqb2huLmpvaGFuc2VuQGNhbm9uaWNhbC5jb20+wsF3BBMBCgAhBQJOjRdaAhsDBQsJ CAcDBRUKCQgLBRYCAwEAAh4BAheAAAoJEAUvNnAY1cPYi0wP/2PJtzzt0zi4AeTrI0w3Rj8E Waa1NZWw4GGo6ehviLfwGsM7YLWFAI8JB7gsuzX/im16i9C3wHYXKs9WPCDuNlMc0rvivqUI JXHHfK7UHtT0+jhVORyyVVvX+qZa7HxdZw3jK+ROqUv4bGnImf31ll99clzo6HpOY59soa8y 66/lqtIgDckcUt/1ou9m0DWKwlSvulL1qmD25NQZSnvB9XRZPpPd4bea1RTa6nklXjznQvTm MdLq5aJ79j7J8k5uLKvE3/pmpbkaieEsGr+azNxXm8FPcENV7dG8Xpd0z06E+fX5jzXHnj69 DXXc3yIvAXsYZrXhnIhUA1kPQjQeNG9raT9GohFPMrK48fmmSVwodU8QUyY7MxP4U6jE2O9L 7v7AbYowNgSYc+vU8kFlJl4fMrX219qU8ymkXGL6zJgtqA3SYHskdDBjtytS44OHJyrrRhXP W1oTKC7di/bb8jUQIYe8ocbrBz3SjjcL96UcQJecSHu0qmUNykgL44KYzEoeFHjr5dxm+DDg OBvtxrzd5BHcIbz0u9ClbYssoQQEOPuFmGQtuSQ9FmbfDwljjhrDxW2DFZ2dIQwIvEsg42Hq 5nv/8NhW1whowliR5tpm0Z0KnQiBRlvbj9V29kJhs7rYeT/dWjWdfAdQSzfoP+/VtPRFkWLr 0uCwJw5zHiBgzsFNBE5mrPoBEACirDqSQGFbIzV++BqYBWN5nqcoR+dFZuQL3gvUSwku6ndZ vZfQAE04dKRtIPikC4La0oX8QYG3kI/tB1UpEZxDMB3pvZzUh3L1EvDrDiCL6ef93U+bWSRi GRKLnNZoiDSblFBST4SXzOR/m1wT/U3Rnk4rYmGPAW7ltfRrSXhwUZZVARyJUwMpG3EyMS2T dLEVqWbpl1DamnbzbZyWerjNn2Za7V3bBrGLP5vkhrjB4NhrufjVRFwERRskCCeJwmQm0JPD IjEhbYqdXI6uO+RDMgG9o/QV0/a+9mg8x2UIjM6UiQ8uDETQha55Nd4EmE2zTWlvxsuqZMgy W7gu8EQsD+96JqOPmzzLnjYf9oex8F/gxBSEfE78FlXuHTopJR8hpjs6ACAq4Y0HdSJohRLn 5r2CcQ5AsPEpHL9rtDW/1L42/H7uPyIfeORAmHFPpkGFkZHHSCQfdP4XSc0Obk1olSxqzCAm uoVmRQZ3YyubWqcrBeIC3xIhwQ12rfdHQoopELzReDCPwmffS9ctIb407UYfRQxwDEzDL+m+ TotTkkaNlHvcnlQtWEfgwtsOCAPeY9qIbz5+i1OslQ+qqGD2HJQQ+lgbuyq3vhefv34IRlyM sfPKXq8AUTZbSTGUu1C1RlQc7fpp8W/yoak7dmo++MFS5q1cXq29RALB/cfpcwARAQABwsFf BBgBCgAJBQJOZqz6AhsMAAoJEAUvNnAY1cPYP9cP/R10z/hqLVv5OXWPOcpqNfeQb4x4Rh4j h/jS9yjes4uudEYU5xvLJ9UXr0wp6mJ7g7CgjWNxNTQAN5ydtacM0emvRJzPEEyujduesuGy a+O6dNgi+ywFm0HhpUmO4sgs9SWeEWprt9tWrRlCNuJX+u3aMEQ12b2lslnoaOelghwBs8IJ r998vj9JBFJgdeiEaKJLjLmMFOYrmW197As7DTZ+R7Ef4gkWusYFcNKDqfZKDGef740Xfh9d yb2mJrDeYqwgKb7SF02Hhp8ZnohZXw8ba16ihUOnh1iKH77Ff9dLzMEJzU73DifOU/aArOWp JZuGJamJ9EkEVrha0B4lN1dh3fuP8EjhFZaGfLDtoA80aPffK0Yc1R/pGjb+O2Pi0XXL9AVe qMkb/AaOl21F9u1SOosciy98800mr/3nynvid0AKJ2VZIfOP46nboqlsWebA07SmyJSyeG8c XA87+8BuXdGxHn7RGj6G+zZwSZC6/2v9sOUJ+nOna3dwr6uHFSqKw7HwNl/PUGeRqgJEVu++ +T7sv9+iY+e0Y+SolyJgTxMYeRnDWE6S77g6gzYYHmcQOWP7ZMX+MtD4SKlf0+Q8li/F9GUL p0rw8op9f0p1+YAhyAd+dXWNKf7zIfZ2ME+0qKpbQnr1oizLHuJX/Telo8KMmHter28DPJ03 lT9Q Organization: Canonical In-Reply-To: <20240125.bais0ieKahz7@digikod.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 02A6B120006 X-Stat-Signature: ob93mnfu5pa3ubs41gj5crikcujg9fuc X-HE-Tag: 1706331247-482153 X-HE-Meta: U2FsdGVkX1+QqwUyxpHAvP+/OoRTJZLTp5E+rwY3ryMIdEIcY0X1EW7SGvvUPUl946TUOo/5zPhCB45lQaWgARpS8DABIvy7peuwxLm3F/Pliks8aMPCceMp3yrRdLYCElvmeJw/aCGauGTIvY5HxXYe27Sx3gVBcARVvCo+A8M/aoAwu9JrQALpGZCWeTjrigFz7oqqMdUQNBZoNGX+K98ABue7VQYCZRuEGbAdEKeQ4EIJ7NkWfzOmxh38j0WqZzrucGCF1RiXHkZTVwwde/aKSpcAoxwAIkP2r0s9tWg8mV5INOLeAApeZCims9kYiSqjjGJde+/Ju9d45EmJpiWO72ZKNq4v3WgKqaiDPxZfY/AaQIFO5O146lSXgOGRfBHl9Wld/QjP5m9i5DCejBP2I+B+bXe+8UmZeCY0tDmJuJXYZrKU1JhHCV2hwycNC4qCA7PFxjtvHmvYfjW8ynC8Oa5/TLttKdADOFzIZErljujjTgskEQArCL0VYCp/Hg+kHU4y50uQuzNuQSdX7VDBjpQkLWdiYO1J2r0zEA3RAcp//25TzdLIHXS8/nbwn2fnCooKcv34aBg4hLYB/lxQMAHEx3aJTHq6GuNTCDN6Rcyck3Y6gzs95Pf8hqEZ57cLNmuxg3EvUa9U4yQ/ILyDC/FT4nGeXZhYdxXURQ4lEdA7dLmlrWuH1fgSQ/wKnTWzEmRrAXBusGtulDaXU1ghqjWc7ZwUF0hhLu/tc3+7Hx/RtmlrBAJsgIY5wekfr06ilKe7fR1zB8QcDfvPBq2TAvX/gvnFgn4fKTWYNchr+hmtaWIUkmrLDBRzKeJ09f68QPq5ehOI7ItFCd7WczxEMInJArhHyt4qzuxwuJ+2nZdNwRvEk4reNvfeJRgQ4rVzAjwlWHlO7X+1hznxhAScqNpjWDolpsd3u7EKBhr4FPWWxW3Vvyv62K1QjQ6uw2lAHMjm0HFoM3DbxnH oGp1cfTK VBBa37+vV6w/AYKNpYvS4KesCBcfFrLVUUWQdzRctCTLYv66jRBFQ+C8dZb4LkZAOibxoORYENzHnwIsHwVUDF+wv6a8n0numCssj2eCFjkL6Ak5gMzH1XcZR6wQ2ZHczYBr5gscElJFw/adlPgDN5yrqQQNBPVe/NS9ODjB0pL3EfpoJE5351gHo0jVpHjr9C92yIPPinDauMnqZV5jeLNY+8NoSLvJwuDtX5cCU+A3cODFRs1qhTOzYE9nNAgmotiH60N01OYYhYqRxPacd6lAF+xkvPGE0aWygX19WlYNfjXKEJATgWIFxa7OrCydwtqxxciPdVmpMpeEOy6HFmUdrHM9XU91uBzXT2DLbMPo09HTMcnolJtKKoEzgqgvVYmMaXD+8wz+ucHgujlm3xktQQ1jk7eUNfXbf0qeepzJF7WSEISzAQpDLkK6jO1O2iAZZ 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: List-Subscribe: List-Unsubscribe: On 1/25/24 08:38, Mickaël Salaün wrote: > On Wed, Jan 24, 2024 at 01:32:02PM -0800, Kees Cook wrote: >> On Wed, Jan 24, 2024 at 12:47:34PM -0800, Linus Torvalds wrote: >>> On Wed, 24 Jan 2024 at 12:15, Kees Cook wrote: >>>> >>>> Hmpf, and frustratingly Ubuntu (and Debian) still builds with >>>> CONFIG_USELIB, even though it was reported[2] to them almost 4 years ago. >> >> For completeness, Fedora hasn't had CONFIG_USELIB for a while now. >> >>> Well, we could just remove the __FMODE_EXEC from uselib. >>> >>> It's kind of wrong anyway. >> >> Yeah. >> >>> So I think just removing __FMODE_EXEC would just do the >>> RightThing(tm), and changes nothing for any sane situation. >> >> Agreed about these: >> >> - fs/fcntl.c is just doing a bitfield sanity check. >> >> - nfs_open_permission_mask(), as you say, is only checking for >> unreadable case. >> >> - fsnotify would also see uselib() as a read, but afaict, >> that's what it would see for an mmap(), so this should >> be functionally safe. >> >> This one, though, I need some more time to examine: >> >> - AppArmor, TOMOYO, and LandLock will see uselib() as an >> open-for-read, so that might still be a problem? As you >> say, it's more of a mmap() call, but that would mean >> adding something a call like security_mmap_file() into >> uselib()... > > If user space can emulate uselib() without opening a file with > __FMODE_EXEC, then there is no security reason to keep __FMODE_EXEC for > uselib(). > agreed > Removing __FMODE_EXEC from uselib() looks OK for Landlock. We use > __FMODE_EXEC to infer if a file is being open for execution i.e., by > execve(2). > apparmor the hint should be to avoid doing permission work again that we are doing in exec. That it regressed anything more than performance here is a bug, that will get fixed. > If __FMODE_EXEC is removed from uselib(), I think it should also be > backported to all stable kernels for consistency though. > hrmmm, I am not opposed to it being backported but I don't know that it should be backported. Consistency is good but its not a serious bug fix either > >> >> The issue isn't an insane "support uselib() under AppArmor" case, but >> rather "Can uselib() be used to bypass exec/mmap checks?" >> >> This totally untested patch might give appropriate coverage: >> >> diff --git a/fs/exec.c b/fs/exec.c >> index d179abb78a1c..0c9265312c8d 100644 >> --- a/fs/exec.c >> +++ b/fs/exec.c >> @@ -143,6 +143,10 @@ SYSCALL_DEFINE1(uselib, const char __user *, library) >> if (IS_ERR(file)) >> goto out; >> >> + error = security_mmap_file(file, PROT_READ | PROT_EXEC, MAP_FIXED | MAP_SHARED); >> + if (error) >> + goto exit; >> + >> /* >> * may_open() has already checked for this, so it should be >> * impossible to trip now. But we need to be extra cautious >> >>> Of course, as you say, not having CONFIG_USELIB enabled at all is the >>> _truly_ sane thing, but the only thing that used the FMODE_EXEC bit >>> were landlock and some special-case nfs stuff. >> >> Do we want to attempt deprecation again? This was suggested last time: >> https://lore.kernel.org/lkml/20200518130251.zih2s32q2rxhxg6f@wittgenstein/ >> >> -Kees >> >> -- >> Kees Cook >>