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 X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA509CA9ED3 for ; Mon, 4 Nov 2019 22:27:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8BE18204EC for ; Mon, 4 Nov 2019 22:27:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572906470; bh=3fIb/XpE5v/FmqlNuybYCPwnbwJAl3gVKkv+KO2OZGw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=AMvshhADsBas1mx3KGH10w2m7VuaH7gHMR6aoOQiBgjKKEe4c7B6CIjvtVxIg0aig 1yWdbIy+TmpSM+LHuuHN2/5o036aWDlMoRJKQaUwU1z7yqwNHmgXaBlBFRyrgdAy2h dmNVNW/w2Urc9h16vb5gFfJRi+xNUU56iGmvx2rE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387526AbfKDVtw (ORCPT ); Mon, 4 Nov 2019 16:49:52 -0500 Received: from mail.kernel.org ([198.145.29.99]:41388 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387507AbfKDVts (ORCPT ); Mon, 4 Nov 2019 16:49:48 -0500 Received: from localhost (6.204-14-84.ripe.coltfrance.com [84.14.204.6]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4D03E214D8; Mon, 4 Nov 2019 21:49:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1572904187; bh=3fIb/XpE5v/FmqlNuybYCPwnbwJAl3gVKkv+KO2OZGw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Xye1jrAhiedSxORzutKvOF7Gt6dnamNJtTtdy7QPuhGGNwiTCbwz5tEvDIVOu822Q CT03B7lJt42mVDkPCfNa2ij7fSUD6JF8L85IM1gsPtaEAEBVVB7r0jxn/rDMhyNRqd witlRRVRh4b2kGtvUmiIa19h4Fn+cEauVPB0dqYM= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kees Cook , Andrew Morton , Oleg Nesterov , Samuel Dionne-Riel , Richard Weinberger , Graham Christensen , Michal Hocko , Linus Torvalds , Sasha Levin Subject: [PATCH 4.9 12/62] exec: load_script: Do not exec truncated interpreter path Date: Mon, 4 Nov 2019 22:44:34 +0100 Message-Id: <20191104211913.597157089@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191104211901.387893698@linuxfoundation.org> References: <20191104211901.387893698@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kees Cook [ Upstream commit b5372fe5dc84235dbe04998efdede3c4daa866a9 ] Commit 8099b047ecc4 ("exec: load_script: don't blindly truncate shebang string") was trying to protect against a confused exec of a truncated interpreter path. However, it was overeager and also refused to truncate arguments as well, which broke userspace, and it was reverted. This attempts the protection again, but allows arguments to remain truncated. In an effort to improve readability, helper functions and comments have been added. Co-developed-by: Linus Torvalds Signed-off-by: Kees Cook Cc: Andrew Morton Cc: Oleg Nesterov Cc: Samuel Dionne-Riel Cc: Richard Weinberger Cc: Graham Christensen Cc: Michal Hocko Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- fs/binfmt_script.c | 57 ++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 48 insertions(+), 9 deletions(-) diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c index afdf4e3cafc2a..37c2093a24d3c 100644 --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -14,14 +14,31 @@ #include #include +static inline bool spacetab(char c) { return c == ' ' || c == '\t'; } +static inline char *next_non_spacetab(char *first, const char *last) +{ + for (; first <= last; first++) + if (!spacetab(*first)) + return first; + return NULL; +} +static inline char *next_terminator(char *first, const char *last) +{ + for (; first <= last; first++) + if (spacetab(*first) || !*first) + return first; + return NULL; +} + static int load_script(struct linux_binprm *bprm) { const char *i_arg, *i_name; - char *cp; + char *cp, *buf_end; struct file *file; char interp[BINPRM_BUF_SIZE]; int retval; + /* Not ours to exec if we don't start with "#!". */ if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!')) return -ENOEXEC; @@ -34,18 +51,40 @@ static int load_script(struct linux_binprm *bprm) if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE) return -ENOENT; - /* - * This section does the #! interpretation. - * Sorta complicated, but hopefully it will work. -TYT - */ - + /* Release since we are not mapping a binary into memory. */ allow_write_access(bprm->file); fput(bprm->file); bprm->file = NULL; - bprm->buf[BINPRM_BUF_SIZE - 1] = '\0'; - if ((cp = strchr(bprm->buf, '\n')) == NULL) - cp = bprm->buf+BINPRM_BUF_SIZE-1; + /* + * This section handles parsing the #! line into separate + * interpreter path and argument strings. We must be careful + * because bprm->buf is not yet guaranteed to be NUL-terminated + * (though the buffer will have trailing NUL padding when the + * file size was smaller than the buffer size). + * + * We do not want to exec a truncated interpreter path, so either + * we find a newline (which indicates nothing is truncated), or + * we find a space/tab/NUL after the interpreter path (which + * itself may be preceded by spaces/tabs). Truncating the + * arguments is fine: the interpreter can re-read the script to + * parse them on its own. + */ + buf_end = bprm->buf + sizeof(bprm->buf) - 1; + cp = strnchr(bprm->buf, sizeof(bprm->buf), '\n'); + if (!cp) { + cp = next_non_spacetab(bprm->buf + 2, buf_end); + if (!cp) + return -ENOEXEC; /* Entire buf is spaces/tabs */ + /* + * If there is no later space/tab/NUL we must assume the + * interpreter path is truncated. + */ + if (!next_terminator(cp, buf_end)) + return -ENOEXEC; + cp = buf_end; + } + /* NUL-terminate the buffer and any trailing spaces/tabs. */ *cp = '\0'; while (cp > bprm->buf) { cp--; -- 2.20.1