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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 6E3D6CA9EA0 for ; Fri, 18 Oct 2019 22:20:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 43A80222D1 for ; Fri, 18 Oct 2019 22:20:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571437245; bh=ne9QAjeb1S8nb93Ake9Lq8Wna3eB+iMjKjixdd5/Lj0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=NxArXqR4J5EMYeQSEsultSrG5pijc18BCYoAnCiU236RRQjc2TjDWvIii6Y6dvyWz NwNemWFUWXSWng/ckE8IUByn9zVh8AefkPAAumsrc/xF6vEsgE2Lz8g8uaqcna0LmQ 3Vmnh5SZRXUd9e6TFhCDoxz1L3teoAtWj08PtW4Q= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731730AbfJRWGf (ORCPT ); Fri, 18 Oct 2019 18:06:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:38520 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731678AbfJRWGe (ORCPT ); Fri, 18 Oct 2019 18:06:34 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0540E2245B; Fri, 18 Oct 2019 22:06:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571436394; bh=ne9QAjeb1S8nb93Ake9Lq8Wna3eB+iMjKjixdd5/Lj0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=KlQBTM4izgVXv46h8WgEUTvNCbHPb6OC2+Rn89n8wAuUel7V9433A1aFaOODwdYrU HwHpSvLW0yMUwUYDN+Gaql1Tm1pN1YQ3lzuYvNWZz5ejcPbmL8dSiBYQ9sHWC9upJY kApa2mki6kI4C94VPKGTXzr0sRVPsW/opD5H850Q= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Kees Cook , Linus Torvalds , Andrew Morton , Oleg Nesterov , Samuel Dionne-Riel , Richard Weinberger , Graham Christensen , Michal Hocko , Sasha Levin , linux-fsdevel@vger.kernel.org Subject: [PATCH AUTOSEL 4.19 045/100] exec: load_script: Do not exec truncated interpreter path Date: Fri, 18 Oct 2019 18:04:30 -0400 Message-Id: <20191018220525.9042-45-sashal@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20191018220525.9042-1-sashal@kernel.org> References: <20191018220525.9042-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@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 7cde3f46ad263..e996174cbfc02 100644 --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -14,13 +14,30 @@ #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; int retval; + /* Not ours to exec if we don't start with "#!". */ if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!')) return -ENOEXEC; @@ -33,18 +50,40 @@ 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