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=-10.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_MED,USER_AGENT_GIT,USER_IN_DEF_DKIM_WL 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 D5BCCC3279B for ; Sat, 7 Jul 2018 01:53:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 889D4223C9 for ; Sat, 7 Jul 2018 01:53:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="RwtN8Ezd" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 889D4223C9 Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932671AbeGGBxw (ORCPT ); Fri, 6 Jul 2018 21:53:52 -0400 Received: from mail-yw0-f201.google.com ([209.85.161.201]:57300 "EHLO mail-yw0-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753796AbeGGBxv (ORCPT ); Fri, 6 Jul 2018 21:53:51 -0400 Received: by mail-yw0-f201.google.com with SMTP id l136-v6so12095061ywb.23 for ; Fri, 06 Jul 2018 18:53:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:date:message-id:subject:from:to:cc; bh=TJHaaE6ZCXF89EJpvmCYqc4dXzNxRO1S5nsfMmbYorQ=; b=RwtN8Ezdbe15LIzTR6W9WSu27xKcJoSr3NrV1Pshi2o8HgilalBG9itFfbugY+SG43 3B4tai0TszdTW73SrXUOqpE9SmGSyx1Jxn41qDy+WUiDnTEAYXXHQcfGmKoLbfPMJaLH O+AOh12TpZVrlFiYeMC1llJP6YGO/0suM906B/kcbn+SfUulidN7Q5WVAE2ROn9PbYDT WqKmej+HaOf7H+ByZhAgzFbbldwc1NOYwLM3X0gbsygclBlpSPcqKYc3uRTk8XN/USjG bjH1jEuE8RnZIeM4r9rImuug7tkBwhQxk2aWPjNXnHELYovvtuWhvxXvoYqlRYr8vxaj 0xkw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:date:message-id:subject:from:to:cc; bh=TJHaaE6ZCXF89EJpvmCYqc4dXzNxRO1S5nsfMmbYorQ=; b=foncKCDAMYCKK/dFWN2kml8qS/+DkdlAO9IP3dYYKPiasZgKieDo6feLDUlT89J8aV u28iChJgMLBglQ+3vw1m+TQ9jiFoNCg8PJzHfEcbtRg6t3Zu0B6QWLCUOmEW1tCCbSVH ZnvR5cf6XQSvp+gs/0F2xw6e3ib16xFiY330e8s3fOArckZ1pdDkZ+YNznQqmRod1JDz c6oBr1A7TvlC19ezZ4mAzbkIXyJiDYmK3gA0Dk0/09SFz7DRsCwa1qd69dOpgvJS2JYR UoOA35DtubuMk6frqU+UvLZuSh1w3xv3oI/G6oHSQzbO4XNy1sEscwK3Eq9OB68cZU25 b1UQ== X-Gm-Message-State: APt69E0L4rFVyMp4VopekZPchw68yKPkces1S+2InC2uav8fZJxg9Z85 nFmm/7VVdq/UQZm0d8rHQDG2Hmufuw== X-Google-Smtp-Source: AAOMgpeLzAxLFAMHZNKOtWD1tT/uU/1hHZW5baB3/ifab4cHjkb2ezTfPHJUVZxvo2hT+thG4diS4omQqQ== MIME-Version: 1.0 X-Received: by 2002:a25:b983:: with SMTP id r3-v6mr3902537ybg.58.1530928430465; Fri, 06 Jul 2018 18:53:50 -0700 (PDT) Date: Sat, 7 Jul 2018 03:53:44 +0200 Message-Id: <20180707015344.146672-1-jannh@google.com> X-Mailer: git-send-email 2.18.0.203.gfac676dfb9-goog Subject: [PATCH] staging: speakup: fix wraparound in uaccess length check From: Jann Horn To: William Hubbs , Chris Brannon , Kirk Reiser , Samuel Thibault , Greg Kroah-Hartman , jannh@google.com Cc: linux-kernel@vger.kernel.org, speakup@linux-speakup.org, devel@driverdev.osuosl.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If softsynthx_read() is called with `count < 3`, `count - 3` wraps, causing the loop to copy as much data as available to the provided buffer. If softsynthx_read() is invoked through sys_splice(), this causes an unbounded kernel write; but even when userspace just reads from it normally, a small size could cause userspace crashes. Fixes: 425e586cf95b ("speakup: add unicode variant of /dev/softsynth") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn --- Reproducer (kernel overflows userspace stack, resulting in segfault): root@debian:/home/user# cat test.c #include int main(void) { char buf[1]; read(0, buf, 1); } root@debian:/home/user# gcc -o test test.c root@debian:/home/user# ./test < /dev/softsynth [do some stuff on the console so that it prints text] Segmentation fault root@debian:/home/user# strace ./test < /dev/softsynth execve("./test", ["./test"], [/* 21 vars */]) = 0 brk(NULL) = 0x55d5977da000 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2ca2cac000 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory) open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=103509, ...}) = 0 mmap(NULL, 103509, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f2ca2c92000 close(3) = 0 access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory) open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\3\2\0\0\0\0\0"..., 832) = 832 fstat(3, {st_mode=S_IFREG|0755, st_size=1689360, ...}) = 0 mmap(NULL, 3795360, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f2ca26ed000 mprotect(0x7f2ca2882000, 2097152, PROT_NONE) = 0 mmap(0x7f2ca2a82000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x195000) = 0x7f2ca2a82000 mmap(0x7f2ca2a88000, 14752, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f2ca2a88000 close(3) = 0 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f2ca2c90000 arch_prctl(ARCH_SET_FS, 0x7f2ca2c90700) = 0 mprotect(0x7f2ca2a82000, 16384, PROT_READ) = 0 mprotect(0x55d596384000, 4096, PROT_READ) = 0 mprotect(0x7f2ca2caf000, 4096, PROT_READ) = 0 munmap(0x7f2ca2c92000, 103509) = 0 read(0, "\30\0012s\0015p\0015v\0011x\0010b\0010o\0015f\n", 1) = 23 --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=NULL} --- +++ killed by SIGSEGV +++ Segmentation fault drivers/staging/speakup/speakup_soft.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/staging/speakup/speakup_soft.c b/drivers/staging/speakup/speakup_soft.c index a61bc41b82d7..f9b405bd052d 100644 --- a/drivers/staging/speakup/speakup_soft.c +++ b/drivers/staging/speakup/speakup_soft.c @@ -228,7 +228,7 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count, init = get_initstring(); /* Keep 3 bytes available for a 16bit UTF-8-encoded character */ - while (chars_sent <= count - 3) { + while (chars_sent < count) { if (speakup_info.flushing) { speakup_info.flushing = 0; ch = '\x18'; @@ -257,6 +257,8 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count, 0x80 | (ch & 0x3f) }; + if (chars_sent + 2 > count) + break; if (copy_to_user(cp, s, sizeof(s))) return -EFAULT; @@ -269,6 +271,8 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count, 0x80 | (ch & 0x3f) }; + if (chars_sent + 3 > count) + break; if (copy_to_user(cp, s, sizeof(s))) return -EFAULT; -- 2.18.0.203.gfac676dfb9-goog