From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Sakamoto Subject: Re: [PATCH 2/3] ALSA: control: add dimension validator for userspace element Date: Fri, 1 Jul 2016 17:30:20 +0900 Message-ID: <57762A1C.8030607@sakamocchi.jp> References: <1467346511-28051-1-git-send-email-o-takashi@sakamocchi.jp> <1467346511-28051-3-git-send-email-o-takashi@sakamocchi.jp> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp-proxy003.phy.lolipop.jp (smtp-proxy003.phy.lolipop.jp [157.7.104.44]) by alsa0.perex.cz (Postfix) with ESMTP id 7E1C52614FD for ; Fri, 1 Jul 2016 10:30:26 +0200 (CEST) In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: Takashi Iwai Cc: alsa-devel@alsa-project.org, clemens@ladisch.de, ffado-devel@lists.sf.net List-Id: alsa-devel@alsa-project.org On Jul 1 2016 16:19, Takashi Iwai wrote: > On Fri, 01 Jul 2016 06:15:10 +0200, > Takashi Sakamoto wrote: >> >> The 'dimen' field in struct snd_ctl_elem_info is used to compose all of >> members in the element as multi-dimensional matrix. The field has four >> members. Each member represents the width in each dimension level by >> element member unit. For example, if the members consist of typical >> two dimensional matrix, the dimen[0] represents the number of rows >> and dimen[1] represents the number of columns (or vise-versa). >> >> The total members in the matrix should be within the number of members in >> the element, while current implementation has no validator of this >> information. In a view of userspace applications, the information must be >> valid so that it cannot cause any bugs such as buffer-over-run. >> >> This commit adds a validator of dimension information for userspace >> applications which add new element sets. When they add the element sets >> with wrong dimension information, they receive -EINVAL. >> >> Signed-off-by: Takashi Sakamoto >> --- >> sound/core/control.c | 39 +++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 39 insertions(+) >> >> diff --git a/sound/core/control.c b/sound/core/control.c >> index a85d455..eeb080f 100644 >> --- a/sound/core/control.c >> +++ b/sound/core/control.c >> @@ -805,6 +805,43 @@ static int snd_ctl_elem_list(struct snd_card *card, >> return 0; >> } >> >> +static bool validate_element_member_dimension(struct snd_ctl_elem_info *info) >> +{ >> + unsigned int members; >> + unsigned int i = 0; >> + >> + /* The value for each level should be zero or positive. */ >> + if (info->dimen.d[0] < 0) >> + return false; >> + members = info->dimen.d[0]; >> + >> + if (members > 0) { >> + for (++i; i < ARRAY_SIZE(info->dimen.d); ++i) { >> + if (info->dimen.d[i] < 0) >> + return false; >> + if (info->dimen.d[i] == 0) >> + break; >> + >> + /* Prevention of division by zero, for safe. */ >> + if (members == 0) >> + return false; >> + /* Prevent arithmetic overflow. */ >> + if (info->dimen.d[i] > UINT_MAX / members) >> + return false; >> + >> + members *= info->dimen.d[i]; >> + } >> + } >> + >> + /* The rest of level should be zero. */ >> + for (++i; i < ARRAY_SIZE(info->dimen.d); ++i) { >> + if (info->dimen.d[i] != 0) >> + return false; >> + } >> + >> + return members <= info->count; > > Well, since the dimen is 16bit short, it's easier to check the > overflow just by comparing the value with info->count at each time > (supposing info->count being the right value). Your logic still causes arithmetic overflow. Let's assume a case that the first element of dimension info has 3 or more and the second has SHRT_MAX. It's better to avoid evaluation after calculation. > That is, something like this: > > /* If no dimension is given, it's OK */ > if (!info->dimen.d[0]) > return true; > > elements = 1; > for (i = 0; i < ARRAY_SIZE(info->dimen.d); i++) { > if (info->dimen.d[i] < 0) > return false; > if (!info->dimen.d[i]) > break; Were I you, I would insert codes to evaluate the element of dimension info; i.e. if (info->dimen.d[i] > 512) break; Here, 512 is the maximum number of members which an element can have. In this case, it's certainly an element of byte type. > elements *= info->dimen.d[i]; > /* overflow? */ > if (elements > info->count) > return false; > } > > /* The rest should be all zero */ > for (i++; i < ARRAY_SIZE(info->dimen.d); i++) > if (info->dimen.d[i]) > return false; > > return true; Regards Takashi Sakamoto