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=-8.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 C3C68C47258 for ; Wed, 6 May 2020 08:30:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9E51B20714 for ; Wed, 6 May 2020 08:30:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="mLUoJKiQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728681AbgEFIaU (ORCPT ); Wed, 6 May 2020 04:30:20 -0400 Received: from mail27.static.mailgun.info ([104.130.122.27]:59402 "EHLO mail27.static.mailgun.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728366AbgEFIaU (ORCPT ); Wed, 6 May 2020 04:30:20 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1588753818; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: References: Cc: To: Subject: From: Sender; bh=jzdjT5/FfPOTtWWCKqxudmO6PH7po5sH4MzlpxAcptc=; b=mLUoJKiQwJ1UcAVWjvEUgSGmHCWfHrw96LI9qtZWfMUlCWPZziU9j+Q/tf47sRCrOPNm6Hl3 jr4mFy0Cqji8j8gL/UeeCt7veyzSbVgWfzQZ6O3bREarmK66m2FTdWPKEHQYALYX4TYi4v6o I6TwDuIc3snOMqoxfm7oKn7pDzY= X-Mailgun-Sending-Ip: 104.130.122.27 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by mxa.mailgun.org with ESMTP id 5eb27599.7f608a93aca8-smtp-out-n04; Wed, 06 May 2020 08:30:17 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 58BC0C43636; Wed, 6 May 2020 08:30:17 +0000 (UTC) Received: from [192.168.0.102] (unknown [183.83.139.238]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: charante) by smtp.codeaurora.org (Postfix) with ESMTPSA id 90C41C433BA; Wed, 6 May 2020 08:30:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 90C41C433BA Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=none smtp.mailfrom=charante@codeaurora.org From: Charan Teja Kalla Subject: Re: [PATCH] dma-buf: fix use-after-free in dmabuffs_dname To: Greg KH , dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org Cc: vinmenon@codeaurora.org, sumit.semwal@linaro.org, ghackmann@google.com, fengc@google.com, linux-media@vger.kernel.org References: <1588060442-28638-1-git-send-email-charante@codeaurora.org> <20200505100806.GA4177627@kroah.com> Message-ID: <8424b2ac-3ea6-6e5b-b99c-951a569f493d@codeaurora.org> Date: Wed, 6 May 2020 14:00:10 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200505100806.GA4177627@kroah.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thank you Greg for the reply. On 5/5/2020 3:38 PM, Greg KH wrote: > On Tue, Apr 28, 2020 at 01:24:02PM +0530, Charan Teja Reddy wrote: >> The following race occurs while accessing the dmabuf object exported as >> file: >> P1 P2 >> dma_buf_release() dmabuffs_dname() >> [say lsof reading /proc//fd/] >> >> read dmabuf stored in dentry->fsdata >> Free the dmabuf object >> Start accessing the dmabuf structure >> >> In the above description, the dmabuf object freed in P1 is being >> accessed from P2 which is resulting into the use-after-free. Below is >> the dump stack reported. >> >> Call Trace: >> kasan_report+0x12/0x20 >> __asan_report_load8_noabort+0x14/0x20 >> dmabuffs_dname+0x4f4/0x560 >> tomoyo_realpath_from_path+0x165/0x660 >> tomoyo_get_realpath >> tomoyo_check_open_permission+0x2a3/0x3e0 >> tomoyo_file_open >> tomoyo_file_open+0xa9/0xd0 >> security_file_open+0x71/0x300 >> do_dentry_open+0x37a/0x1380 >> vfs_open+0xa0/0xd0 >> path_openat+0x12ee/0x3490 >> do_filp_open+0x192/0x260 >> do_sys_openat2+0x5eb/0x7e0 >> do_sys_open+0xf2/0x180 >> >> Fixes: bb2bb90 ("dma-buf: add DMA_BUF_SET_NAME ioctls") > Nit, please read the documentation for how to do a Fixes: line properly, > you need more digits: > Fixes: bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls") Will update the patch >> Reported-by:syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com >> Signed-off-by: Charan Teja Reddy > Also, any reason you didn't include the other mailing lists that > get_maintainer.pl said to? Really sorry for not sending to complete list. Added now. > And finally, no cc: stable in the s-o-b area for an issue that needs to > be backported to older kernels? Will update the patch. > >> --- >> drivers/dma-buf/dma-buf.c | 25 +++++++++++++++++++++++-- >> include/linux/dma-buf.h | 1 + >> 2 files changed, 24 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c >> index 570c923..069d8f78 100644 >> --- a/drivers/dma-buf/dma-buf.c >> +++ b/drivers/dma-buf/dma-buf.c >> @@ -25,6 +25,7 @@ >> #include >> #include >> #include >> +#include >> >> #include >> #include >> @@ -38,18 +39,34 @@ struct dma_buf_list { >> >> static struct dma_buf_list db_list; >> >> +static void dmabuf_dent_put(struct dma_buf *dmabuf) >> +{ >> + if (atomic_dec_and_test(&dmabuf->dent_count)) { >> + kfree(dmabuf->name); >> + kfree(dmabuf); >> + } > Why not just use a kref instead of an open-coded atomic value? Kref approach looks cleaner. will update the patch accordingly. >> +} >> + >> static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen) >> { >> struct dma_buf *dmabuf; >> char name[DMA_BUF_NAME_LEN]; >> size_t ret = 0; >> >> + spin_lock(&dentry->d_lock); >> dmabuf = dentry->d_fsdata; >> + if (!dmabuf || !atomic_add_unless(&dmabuf->dent_count, 1, 0)) { >> + spin_unlock(&dentry->d_lock); >> + goto out; > How can dmabuf not be valid here? > > And isn't there already a usecount for the buffer? dmabuf exported as file simply relies on that file's refcount, thus fput() releases the dmabuf. We are storing the dmabuf in the dentry->d_fsdata but there is no binding between the dentry and the dmabuf. So, flow will be like 1) P1 calls fput(dmabuf_fd) 2) P2 trying to access the file information of P1.     Eg: lsof command trying to list out the dmabuf_fd information using /proc//fd/dmabuf_fd 3) P1 calls the file->f_op->release(dmabuf_fd_file)(ends up in calling dma_buf_release()),   thus frees up the dmabuf buffer. 4) P2 access the dmabuf stored in the dentry->d_fsdata which was freed in step 3. So we need to have some refcount mechanism to avoid the use-after-free in step 4. >> + } >> + spin_unlock(&dentry->d_lock); >> dma_resv_lock(dmabuf->resv, NULL); >> if (dmabuf->name) >> ret = strlcpy(name, dmabuf->name, DMA_BUF_NAME_LEN); >> dma_resv_unlock(dmabuf->resv); >> + dmabuf_dent_put(dmabuf); >> >> +out: >> return dynamic_dname(dentry, buffer, buflen, "/%s:%s", >> dentry->d_name.name, ret > 0 ? name : ""); >> } >> @@ -80,12 +97,16 @@ static int dma_buf_fs_init_context(struct fs_context *fc) >> static int dma_buf_release(struct inode *inode, struct file *file) >> { >> struct dma_buf *dmabuf; >> + struct dentry *dentry = file->f_path.dentry; >> >> if (!is_dma_buf_file(file)) >> return -EINVAL; >> >> dmabuf = file->private_data; >> >> + spin_lock(&dentry->d_lock); >> + dentry->d_fsdata = NULL; >> + spin_unlock(&dentry->d_lock); >> BUG_ON(dmabuf->vmapping_counter); >> >> /* >> @@ -108,8 +129,7 @@ static int dma_buf_release(struct inode *inode, struct file *file) >> dma_resv_fini(dmabuf->resv); >> >> module_put(dmabuf->owner); >> - kfree(dmabuf->name); >> - kfree(dmabuf); >> + dmabuf_dent_put(dmabuf); >> return 0; >> } >> >> @@ -548,6 +568,7 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info) >> init_waitqueue_head(&dmabuf->poll); >> dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll; >> dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0; >> + atomic_set(&dmabuf->dent_count, 1); >> >> if (!resv) { >> resv = (struct dma_resv *)&dmabuf[1]; >> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h >> index 82e0a4a..a259042 100644 >> --- a/include/linux/dma-buf.h >> +++ b/include/linux/dma-buf.h >> @@ -315,6 +315,7 @@ struct dma_buf { >> struct list_head list_node; >> void *priv; >> struct dma_resv *resv; >> + atomic_t dent_count; > Isn't there other usage counters here that can support this? Adding > another one feels wrong as now we have multiple use counts, right? I couldn't see any refcount exist and couldn't find the need either, earlier. But the change bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls") requires to have one. > thanks, > > greg k-h