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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FB20C433F5 for ; Fri, 19 Nov 2021 10:08:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7416961A53 for ; Fri, 19 Nov 2021 10:08:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231393AbhKSKMA (ORCPT ); Fri, 19 Nov 2021 05:12:00 -0500 Received: from alexa-out-sd-01.qualcomm.com ([199.106.114.38]:46862 "EHLO alexa-out-sd-01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229879AbhKSKL7 (ORCPT ); Fri, 19 Nov 2021 05:11:59 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1637316538; x=1668852538; h=from:to:cc:subject:date:message-id:mime-version; bh=DA1ci5gybwapyb/OMvP4TEzoqTB+eOLVMaZTNFuwrRg=; b=g/ptwFrUZ8MKyPKrwDXg99XP0fuOLKjiZtIyKPkP+7c/5gOGl304zFX0 dbAbcPbRKm1NiXWmPukZ2/0cWSQ6d9vXypqj2ZCe2oCcWJbxFcdY1L1FW uu/sVHjypgiofPHhavvyuGSFY2paMD3NA6rukabIMnNmr+AeL4v+IZcPy 4=; Received: from unknown (HELO ironmsg01-sd.qualcomm.com) ([10.53.140.141]) by alexa-out-sd-01.qualcomm.com with ESMTP; 19 Nov 2021 02:08:58 -0800 X-QCInternal: smtphost Received: from nasanex01c.na.qualcomm.com ([10.47.97.222]) by ironmsg01-sd.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Nov 2021 02:08:58 -0800 Received: from nalasex01a.na.qualcomm.com (10.47.209.196) by nasanex01c.na.qualcomm.com (10.47.97.222) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.922.19; Fri, 19 Nov 2021 02:08:57 -0800 Received: from ugoswami-linux.qualcomm.com (10.80.80.8) by nalasex01a.na.qualcomm.com (10.47.209.196) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.922.19; Fri, 19 Nov 2021 02:08:54 -0800 From: Udipto Goswami To: Felipe Balbi , Greg Kroah-Hartman CC: Udipto Goswami , , Pratham Pratap , Pavankumar Kondeti , Jack Pham Subject: [PATCH v2] usb: f_fs: Fix use-after-free for epfile Date: Fri, 19 Nov 2021 15:38:49 +0530 Message-ID: <1637316529-31605-1-git-send-email-quic_ugoswami@quicinc.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01b.na.qualcomm.com (10.46.141.250) To nalasex01a.na.qualcomm.com (10.47.209.196) Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org From: Pratham Pratap Consider a case where ffs_func_eps_disable is called from ffs_func_disable as part of composition switch and at the same time ffs_epfile_release get called from userspace. ffs_epfile_release will free up the read buffer and call ffs_data_closed which in turn destroys ffs->epfiles and mark it as NULL. While this was happening the driver has already initialized the local epfile in ffs_func_eps_disable which is now freed and waiting to acquire the spinlock. Once spinlock is acquired the driver proceeds with the stale value of epfile and tries to free the already freed read buffer causing use-after-free. Following is the illustration of the race: CPU1 CPU2 ffs_func_eps_disable epfiles (local copy) ffs_epfile_release __ffs_epfile_read_buffer_free kfree(read_buffers) kfree(epfile) (epfiles still accessible since local copy) kfree(read_buffers) Another possibility of user after free is with the read_buffers Currently, ffs_func_eps_disable & ffs_epfile_release can race, if ffs_epfile_release ran in between while ffs_func_eps_disable was executing, due to not being in any lock it can go ahead and free the read buffer, but since ffs_func_eps_disable maintains a local copy of epfiles, it will still be valid here which when tried to free again will cause a user_after_free. Following is the illustration of the case: CPU1 CPU2 ffs_func_eps_disable spin_lock_irqsave (epfile) local copy ffs_epfile_release __ffs_epfile_read_buffer_free kfree(epfile->read_buffer) __ffs_epfile_read_buffer_free kfree(epfile->read_buffer) <> Fix this races by taking epfile local copy & assigning it under spinlock and if epfile(local) is null then update it in ffs->epfiles then finally destroy it. Signed-off-by: Pratham Pratap Co-developed-by: Udipto Goswami Signed-off-by: Udipto Goswami --- v2: Fixed the tags. drivers/usb/gadget/function/f_fs.c | 44 +++++++++++++++++++++++++++++--------- 1 file changed, 34 insertions(+), 10 deletions(-) diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index 3c584da..3cdc636 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -1268,10 +1268,13 @@ static int ffs_epfile_release(struct inode *inode, struct file *file) { struct ffs_epfile *epfile = inode->i_private; + unsigned long flags; ENTER(); + spin_lock_irqsave(&epfile->ffs->eps_lock, flags); __ffs_epfile_read_buffer_free(epfile); + spin_unlock_irqrestore(&epfile->ffs->eps_lock, flags); ffs_data_closed(epfile->ffs); return 0; @@ -1711,16 +1714,23 @@ static void ffs_data_put(struct ffs_data *ffs) static void ffs_data_closed(struct ffs_data *ffs) { + struct ffs_epfile *epfile; + unsigned long flags; ENTER(); if (atomic_dec_and_test(&ffs->opened)) { if (ffs->no_disconnect) { ffs->state = FFS_DEACTIVATED; - if (ffs->epfiles) { - ffs_epfiles_destroy(ffs->epfiles, - ffs->eps_count); - ffs->epfiles = NULL; - } + spin_lock_irqsave(&ffs->eps_lock, flags); + epfile = ffs->epfiles; + ffs->epfiles = NULL; + spin_unlock_irqrestore(&ffs->eps_lock, + flags); + + if (epfile) + ffs_epfiles_destroy(epfile, + ffs->eps_count); + if (ffs->setup_state == FFS_SETUP_PENDING) __ffs_ep0_stall(ffs); } else { @@ -1767,14 +1777,25 @@ static struct ffs_data *ffs_data_new(const char *dev_name) static void ffs_data_clear(struct ffs_data *ffs) { + struct ffs_epfile *epfile; + unsigned long flags; ENTER(); ffs_closed(ffs); BUG_ON(ffs->gadget); - if (ffs->epfiles) - ffs_epfiles_destroy(ffs->epfiles, ffs->eps_count); + spin_lock_irqsave(&ffs->eps_lock, flags); + epfile = ffs->epfiles; + ffs->epfiles = NULL; + spin_unlock_irqrestore(&ffs->eps_lock, flags); + /* potential race possible between ffs_func_eps_disable + * & ffs_epfile_release therefore maintaining a local + * copy of epfile will save us from use-after-free. + */ + if (epfile) + ffs_epfiles_destroy(epfile, + ffs->eps_count); if (ffs->ffs_eventfd) eventfd_ctx_put(ffs->ffs_eventfd); @@ -1919,12 +1940,15 @@ static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count) static void ffs_func_eps_disable(struct ffs_function *func) { - struct ffs_ep *ep = func->eps; - struct ffs_epfile *epfile = func->ffs->epfiles; - unsigned count = func->ffs->eps_count; + struct ffs_ep *ep; + struct ffs_epfile *epfile; + unsigned short count; unsigned long flags; spin_lock_irqsave(&func->ffs->eps_lock, flags); + count = func->ffs->eps_count; + epfile = func->ffs->epfiles; + ep = func->eps; while (count--) { /* pending requests get nuked */ if (ep->ep) -- 2.7.4