From patchwork Fri Nov 26 05:47:24 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Udipto Goswami X-Patchwork-Id: 12640105 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2452FC433EF for ; Fri, 26 Nov 2021 05:49:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352225AbhKZFws (ORCPT ); Fri, 26 Nov 2021 00:52:48 -0500 Received: from alexa-out-sd-01.qualcomm.com ([199.106.114.38]:46543 "EHLO alexa-out-sd-01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231645AbhKZFus (ORCPT ); Fri, 26 Nov 2021 00:50:48 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1637905656; x=1669441656; h=from:to:cc:subject:date:message-id:mime-version; bh=km6yNd9EdV6SdvLzJH+egKIdEfoAGNi44P2nv+qL6Jg=; b=yR49+pyyoMmdaQXHneTyFVckfqi81F55GRiYJgWI0kclxvAxCIIwcZ1h sTPQxJChEz6PKsvXHPQ/EtJrGlcLfGo7cyy4kRQYwFj+kiJSWUsPY9ZN9 0HJD25evwGO3ygkcol/TEknQ1s0PzJlrwpycB/vte4phTxTRHbWw1XTI9 k=; Received: from unknown (HELO ironmsg04-sd.qualcomm.com) ([10.53.140.144]) by alexa-out-sd-01.qualcomm.com with ESMTP; 25 Nov 2021 21:47:35 -0800 X-QCInternal: smtphost Received: from nasanex01c.na.qualcomm.com ([10.47.97.222]) by ironmsg04-sd.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Nov 2021 21:47:35 -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; Thu, 25 Nov 2021 21:47:35 -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; Thu, 25 Nov 2021 21:47:32 -0800 From: Udipto Goswami To: Felipe Balbi , Greg Kroah-Hartman , John Keeping CC: Udipto Goswami , , Pratham Pratap , Pavankumar Kondeti , Jack Pham Subject: [PATCH v3] usb: f_fs: Fix use-after-free for epfile Date: Fri, 26 Nov 2021 11:17:24 +0530 Message-ID: <1637905644-32618-1-git-send-email-quic_ugoswami@quicinc.com> X-Mailer: git-send-email 2.7.4 MIME-Version: 1.0 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 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_data_closed if (last file closed) ffs_data_reset ffs_data_clear ffs_epfiles_destroy spin_lock dereference epfiles Fix this races by taking epfiles local copy & assigning it under spinlock and if epfiles(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 Reported-by: kernel test robot --- v3: Fixed the commit test description, removed the snippet for protecting read_buffer since epfile protection should be enough & renamed epfile to epfiles making it consistent with the field saving. drivers/usb/gadget/function/f_fs.c | 47 +++++++++++++++++++++++++++----------- 1 file changed, 34 insertions(+), 13 deletions(-) diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index 3c584da..4edf339 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -1711,16 +1711,23 @@ static void ffs_data_put(struct ffs_data *ffs) static void ffs_data_closed(struct ffs_data *ffs) { + struct ffs_epfile *epfiles; + 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); + epfiles = ffs->epfiles; + ffs->epfiles = NULL; + spin_unlock_irqrestore(&ffs->eps_lock, + flags); + + if (epfiles) + ffs_epfiles_destroy(epfiles, + ffs->eps_count); + if (ffs->setup_state == FFS_SETUP_PENDING) __ffs_ep0_stall(ffs); } else { @@ -1767,14 +1774,25 @@ static struct ffs_data *ffs_data_new(const char *dev_name) static void ffs_data_clear(struct ffs_data *ffs) { + struct ffs_epfile *epfiles; + 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); + epfiles = 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 (epfiles) + ffs_epfiles_destroy(epfiles, + ffs->eps_count); if (ffs->ffs_eventfd) eventfd_ctx_put(ffs->ffs_eventfd); @@ -1919,21 +1937,24 @@ 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 *epfiles; + unsigned short count; unsigned long flags; spin_lock_irqsave(&func->ffs->eps_lock, flags); + count = func->ffs->eps_count; + epfiles = func->ffs->epfiles; + ep = func->eps; while (count--) { /* pending requests get nuked */ if (ep->ep) usb_ep_disable(ep->ep); ++ep; - if (epfile) { - epfile->ep = NULL; - __ffs_epfile_read_buffer_free(epfile); + if (epfiles) { + epfiles->ep = NULL; + __ffs_epfile_read_buffer_free(epfiles); ++epfile; } }