From patchwork Tue Dec 7 06:07:54 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Udipto Goswami X-Patchwork-Id: 521889 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 85DE6C433F5 for ; Tue, 7 Dec 2021 06:08:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236528AbhLGGLd (ORCPT ); Tue, 7 Dec 2021 01:11:33 -0500 Received: from alexa-out-sd-01.qualcomm.com ([199.106.114.38]:18160 "EHLO alexa-out-sd-01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230094AbhLGGLc (ORCPT ); Tue, 7 Dec 2021 01:11:32 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1638857283; x=1670393283; h=from:to:cc:subject:date:message-id:mime-version; bh=C50vMUQCSTWdZAtbvGYHo6lp8bRwpHsLvUxB4enqqvE=; b=GCPmknML1lFQCIN4dH8IAqPpSS6qF9R8zTi8QWbX3czoIjUvYcg/CgPl RNAkTxS/R4E1hX3U6ukD2KYnmC6I1lifR3gFaRq23jdNN5GynrtHH7Yf+ tX4IihYy68oDrKUrfy+7qTe0/HkC7EenpPTTptosn+3+xJozdxIqznJDr k=; Received: from unknown (HELO ironmsg03-sd.qualcomm.com) ([10.53.140.143]) by alexa-out-sd-01.qualcomm.com with ESMTP; 06 Dec 2021 22:08:03 -0800 X-QCInternal: smtphost Received: from nasanex01c.na.qualcomm.com ([10.47.97.222]) by ironmsg03-sd.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 06 Dec 2021 22:08:02 -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; Mon, 6 Dec 2021 22:08:02 -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; Mon, 6 Dec 2021 22:07:59 -0800 From: Udipto Goswami To: Felipe Balbi , Greg Kroah-Hartman , John Keeping CC: Udipto Goswami , , Pratham Pratap , Pavankumar Kondeti , Jack Pham Subject: [PATCH v6] usb: f_fs: Fix use-after-free for epfile Date: Tue, 7 Dec 2021 11:37:54 +0530 Message-ID: <1638857274-24842-1-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: nasanex01a.na.qualcomm.com (10.52.223.231) 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. Reviewed-by: John Keeping Signed-off-by: Pratham Pratap Co-developed-by: Udipto Goswami Signed-off-by: Udipto Goswami --- v6: Addressing minor code formatting. 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..6f23a66 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -1711,16 +1711,24 @@ 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 +1775,27 @@ 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); @@ -1919,12 +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)