Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757267AbcLBEsq (ORCPT ); Thu, 1 Dec 2016 23:48:46 -0500 Received: from mail-yw0-f181.google.com ([209.85.161.181]:35249 "EHLO mail-yw0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753128AbcLBEso (ORCPT ); Thu, 1 Dec 2016 23:48:44 -0500 MIME-Version: 1.0 In-Reply-To: <5840FB45.60302@linux.intel.com> References: <1480645767-10931-1-git-send-email-baolu.lu@linux.intel.com> <5840FB45.60302@linux.intel.com> From: Baolin Wang Date: Fri, 2 Dec 2016 12:48:43 +0800 Message-ID: Subject: Re: [PATCH 1/1] usb: xhci: fix possible wild pointer To: Lu Baolu Cc: Mathias Nyman , USB , LKML , stable@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3807 Lines: 100 On 2 December 2016 at 12:40, Lu Baolu wrote: > Hi, > > On 12/02/2016 12:18 PM, Baolin Wang wrote: >> On 2 December 2016 at 10:29, Lu Baolu wrote: >>> handle_cmd_completion() frees a command structure which might >>> be still referenced by xhci->current_cmd. This might cause >>> problem when xhci->current_cmd is accessed after that. >>> >>> A real-life case could be like this. The host takes a very long >>> time to respond to a command, and the command timer is fired at >>> the same time when the command completion event arrives. The >>> command completion handler frees xhci->current_cmd before the >>> timer function can grab xhci->lock. Afterward, timer function >>> grabs the lock and go ahead with checking and setting members >>> of xhci->current_cmd. >>> >>> Cc: # v3.16+ >>> Signed-off-by: Lu Baolu >> Nice catch. I was also curious where set xhci->current_cmd to be NULL >> when current command is freed. > > Below code does: Yes, I just means you did that, but the original code did not. Sorry for confusing. > > xhci->current_cmd = list_entry(cmd->cmd_list.next, > struct xhci_command, cmd_list); > mod_timer(&xhci->cmd_timer, jiffies + XHCI_CMD_DEFAULT_TIMEOUT); > + } else if (xhci->current_cmd == cmd) { > + xhci->current_cmd = NULL; > + } else { > + xhci_warn(xhci, "WARN current_cmd doesn't match command\n"); > } > > > Best regards, > Lu Baolu > >> Tested-by: Baolin Wang >> >>> --- >>> drivers/usb/host/xhci-ring.c | 16 +++++++++++----- >>> 1 file changed, 11 insertions(+), 5 deletions(-) >>> >>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c >>> index bdf6b13..13e05f6 100644 >>> --- a/drivers/usb/host/xhci-ring.c >>> +++ b/drivers/usb/host/xhci-ring.c >>> @@ -1267,14 +1267,16 @@ void xhci_handle_command_timeout(unsigned long data) >>> bool second_timeout = false; >>> xhci = (struct xhci_hcd *) data; >>> >>> - /* mark this command to be cancelled */ >>> spin_lock_irqsave(&xhci->lock, flags); >>> - if (xhci->current_cmd) { >>> - if (xhci->current_cmd->status == COMP_CMD_ABORT) >>> - second_timeout = true; >>> - xhci->current_cmd->status = COMP_CMD_ABORT; >>> + if (!xhci->current_cmd) { >>> + spin_unlock_irqrestore(&xhci->lock, flags); >>> + return; >>> } >>> >>> + if (xhci->current_cmd->status == COMP_CMD_ABORT) >>> + second_timeout = true; >>> + xhci->current_cmd->status = COMP_CMD_ABORT; >>> + >>> /* Make sure command ring is running before aborting it */ >>> hw_ring_state = xhci_read_64(xhci, &xhci->op_regs->cmd_ring); >>> if ((xhci->cmd_ring_state & CMD_RING_STATE_RUNNING) && >>> @@ -1422,6 +1424,10 @@ static void handle_cmd_completion(struct xhci_hcd *xhci, >>> xhci->current_cmd = list_entry(cmd->cmd_list.next, >>> struct xhci_command, cmd_list); >>> mod_timer(&xhci->cmd_timer, jiffies + XHCI_CMD_DEFAULT_TIMEOUT); >>> + } else if (xhci->current_cmd == cmd) { >>> + xhci->current_cmd = NULL; >>> + } else { >>> + xhci_warn(xhci, "WARN current_cmd doesn't match command\n"); >>> } >>> >>> event_handled: >>> -- >>> 2.1.4 >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-usb" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> > -- Baolin.wang Best Regards