From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.codeaurora.org by pdx-caf-mail.web.codeaurora.org (Dovecot) with LMTP id VQdnJX08GVvKNAAAmS7hNA ; Thu, 07 Jun 2018 14:10:09 +0000 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id B89C3608B8; Thu, 7 Jun 2018 14:10:09 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on pdx-caf-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by smtp.codeaurora.org (Postfix) with ESMTP id 19549602FC; Thu, 7 Jun 2018 14:10:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 19549602FC Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933280AbeFGOJz (ORCPT + 25 others); Thu, 7 Jun 2018 10:09:55 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:39404 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932877AbeFGOJa (ORCPT ); Thu, 7 Jun 2018 10:09:30 -0400 Received: from [148.252.241.226] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1fQvbQ-0005Zx-BG; Thu, 07 Jun 2018 15:09:24 +0100 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1fQvbC-0003DT-C0; Thu, 07 Jun 2018 15:09:10 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Nicolai Stange" , "Takashi Iwai" Date: Thu, 07 Jun 2018 15:05:21 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 342/410] ALSA: seq: Fix possible UAF in snd_seq_check_queue() In-Reply-To: X-SA-Exim-Connect-IP: 148.252.241.226 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.57-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Takashi Iwai commit d0f833065221cbfcbadf19fd4102bcfa9330006a upstream. Although we've covered the races between concurrent write() and ioctl() in the previous patch series, there is still a possible UAF in the following scenario: A: user client closed B: timer irq -> snd_seq_release() -> snd_seq_timer_interrupt() -> snd_seq_free_client() -> snd_seq_check_queue() -> cell = snd_seq_prioq_cell_peek() -> snd_seq_prioq_leave() .... removing all cells -> snd_seq_pool_done() .... vfree() -> snd_seq_compare_tick_time(cell) ... Oops So the problem is that a cell is peeked and accessed without any protection until it's retrieved from the queue again via snd_seq_prioq_cell_out(). This patch tries to address it, also cleans up the code by a slight refactoring. snd_seq_prioq_cell_out() now receives an extra pointer argument. When it's non-NULL, the function checks the event timestamp with the given pointer. The caller needs to pass the right reference either to snd_seq_tick or snd_seq_realtime depending on the event timestamp type. A good news is that the above change allows us to remove the snd_seq_prioq_cell_peek(), too, thus the patch actually reduces the code size. Reviewed-by: Nicolai Stange Signed-off-by: Takashi Iwai Signed-off-by: Ben Hutchings --- sound/core/seq/seq_prioq.c | 28 ++++++++++++++-------------- sound/core/seq/seq_prioq.h | 6 ++---- sound/core/seq/seq_queue.c | 28 +++++++++------------------- 3 files changed, 25 insertions(+), 37 deletions(-) --- a/sound/core/seq/seq_prioq.c +++ b/sound/core/seq/seq_prioq.c @@ -87,7 +87,7 @@ void snd_seq_prioq_delete(struct snd_seq if (f->cells > 0) { /* drain prioQ */ while (f->cells > 0) - snd_seq_cell_free(snd_seq_prioq_cell_out(f)); + snd_seq_cell_free(snd_seq_prioq_cell_out(f, NULL)); } kfree(f); @@ -214,8 +214,18 @@ int snd_seq_prioq_cell_in(struct snd_seq return 0; } +/* return 1 if the current time >= event timestamp */ +static int event_is_ready(struct snd_seq_event *ev, void *current_time) +{ + if ((ev->flags & SNDRV_SEQ_TIME_STAMP_MASK) == SNDRV_SEQ_TIME_STAMP_TICK) + return snd_seq_compare_tick_time(current_time, &ev->time.tick); + else + return snd_seq_compare_real_time(current_time, &ev->time.time); +} + /* dequeue cell from prioq */ -struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f) +struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f, + void *current_time) { struct snd_seq_event_cell *cell; unsigned long flags; @@ -227,6 +237,8 @@ struct snd_seq_event_cell *snd_seq_prioq spin_lock_irqsave(&f->lock, flags); cell = f->head; + if (cell && current_time && !event_is_ready(&cell->event, current_time)) + cell = NULL; if (cell) { f->head = cell->next; @@ -252,18 +264,6 @@ int snd_seq_prioq_avail(struct snd_seq_p return f->cells; } - -/* peek at cell at the head of the prioq */ -struct snd_seq_event_cell *snd_seq_prioq_cell_peek(struct snd_seq_prioq * f) -{ - if (f == NULL) { - pr_debug("ALSA: seq: snd_seq_prioq_cell_in() called with NULL prioq\n"); - return NULL; - } - return f->head; -} - - static inline int prioq_match(struct snd_seq_event_cell *cell, int client, int timestamp) { --- a/sound/core/seq/seq_prioq.h +++ b/sound/core/seq/seq_prioq.h @@ -44,14 +44,12 @@ void snd_seq_prioq_delete(struct snd_seq int snd_seq_prioq_cell_in(struct snd_seq_prioq *f, struct snd_seq_event_cell *cell); /* dequeue cell from prioq */ -struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f); +struct snd_seq_event_cell *snd_seq_prioq_cell_out(struct snd_seq_prioq *f, + void *current_time); /* return number of events available in prioq */ int snd_seq_prioq_avail(struct snd_seq_prioq *f); -/* peek at cell at the head of the prioq */ -struct snd_seq_event_cell *snd_seq_prioq_cell_peek(struct snd_seq_prioq *f); - /* client left queue */ void snd_seq_prioq_leave(struct snd_seq_prioq *f, int client, int timestamp); --- a/sound/core/seq/seq_queue.c +++ b/sound/core/seq/seq_queue.c @@ -273,30 +273,20 @@ void snd_seq_check_queue(struct snd_seq_ __again: /* Process tick queue... */ - while ((cell = snd_seq_prioq_cell_peek(q->tickq)) != NULL) { - if (snd_seq_compare_tick_time(&q->timer->tick.cur_tick, - &cell->event.time.tick)) { - cell = snd_seq_prioq_cell_out(q->tickq); - if (cell) - snd_seq_dispatch_event(cell, atomic, hop); - } else { - /* event remains in the queue */ + for (;;) { + cell = snd_seq_prioq_cell_out(q->tickq, + &q->timer->tick.cur_tick); + if (!cell) break; - } + snd_seq_dispatch_event(cell, atomic, hop); } - /* Process time queue... */ - while ((cell = snd_seq_prioq_cell_peek(q->timeq)) != NULL) { - if (snd_seq_compare_real_time(&q->timer->cur_time, - &cell->event.time.time)) { - cell = snd_seq_prioq_cell_out(q->timeq); - if (cell) - snd_seq_dispatch_event(cell, atomic, hop); - } else { - /* event remains in the queue */ + for (;;) { + cell = snd_seq_prioq_cell_out(q->timeq, &q->timer->cur_time); + if (!cell) break; - } + snd_seq_dispatch_event(cell, atomic, hop); } /* free lock */