Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965011AbcCIXSw (ORCPT ); Wed, 9 Mar 2016 18:18:52 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:40943 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964893AbcCIXRb (ORCPT ); Wed, 9 Mar 2016 18:17:31 -0500 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Takashi Iwai , Kamal Mostafa Subject: [PATCH 3.13.y-ckt 073/138] ALSA: timer: Fix race at concurrent reads Date: Wed, 9 Mar 2016 15:13:20 -0800 Message-Id: <1457565265-15195-74-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.0 In-Reply-To: <1457565265-15195-1-git-send-email-kamal@canonical.com> References: <1457565265-15195-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.13 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2501 Lines: 94 3.13.11-ckt36 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Takashi Iwai commit 4dff5c7b7093b19c19d3a100f8a3ad87cb7cd9e7 upstream. snd_timer_user_read() has a potential race among parallel reads, as qhead and qused are updated outside the critical section due to copy_to_user() calls. Move them into the critical section, and also sanitize the relevant code a bit. Signed-off-by: Takashi Iwai [ kamal: backport to 3.13-stable: no tu->disconnected clause ] Signed-off-by: Kamal Mostafa --- sound/core/timer.c | 32 ++++++++++++++------------------ 1 file changed, 14 insertions(+), 18 deletions(-) diff --git a/sound/core/timer.c b/sound/core/timer.c index cbb127b..917c4c3 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -1891,6 +1891,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, { struct snd_timer_user *tu; long result = 0, unit; + int qhead; int err = 0; tu = file->private_data; @@ -1902,7 +1903,7 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, if ((file->f_flags & O_NONBLOCK) != 0 || result > 0) { err = -EAGAIN; - break; + goto _error; } set_current_state(TASK_INTERRUPTIBLE); @@ -1917,38 +1918,33 @@ static ssize_t snd_timer_user_read(struct file *file, char __user *buffer, if (signal_pending(current)) { err = -ERESTARTSYS; - break; + goto _error; } } + qhead = tu->qhead++; + tu->qhead %= tu->queue_size; spin_unlock_irq(&tu->qlock); - if (err < 0) - goto _error; if (tu->tread) { - if (copy_to_user(buffer, &tu->tqueue[tu->qhead++], - sizeof(struct snd_timer_tread))) { + if (copy_to_user(buffer, &tu->tqueue[qhead], + sizeof(struct snd_timer_tread))) err = -EFAULT; - goto _error; - } } else { - if (copy_to_user(buffer, &tu->queue[tu->qhead++], - sizeof(struct snd_timer_read))) { + if (copy_to_user(buffer, &tu->queue[qhead], + sizeof(struct snd_timer_read))) err = -EFAULT; - goto _error; - } } - tu->qhead %= tu->queue_size; - - result += unit; - buffer += unit; - spin_lock_irq(&tu->qlock); tu->qused--; + if (err < 0) + goto _error; + result += unit; + buffer += unit; } - spin_unlock_irq(&tu->qlock); _error: + spin_unlock_irq(&tu->qlock); return result > 0 ? result : err; } -- 2.7.0