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    Subject[PATCH 3.13.y-ckt 073/138] ALSA: timer: Fix race at concurrent reads
    Date
    3.13.11-ckt36 -stable review patch.  If anyone has any objections, please let me know.

    ---8<------------------------------------------------------------

    From: Takashi Iwai <tiwai@suse.de>

    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 <tiwai@suse.de>
    [ kamal: backport to 3.13-stable: no tu->disconnected clause ]
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    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
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