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    Subject[patch 15/71] ALSA: fix locking in snd_pcm_open*() and snd_rawmidi_open*()
    2.6.26-stable review patch.  If anyone has any objections, please let us
    know.

    ------------------
    From: Takashi Iwai <tiwai@suse.de>

    Upstream-commit-id: 399ccdc1cd4e92e541d4dacbbf18c52bd693418b

    The PCM and rawmidi open callbacks have a lock against card->controls_list
    but it takes a wrong one, card->controls_rwsem, instead of a right one
    card->ctl_files_rwlock. This patch fixes them.

    This change also fixes automatically the potential deadlocks due to
    mm->mmap_sem in munmap and copy_from/to_user, reported by Sitsofe
    Wheeler:

    A: snd_ctl_elem_user_tlv(): card->controls_rwsem => mm->mmap_sem
    B: snd_pcm_open(): card->open_mutex => card->controls_rwsem
    C: munmap: mm->mmap_sem => snd_pcm_release(): card->open_mutex

    The patch breaks the chain.

    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    sound/core/pcm.c | 4 ++--
    sound/core/rawmidi.c | 4 ++--
    2 files changed, 4 insertions(+), 4 deletions(-)

    --- a/sound/core/pcm.c
    +++ b/sound/core/pcm.c
    @@ -781,7 +781,7 @@ int snd_pcm_attach_substream(struct snd_
    return -ENODEV;

    card = pcm->card;
    - down_read(&card->controls_rwsem);
    + read_lock(&card->ctl_files_rwlock);
    list_for_each_entry(kctl, &card->ctl_files, list) {
    if (kctl->pid == current->pid) {
    prefer_subdevice = kctl->prefer_pcm_subdevice;
    @@ -789,7 +789,7 @@ int snd_pcm_attach_substream(struct snd_
    break;
    }
    }
    - up_read(&card->controls_rwsem);
    + read_unlock(&card->ctl_files_rwlock);

    switch (stream) {
    case SNDRV_PCM_STREAM_PLAYBACK:
    --- a/sound/core/rawmidi.c
    +++ b/sound/core/rawmidi.c
    @@ -418,7 +418,7 @@ static int snd_rawmidi_open(struct inode
    mutex_lock(&rmidi->open_mutex);
    while (1) {
    subdevice = -1;
    - down_read(&card->controls_rwsem);
    + read_lock(&card->ctl_files_rwlock);
    list_for_each_entry(kctl, &card->ctl_files, list) {
    if (kctl->pid == current->pid) {
    subdevice = kctl->prefer_rawmidi_subdevice;
    @@ -426,7 +426,7 @@ static int snd_rawmidi_open(struct inode
    break;
    }
    }
    - up_read(&card->controls_rwsem);
    + read_unlock(&card->ctl_files_rwlock);
    err = snd_rawmidi_kernel_open(rmidi->card, rmidi->device,
    subdevice, fflags, rawmidi_file);
    if (err >= 0)
    --


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