[bug report] ALSA: rawmidi: Avoid racy info ioctl via ctl device
Dan Carpenter
dan.carpenter at oracle.com
Tue Feb 2 07:11:43 CET 2021
On Mon, Feb 01, 2021 at 02:22:10PM +0100, Takashi Iwai wrote:
> On Mon, 01 Feb 2021 13:55:16 +0100,
> Dan Carpenter wrote:
> >
> > Hello Takashi Iwai,
> >
> > The patch c1cfd9025cc3: "ALSA: rawmidi: Avoid racy info ioctl via ctl
> > device" from Dec 14, 2017, leads to the following static checker
> > warning:
> >
> > sound/core/rawmidi.c:651 snd_rawmidi_info_select()
> > warn: called with lock held. '®ister_mutex'
> >
> > sound/core/seq/seq_midi.c
> > 297 mutex_lock(®ister_mutex);
> > ^^^^^^^^^^^^^^^
> > Holding this lock.
> >
> > 298 client = synths[card->number];
> > 299 if (client == NULL) {
> > 300 newclient = 1;
> > 301 client = kzalloc(sizeof(*client), GFP_KERNEL);
> > 302 if (client == NULL) {
> > 303 mutex_unlock(®ister_mutex);
> > 304 kfree(info);
> > 305 return -ENOMEM;
> > 306 }
> > 307 client->seq_client =
> > 308 snd_seq_create_kernel_client(
> > 309 card, 0, "%s", card->shortname[0] ?
> > 310 (const char *)card->shortname : "External MIDI");
> > 311 if (client->seq_client < 0) {
> > 312 kfree(client);
> > 313 mutex_unlock(®ister_mutex);
> > 314 kfree(info);
> > 315 return -ENOMEM;
> > 316 }
> > 317 }
> > 318
> > 319 msynth = kcalloc(ports, sizeof(struct seq_midisynth), GFP_KERNEL);
> > 320 port = kmalloc(sizeof(*port), GFP_KERNEL);
> > 321 if (msynth == NULL || port == NULL)
> > 322 goto __nomem;
> > 323
> > 324 for (p = 0; p < ports; p++) {
> > 325 ms = &msynth[p];
> > 326
> > 327 if (snd_seq_midisynth_new(ms, card, device, p) < 0)
> > 328 goto __nomem;
> > 329
> > 330 /* declare port */
> > 331 memset(port, 0, sizeof(*port));
> > 332 port->addr.client = client->seq_client;
> > 333 port->addr.port = device * (256 / SNDRV_RAWMIDI_DEVICES) + p;
> > 334 port->flags = SNDRV_SEQ_PORT_FLG_GIVEN_PORT;
> > 335 memset(info, 0, sizeof(*info));
> > 336 info->device = device;
> > 337 if (p < output_count)
> > 338 info->stream = SNDRV_RAWMIDI_STREAM_OUTPUT;
> > 339 else
> > 340 info->stream = SNDRV_RAWMIDI_STREAM_INPUT;
> > 341 info->subdevice = p;
> > 342 if (snd_rawmidi_info_select(card, info) >= 0)
> > ^^^^^^^^^^^^^^^^^^^^^^^
> > We can't call this function when we're holding the lock or it leads to
> > a deadlock.
>
> Those two register_mutex are different ones; i.e. both are local static
> variables, hence its scope is only for rawmidi.c and seq_client.c,
> hence they can't conflict with each other.
>
> Or am I missing something else?
>
Ah... Sorry. And I think I just sent you another bogus bug report a
few minutes ago. :/
regards,
dan carpenter
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