static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
				  unsigned int in_interrupt)
{
	struct snd_pcm_runtime *runtime = substream->runtime;
	snd_pcm_uframes_t pos;
	snd_pcm_uframes_t old_hw_ptr, new_hw_ptr, hw_base;
	snd_pcm_sframes_t hdelta, delta;
	unsigned long jdelta;
	unsigned long curr_jiffies;
	struct timespec curr_tstamp;
	struct timespec audio_tstamp;
	int crossed_boundary = 0;

	old_hw_ptr = runtime->status->hw_ptr;

	/*
	 * group pointer, time and jiffies reads to allow for more
	 * accurate correlations/corrections.
	 * The values are stored at the end of this routine after
	 * corrections for hw_ptr position
	 */
	pos = substream->ops->pointer(substream);
	curr_jiffies = jiffies;
	if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE) {
		if ((substream->ops->get_time_info) &&
			(runtime->audio_tstamp_config.type_requested != SNDRV_PCM_AUDIO_TSTAMP_TYPE_DEFAULT)) {
			substream->ops->get_time_info(substream, &curr_tstamp,
						&audio_tstamp,
						&runtime->audio_tstamp_config,
						&runtime->audio_tstamp_report);

			/* re-test in case tstamp type is not supported in hardware and was demoted to DEFAULT */
			if (runtime->audio_tstamp_report.actual_type == SNDRV_PCM_AUDIO_TSTAMP_TYPE_DEFAULT)
				snd_pcm_gettime(runtime, (struct timespec *)&curr_tstamp);
		} else
			snd_pcm_gettime(runtime, (struct timespec *)&curr_tstamp);
	}

	if (pos == SNDRV_PCM_POS_XRUN) {
		xrun(substream);
		return -EPIPE;
	}
	if (pos >= runtime->buffer_size) {
		if (printk_ratelimit()) {
			char name[16];
			snd_pcm_debug_name(substream, name, sizeof(name));
			pcm_err(substream->pcm,
				"invalid position: %s, pos = %ld, buffer size = %ld, period size = %ld\n",
				name, pos, runtime->buffer_size,
				runtime->period_size);
		}
		pos = 0;
	}
	pos -= pos % runtime->min_align;
	trace_hwptr(substream, pos, in_interrupt);
	hw_base = runtime->hw_ptr_base;
	new_hw_ptr = hw_base + pos;
	if (in_interrupt) {
		/* we know that one period was processed */
		/* delta = "expected next hw_ptr" for in_interrupt != 0 */
		delta = runtime->hw_ptr_interrupt + runtime->period_size;
		if (delta > new_hw_ptr) {
			/* check for double acknowledged interrupts */
			hdelta = curr_jiffies - runtime->hw_ptr_jiffies;
			if (hdelta > runtime->hw_ptr_buffer_jiffies/2 + 1) {
				hw_base += runtime->buffer_size;
				if (hw_base >= runtime->boundary) {
					hw_base = 0;
					crossed_boundary++;
				}
				new_hw_ptr = hw_base + pos;
				goto __delta;
			}
		}
	}
	/* new_hw_ptr might be lower than old_hw_ptr in case when */
	/* pointer crosses the end of the ring buffer */
	if (new_hw_ptr < old_hw_ptr) {
		hw_base += runtime->buffer_size;
		if (hw_base >= runtime->boundary) {
			hw_base = 0;
			crossed_boundary++;
		}
		new_hw_ptr = hw_base + pos;
	}
      __delta:
	delta = new_hw_ptr - old_hw_ptr;
	if (delta < 0)
		delta += runtime->boundary;

	if (runtime->no_period_wakeup) {
		snd_pcm_sframes_t xrun_threshold;
		/*
		 * Without regular period interrupts, we have to check
		 * the elapsed time to detect xruns.
		 */
		jdelta = curr_jiffies - runtime->hw_ptr_jiffies;
		if (jdelta < runtime->hw_ptr_buffer_jiffies / 2)
			goto no_delta_check;
		hdelta = jdelta - delta * HZ / runtime->rate;
		xrun_threshold = runtime->hw_ptr_buffer_jiffies / 2 + 1;
		while (hdelta > xrun_threshold) {
			delta += runtime->buffer_size;
			hw_base += runtime->buffer_size;
			if (hw_base >= runtime->boundary) {
				hw_base = 0;
				crossed_boundary++;
			}
			new_hw_ptr = hw_base + pos;
			hdelta -= runtime->hw_ptr_buffer_jiffies;
		}
		goto no_delta_check;
	}

	/* something must be really wrong */
	if (delta >= runtime->buffer_size + runtime->period_size) {
		hw_ptr_error(substream, in_interrupt, "Unexpected hw_ptr",
			     "(stream=%i, pos=%ld, new_hw_ptr=%ld, old_hw_ptr=%ld)\n",
			     substream->stream, (long)pos,
			     (long)new_hw_ptr, (long)old_hw_ptr);
		return 0;
	}

	/* Do jiffies check only in xrun_debug mode */
	if (!xrun_debug(substream, XRUN_DEBUG_JIFFIESCHECK))
		goto no_jiffies_check;

	/* Skip the jiffies check for hardwares with BATCH flag.
	 * Such hardware usually just increases the position at each IRQ,
	 * thus it can't give any strange position.
	 */
	if (runtime->hw.info & SNDRV_PCM_INFO_BATCH)
		goto no_jiffies_check;
	hdelta = delta;
	if (hdelta < runtime->delay)
		goto no_jiffies_check;
	hdelta -= runtime->delay;
	jdelta = curr_jiffies - runtime->hw_ptr_jiffies;
	if (((hdelta * HZ) / runtime->rate) > jdelta + HZ/100) {
		delta = jdelta /
			(((runtime->period_size * HZ) / runtime->rate)
								+ HZ/100);
		/* move new_hw_ptr according jiffies not pos variable */
		new_hw_ptr = old_hw_ptr;
		hw_base = delta;
		/* use loop to avoid checks for delta overflows */
		/* the delta value is small or zero in most cases */
		while (delta > 0) {
			new_hw_ptr += runtime->period_size;
			if (new_hw_ptr >= runtime->boundary) {
				new_hw_ptr -= runtime->boundary;
				crossed_boundary--;
			}
			delta--;
		}
		/* align hw_base to buffer_size */
		hw_ptr_error(substream, in_interrupt, "hw_ptr skipping",
			     "(pos=%ld, delta=%ld, period=%ld, jdelta=%lu/%lu/%lu, hw_ptr=%ld/%ld)\n",
			     (long)pos, (long)hdelta,
			     (long)runtime->period_size, jdelta,
			     ((hdelta * HZ) / runtime->rate), hw_base,
			     (unsigned long)old_hw_ptr,
			     (unsigned long)new_hw_ptr);
		/* reset values to proper state */
		delta = 0;
		hw_base = new_hw_ptr - (new_hw_ptr % runtime->buffer_size);
	}
 no_jiffies_check:
	if (delta > runtime->period_size + runtime->period_size / 2) {
		hw_ptr_error(substream, in_interrupt,
			     "Lost interrupts?",
			     "(stream=%i, delta=%ld, new_hw_ptr=%ld, old_hw_ptr=%ld)\n",
			     substream->stream, (long)delta,
			     (long)new_hw_ptr,
			     (long)old_hw_ptr);
	}

 no_delta_check:
	if (runtime->status->hw_ptr == new_hw_ptr) {
		update_audio_tstamp(substream, &curr_tstamp, &audio_tstamp);
		return 0;
	}

	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
	    runtime->silence_size > 0)
		snd_pcm_playback_silence(substream, new_hw_ptr);

	if (in_interrupt) {
		delta = new_hw_ptr - runtime->hw_ptr_interrupt;
		if (delta < 0)
			delta += runtime->boundary;
		delta -= (snd_pcm_uframes_t)delta % runtime->period_size;
		runtime->hw_ptr_interrupt += delta;
		if (runtime->hw_ptr_interrupt >= runtime->boundary)
			runtime->hw_ptr_interrupt -= runtime->boundary;
	}
	runtime->hw_ptr_base = hw_base;
	runtime->status->hw_ptr = new_hw_ptr;
	runtime->hw_ptr_jiffies = curr_jiffies;
	if (crossed_boundary) {
		snd_BUG_ON(crossed_boundary != 1);
		runtime->hw_ptr_wrap += runtime->boundary;
	}

	update_audio_tstamp(substream, &curr_tstamp, &audio_tstamp);

	return snd_pcm_update_state(substream, runtime);
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.