hw/audio/sb16: Avoid assertion by restricting I/O sampling rate range

While the SB16 seems to work up to 48000 Hz, the "Sound Blaster Series
Hardware Programming Guide" limit the sampling range from 4000 Hz to
44100 Hz (Section 3-9, 3-10: Digitized Sound I/O Programming, tables
3-2 and 3-3).

Later, section 6-15 (DSP Commands) is more specific regarding the 41h /
42h registers (Set digitized sound output sampling rate):

  Valid sampling rates range from 5000 to 45000 Hz inclusive.

There is no comment regarding error handling if the register is filled
with an out-of-range value.  (See also section 3-28 "8-bit or 16-bit
Auto-initialize Transfer"). Assume limits are enforced in hardware.

This fixes triggering an assertion in audio_calloc():

  #1 abort
  #2 audio_bug audio/audio.c:119:9
  #3 audio_calloc audio/audio.c:154:9
  #4 audio_pcm_sw_alloc_resources_out audio/audio_template.h:116:15
  #5 audio_pcm_sw_init_out audio/audio_template.h:175:11
  #6 audio_pcm_create_voice_pair_out audio/audio_template.h:410:9
  #7 AUD_open_out audio/audio_template.h:503:14
  #8 continue_dma8 hw/audio/sb16.c:216:20
  #9 dma_cmd8 hw/audio/sb16.c:276:5
  #10 command hw/audio/sb16.c:0
  #11 dsp_write hw/audio/sb16.c:949:13
  #12 portio_write softmmu/ioport.c:205:13
  #13 memory_region_write_accessor softmmu/memory.c:491:5
  #14 access_with_adjusted_size softmmu/memory.c:552:18
  #15 memory_region_dispatch_write softmmu/memory.c:0:13
  #16 flatview_write_continue softmmu/physmem.c:2759:23
  #17 flatview_write softmmu/physmem.c:2799:14
  #18 address_space_write softmmu/physmem.c:2891:18
  #19 cpu_outw softmmu/ioport.c:70:5

[*] http://www.baudline.com/solutions/full_duplex/sb16_pci/index.html

OSS-Fuzz Report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=29174

Fixes: 85571bc741 ("audio merge (malc)")
Buglink: https://bugs.launchpad.net/bugs/1910603
Tested-by: Qiang Liu <cyruscyliu@gmail.com>
Reviewed-by: Qiang Liu <cyruscyliu@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210616104349.2398060-1-f4bug@amsat.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

MAINTAINERS

@@ -2221,6 +2221,7 @@ F: qapi/audio.json
 F: tests/qtest/ac97-test.c
 F: tests/qtest/es1370-test.c
 F: tests/qtest/intel-hda-test.c
+F: tests/qtest/fuzz-sb16-test.c
 
 Block layer core
 M: Kevin Wolf <kwolf@redhat.com>

hw/audio/sb16.c

@@ -115,6 +115,9 @@ struct SB16State {
     PortioList portio_list;
 };
 
+#define SAMPLE_RATE_MIN 5000
+#define SAMPLE_RATE_MAX 45000
+
 static void SB_audio_callback (void *opaque, int free);
 
 static int magic_of_irq (int irq)
@@ -241,6 +244,17 @@ static void dma_cmd8 (SB16State *s, int mask, int dma_len)
         int tmp = (256 - s->time_const);
         s->freq = (1000000 + (tmp / 2)) / tmp;
     }
+    if (s->freq < SAMPLE_RATE_MIN) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "sampling range too low: %d, increasing to %u\n",
+                      s->freq, SAMPLE_RATE_MIN);
+        s->freq = SAMPLE_RATE_MIN;
+    } else if (s->freq > SAMPLE_RATE_MAX) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "sampling range too high: %d, decreasing to %u\n",
+                      s->freq, SAMPLE_RATE_MAX);
+        s->freq = SAMPLE_RATE_MAX;
+    }
 
     if (dma_len != -1) {
         s->block_size = dma_len << s->fmt_stereo;

tests/qtest/fuzz-sb16-test.c

@@ -0,0 +1,52 @@
+/*
+ * QTest fuzzer-generated testcase for sb16 audio device
+ *
+ * Copyright (c) 2021 Philippe Mathieu-Daudé <f4bug@amsat.org>
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "libqos/libqtest.h"
+
+/*
+ * This used to trigger the assert in audio_calloc
+ * https://bugs.launchpad.net/qemu/+bug/1910603
+ */
+static void test_fuzz_sb16_0x1c(void)
+{
+    QTestState *s = qtest_init("-M q35 -display none "
+                               "-device sb16,audiodev=snd0 "
+                               "-audiodev none,id=snd0");
+    qtest_outw(s, 0x22c, 0x41);
+    qtest_outb(s, 0x22c, 0x00);
+    qtest_outw(s, 0x22c, 0x1004);
+    qtest_outw(s, 0x22c, 0x001c);
+    qtest_quit(s);
+}
+
+static void test_fuzz_sb16_0x91(void)
+{
+    QTestState *s = qtest_init("-M pc -display none "
+                               "-device sb16,audiodev=none "
+                               "-audiodev id=none,driver=none");
+    qtest_outw(s, 0x22c, 0xf141);
+    qtest_outb(s, 0x22c, 0x00);
+    qtest_outb(s, 0x22c, 0x24);
+    qtest_outb(s, 0x22c, 0x91);
+    qtest_quit(s);
+}
+
+int main(int argc, char **argv)
+{
+    const char *arch = qtest_get_arch();
+
+    g_test_init(&argc, &argv, NULL);
+
+   if (strcmp(arch, "i386") == 0) {
+        qtest_add_func("fuzz/test_fuzz_sb16/1c", test_fuzz_sb16_0x1c);
+        qtest_add_func("fuzz/test_fuzz_sb16/91", test_fuzz_sb16_0x91);
+   }
+
+   return g_test_run();
+}

tests/qtest/meson.build

@@ -20,6 +20,7 @@ slow_qtests = {
 qtests_generic = \
   (config_all_devices.has_key('CONFIG_MEGASAS_SCSI_PCI') ? ['fuzz-megasas-test'] : []) + \
   (config_all_devices.has_key('CONFIG_VIRTIO_SCSI') ? ['fuzz-virtio-scsi-test'] : []) + \
+  (config_all_devices.has_key('CONFIG_SB16') ? ['fuzz-sb16-test'] : []) + \
   [
   'cdrom-test',
   'device-introspect-test',