[PATCH] hw/audio/c97: fix abort in audio_calloc()

[Qiang Liu <cyruscyliu@gmail.com>]

Section 5.10.2 of the AC97 specification (https://hands.com/~lkcl/ac97_r23.pdf)
shows the feasibility to support for rates other than 48kHZ. Specifically,
AC97_PCM_Front_DAC_Rate (reg 2Ch) should be from 8kHZ to 48kHZ.

Before Volker Rümelin fixed it in 12f4abf6a245 and 0cbc8bd4694f, an adversary
could leverage this to crash QEMU.

Fixes: e5c9a13e2670 ("PCI AC97 emulation by malc.")
Reported-by: Volker Rümelin <vr_qemu@t-online.de>
Reported-by: Qiang Liu <cyruscyliu@gmail.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1393
Signed-off-by: Qiang Liu <cyruscyliu@gmail.com>
---
 hw/audio/ac97.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/hw/audio/ac97.c b/hw/audio/ac97.c
index be2dd701a4..826411e462 100644
--- a/hw/audio/ac97.c
+++ b/hw/audio/ac97.c
@@ -625,9 +625,14 @@ static void nam_writew(void *opaque, uint32_t addr, uint32_t val)
         break;
     case AC97_PCM_Front_DAC_Rate:
         if (mixer_load(s, AC97_Extended_Audio_Ctrl_Stat) & EACS_VRA) {
-            mixer_store(s, addr, val);
-            dolog("Set front DAC rate to %d\n", val);
-            open_voice(s, PO_INDEX, val);
+            if (val >= 8000 && val <= 48000) {
+                mixer_store(s, addr, val);
+                dolog("Set front DAC rate to %d\n", val);
+                open_voice(s, PO_INDEX, val);
+            } else {
+                dolog("Attempt to set front DAC rate to %d, but valid is"
+                      "8-48kHZ\n", val);
+            }
         } else {
             dolog("Attempt to set front DAC rate to %d, but VRA is not set\n",
                   val);
-- 
2.25.1