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

[Bernhard Beschow]

Am 25. Dezember 2022 12:13:57 UTC schrieb 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);

We probably want to log a guest error here. Not only does this communicate 
clearly where the problem is (-> in guest code) but it is also incredibly 
useful for development (think of reusing this code in other device models such 
as vt82c686b if applicable).

Best regards,
Bernhard

>+            }
>         } else {
>             dolog("Attempt to set front DAC rate to %d, but VRA is not set\n",
>                   val);