[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH v3 1/2] scsi: lsi: exit infinite loop while exec
From: |
P J P |
Subject: |
Re: [Qemu-devel] [PATCH v3 1/2] scsi: lsi: exit infinite loop while executing script (CVE-2019-12068) |
Date: |
Wed, 14 Aug 2019 15:55:41 +0530 (IST) |
+-- On Tue, 13 Aug 2019, Paolo Bonzini wrote --+
| After the first instruction is processed, "again" is only reached if
| s->waiting == LSI_NOWAIT. Therefore, we could move the Windows hack to the
| beginning and remove the s->waiting condition. The only change would be
| that it would also be triggered by all zero instructions, like this:
|
| diff --git a/hw/scsi/lsi53c895a.c b/hw/scsi/lsi53c895a.c
| index 10468c1..9d714af 100644
| --- a/hw/scsi/lsi53c895a.c
| +++ b/hw/scsi/lsi53c895a.c
| @@ -185,6 +185,9 @@ static const char *names[] = {
| /* Flag set if this is a tagged command. */
| #define LSI_TAG_VALID (1 << 16)
|
| +/* Maximum instructions to process. */
| +#define LSI_MAX_INSN 10000
| +
| typedef struct lsi_request {
| SCSIRequest *req;
| uint32_t tag;
| @@ -1132,7 +1135,19 @@ static void lsi_execute_script(LSIState *s)
|
| s->istat1 |= LSI_ISTAT1_SRUN;
| again:
| - insn_processed++;
| + if (++insn_processed > LSI_MAX_INSN) {
| + /* Some windows drivers make the device spin waiting for a memory
| + location to change. If we have been executed a lot of code then
| + assume this is the case and force an unexpected device disconnect.
| + This is apparently sufficient to beat the drivers into submission.
| + */
| + if (!(s->sien0 & LSI_SIST0_UDC)) {
| + qemu_log_mask(LOG_GUEST_ERROR,
| + "lsi_scsi: inf. loop with UDC masked");
| + }
| + lsi_script_scsi_interrupt(s, LSI_SIST0_UDC, 0);
| + lsi_disconnect(s);
...
|
| Does it make sense?
Yes, this'd also work, but need to return after lsi_disconnect(s), otherwise
loop would continue.
Should I send a revised patch? (with above change)
Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
[Qemu-devel] [PATCH v3 2/2] scsi: lsi: use macro LSI_MAX_INSN instead of a magic number, P J P, 2019/08/09