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[Qemu-devel] [PATCH v4] scsi: lsi: exit infinite loop while executing sc
From: |
P J P |
Subject: |
[Qemu-devel] [PATCH v4] scsi: lsi: exit infinite loop while executing script (CVE-2019-12068) |
Date: |
Wed, 14 Aug 2019 17:35:21 +0530 |
From: Prasad J Pandit <address@hidden>
When executing script in lsi_execute_script(), the LSI scsi adapter
emulator advances 's->dsp' index to read next opcode. This can lead
to an infinite loop if the next opcode is empty. Exit such loop
after 10k iterations.
Reported-by: Bugs SysSec <address@hidden>
Signed-off-by: Prasad J Pandit <address@hidden>
---
hw/scsi/lsi53c895a.c | 41 +++++++++++++++++++++++++++--------------
1 file changed, 27 insertions(+), 14 deletions(-)
Update v4: slightly modify the check and exit
-> https://lists.gnu.org/archive/html/qemu-devel/2019-08/msg02304.html
diff --git a/hw/scsi/lsi53c895a.c b/hw/scsi/lsi53c895a.c
index 10468c1ec1..72f7b59ab5 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 +1135,21 @@ 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);
+ trace_lsi_execute_script_stop();
+ return;
+ }
insn = read_dword(s, s->dsp);
if (!insn) {
/* If we receive an empty opcode increment the DSP by 4 bytes
@@ -1569,19 +1586,7 @@ again:
}
}
}
- if (insn_processed > 10000 && s->waiting == LSI_NOWAIT) {
- /* 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);
- } else if (s->istat1 & LSI_ISTAT1_SRUN && s->waiting == LSI_NOWAIT) {
+ if (s->istat1 & LSI_ISTAT1_SRUN && s->waiting == LSI_NOWAIT) {
if (s->dcntl & LSI_DCNTL_SSM) {
lsi_script_dma_interrupt(s, LSI_DSTAT_SSI);
} else {
@@ -1969,6 +1974,10 @@ static void lsi_reg_writeb(LSIState *s, int offset,
uint8_t val)
case 0x2f: /* DSP[24:31] */
s->dsp &= 0x00ffffff;
s->dsp |= val << 24;
+ /*
+ * FIXME: if s->waiting != LSI_NOWAIT, this will only execute one
+ * instruction. Is this correct?
+ */
if ((s->dmode & LSI_DMODE_MAN) == 0
&& (s->istat1 & LSI_ISTAT1_SRUN) == 0)
lsi_execute_script(s);
@@ -1987,6 +1996,10 @@ static void lsi_reg_writeb(LSIState *s, int offset,
uint8_t val)
break;
case 0x3b: /* DCNTL */
s->dcntl = val & ~(LSI_DCNTL_PFF | LSI_DCNTL_STD);
+ /*
+ * FIXME: if s->waiting != LSI_NOWAIT, this will only execute one
+ * instruction. Is this correct?
+ */
if ((val & LSI_DCNTL_STD) && (s->istat1 & LSI_ISTAT1_SRUN) == 0)
lsi_execute_script(s);
break;
--
2.21.0
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