* [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
@ 2016-09-03 6:33 P J P
2016-09-05 9:04 ` Paolo Bonzini
0 siblings, 1 reply; 9+ messages in thread
From: P J P @ 2016-09-03 6:33 UTC (permalink / raw)
To: Qemu Developers; +Cc: Dmitry Fleytman, Paolo Bonzini, Li Qiang, Prasad J Pandit
From: Prasad J Pandit <pjp@fedoraproject.org>
In PVSCSI paravirtual SCSI bus, the request descriptor data
length is defined to be 64 bit. While building SG list from
a request descriptor, it gets truncated to 32bit in routine
'pvscsi_convert_sglist'. This could lead to an infinite loop
situation for arbitrarily large 'dataLen' values. Define local
variable 'data_length' to be 32 bit, to avoid it.
Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
hw/scsi/vmw_pvscsi.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/hw/scsi/vmw_pvscsi.c b/hw/scsi/vmw_pvscsi.c
index 4245c15..4d38330 100644
--- a/hw/scsi/vmw_pvscsi.c
+++ b/hw/scsi/vmw_pvscsi.c
@@ -629,7 +629,7 @@ static void
pvscsi_convert_sglist(PVSCSIRequest *r)
{
int chunk_size;
- uint64_t data_length = r->req.dataLen;
+ uint32_t data_length = r->req.dataLen;
PVSCSISGState sg = r->sg;
while (data_length) {
while (!sg.resid) {
@@ -637,8 +637,7 @@ pvscsi_convert_sglist(PVSCSIRequest *r)
trace_pvscsi_convert_sglist(r->req.context, r->sg.dataAddr,
r->sg.resid);
}
- assert(data_length > 0);
- chunk_size = MIN((unsigned) data_length, sg.resid);
+ chunk_size = MIN(data_length, sg.resid);
if (chunk_size) {
qemu_sglist_add(&r->sgl, sg.dataAddr, chunk_size);
}
--
2.5.5
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
2016-09-03 6:33 [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit P J P
@ 2016-09-05 9:04 ` Paolo Bonzini
2016-09-05 9:50 ` P J P
0 siblings, 1 reply; 9+ messages in thread
From: Paolo Bonzini @ 2016-09-05 9:04 UTC (permalink / raw)
To: P J P, Qemu Developers; +Cc: Dmitry Fleytman, Li Qiang, Prasad J Pandit
On 03/09/2016 08:33, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> In PVSCSI paravirtual SCSI bus, the request descriptor data
> length is defined to be 64 bit. While building SG list from
> a request descriptor, it gets truncated to 32bit in routine
> 'pvscsi_convert_sglist'. This could lead to an infinite loop
> situation for arbitrarily large 'dataLen' values. Define local
> variable 'data_length' to be 32 bit, to avoid it.
>
> Reported-by: Li Qiang <liqiang6-s@360.cn>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
> hw/scsi/vmw_pvscsi.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/hw/scsi/vmw_pvscsi.c b/hw/scsi/vmw_pvscsi.c
> index 4245c15..4d38330 100644
> --- a/hw/scsi/vmw_pvscsi.c
> +++ b/hw/scsi/vmw_pvscsi.c
> @@ -629,7 +629,7 @@ static void
> pvscsi_convert_sglist(PVSCSIRequest *r)
> {
> int chunk_size;
> - uint64_t data_length = r->req.dataLen;
> + uint32_t data_length = r->req.dataLen;
Why is this needed if you remove the cast in MIN, below?
Paolo
> PVSCSISGState sg = r->sg;
> while (data_length) {
> while (!sg.resid) {
> @@ -637,8 +637,7 @@ pvscsi_convert_sglist(PVSCSIRequest *r)
> trace_pvscsi_convert_sglist(r->req.context, r->sg.dataAddr,
> r->sg.resid);
> }
> - assert(data_length > 0);
> - chunk_size = MIN((unsigned) data_length, sg.resid);
> + chunk_size = MIN(data_length, sg.resid);
> if (chunk_size) {
> qemu_sglist_add(&r->sgl, sg.dataAddr, chunk_size);
> }
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
2016-09-05 9:04 ` Paolo Bonzini
@ 2016-09-05 9:50 ` P J P
2016-09-05 10:00 ` Paolo Bonzini
0 siblings, 1 reply; 9+ messages in thread
From: P J P @ 2016-09-05 9:50 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Qemu Developers, Dmitry Fleytman, Li Qiang
Hello Paolo, all
+-- On Mon, 5 Sep 2016, Paolo Bonzini wrote --+
| > - uint64_t data_length = r->req.dataLen;
| > + uint32_t data_length = r->req.dataLen;
|
| Why is this needed if you remove the cast in MIN, below?
The outer while loop below is controlled by 'data_length'. The cast in MIN
truncates a large(64bit) value of 'data_length' to zero(0), thus setting
'chunk_size' to zero, which results in infinite loop as 'data_length' remains
unchanged(> 0).
Second, Removing cast below results in 'chunk_size' being set to 'sg.resid',
for large(>32bit) values of 'data_length'. Which results in an infinite loop
because the inner 'while(!sg.resid)' loop takes forever to read non-zero
values into 'sg.resid'.
Above type change ensures that outer while loop is not entered if
'data_length' is zero. And removing cast ensures that inner while(!sg.resid)
loop does not have run forever, ie. till large(64 bit) 'data_length' becomes
zero.
Looking at the 'vmw_pvscsi.c' Linux kernel driver, 'dataLen' seems to be set
to an unsigned 32 bit 'bufflen' value.
| > PVSCSISGState sg = r->sg;
| > while (data_length) {
| > while (!sg.resid) {
| > @@ -637,8 +637,7 @@ pvscsi_convert_sglist(PVSCSIRequest *r)
| > trace_pvscsi_convert_sglist(r->req.context, r->sg.dataAddr,
| > r->sg.resid);
| > }
| > - assert(data_length > 0);
| > - chunk_size = MIN((unsigned) data_length, sg.resid);
| > + chunk_size = MIN(data_length, sg.resid);
| > if (chunk_size) {
| > qemu_sglist_add(&r->sgl, sg.dataAddr, chunk_size);
| > }
| >
|
Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
2016-09-05 9:50 ` P J P
@ 2016-09-05 10:00 ` Paolo Bonzini
2016-09-05 11:13 ` P J P
0 siblings, 1 reply; 9+ messages in thread
From: Paolo Bonzini @ 2016-09-05 10:00 UTC (permalink / raw)
To: P J P; +Cc: Qemu Developers, Dmitry Fleytman, Li Qiang
On 05/09/2016 11:50, P J P wrote:
> Hello Paolo, all
>
> +-- On Mon, 5 Sep 2016, Paolo Bonzini wrote --+
> | > - uint64_t data_length = r->req.dataLen;
> | > + uint32_t data_length = r->req.dataLen;
> |
> | Why is this needed if you remove the cast in MIN, below?
>
> The outer while loop below is controlled by 'data_length'. The cast in MIN
> truncates a large(64bit) value of 'data_length' to zero(0), thus setting
> 'chunk_size' to zero, which results in infinite loop as 'data_length' remains
> unchanged(> 0).
>
> Second, Removing cast below results in 'chunk_size' being set to 'sg.resid',
> for large(>32bit) values of 'data_length'. Which results in an infinite loop
> because the inner 'while(!sg.resid)' loop takes forever to read non-zero
> values into 'sg.resid'.
No, that's not what happens. chunk_size is set to sg.resid, after which:
sg.dataAddr += chunk_size;
data_length -= chunk_size;
sg.resid -= chunk_size;
The loop is reentered with sg.resid == 0, it calls into
pvscsi_get_next_sg_elem and this sets sg.resid to a nonzero value. It's
not an infinite loop.
> Above type change ensures that outer while loop is not entered if
> 'data_length' is zero. And removing cast ensures that inner while(!sg.resid)
> loop does not have run forever, ie. till large(64 bit) 'data_length' becomes
> zero.
>
> Looking at the 'vmw_pvscsi.c' Linux kernel driver, 'dataLen' seems to be set
> to an unsigned 32 bit 'bufflen' value.
The driver is irrelevant. If the data_length is an uint64_t you need to
ensure that a 64 bit buffer is processed correctly. Here you are
truncating it, which is wrong and will cause a buffer underrun.
Paolo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
2016-09-05 10:00 ` Paolo Bonzini
@ 2016-09-05 11:13 ` P J P
2016-09-05 11:39 ` Paolo Bonzini
0 siblings, 1 reply; 9+ messages in thread
From: P J P @ 2016-09-05 11:13 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Qemu Developers, Dmitry Fleytman, Li Qiang
+-- On Mon, 5 Sep 2016, Paolo Bonzini wrote --+
| No, that's not what happens. chunk_size is set to sg.resid, after which:
|
| sg.dataAddr += chunk_size;
| data_length -= chunk_size;
| sg.resid -= chunk_size;
|
| The loop is reentered with sg.resid == 0, it calls into
| pvscsi_get_next_sg_elem and this sets sg.resid to a nonzero value. It's
| not an infinite loop.
Yes, true; But 'pvscsi_get_next_sg_elem' does not return non-zero 'sg.resid'
each time. In fact, it returns more zeros and thus the loop iterates
infinitely. When I ran it with 64 bit 'data_length' and without cast, after
some time, the inner loop gets stuck and does not seem to read non-zero values
into 'sg.resid'.
Is there limit to number of SG elements?
| The driver is irrelevant. If the data_length is an uint64_t you need to
| ensure that a 64 bit buffer is processed correctly. Here you are
| truncating it, which is wrong and will cause a buffer underrun.
Yes. I thought truncation in MIN was intentional, considering the driver
sets 'dataLen' to 32 bit value.
If we are to go with 64 bit 'data_length', how long should the inner while
loop run?
Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
2016-09-05 11:13 ` P J P
@ 2016-09-05 11:39 ` Paolo Bonzini
2016-09-05 12:58 ` P J P
0 siblings, 1 reply; 9+ messages in thread
From: Paolo Bonzini @ 2016-09-05 11:39 UTC (permalink / raw)
To: P J P; +Cc: Qemu Developers, Dmitry Fleytman, Li Qiang
On 05/09/2016 13:13, P J P wrote:
> +-- On Mon, 5 Sep 2016, Paolo Bonzini wrote --+
> | No, that's not what happens. chunk_size is set to sg.resid, after which:
> |
> | sg.dataAddr += chunk_size;
> | data_length -= chunk_size;
> | sg.resid -= chunk_size;
> |
> | The loop is reentered with sg.resid == 0, it calls into
> | pvscsi_get_next_sg_elem and this sets sg.resid to a nonzero value. It's
> | not an infinite loop.
>
> Yes, true; But 'pvscsi_get_next_sg_elem' does not return non-zero 'sg.resid'
> each time. In fact, it returns more zeros and thus the loop iterates
> infinitely. When I ran it with 64 bit 'data_length' and without cast, after
> some time, the inner loop gets stuck and does not seem to read non-zero values
> into 'sg.resid'.
pvscsi_get_next_sg_elem just reads 16 bytes from guest RAM, so I guess
that's because you didn't set up the SG list correctly. QEMU indeed
doesn't check for that, but that's a different bug.
> Is there limit to number of SG elements?
Without a public spec it's hard, but I guess 2048 is more than enough.
Paolo
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
2016-09-05 11:39 ` Paolo Bonzini
@ 2016-09-05 12:58 ` P J P
2016-09-05 13:02 ` Paolo Bonzini
0 siblings, 1 reply; 9+ messages in thread
From: P J P @ 2016-09-05 12:58 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Qemu Developers, Dmitry Fleytman, Li Qiang
+-- On Mon, 5 Sep 2016, Paolo Bonzini wrote --+
| Without a public spec it's hard, but I guess 2048 is more than enough.
===
diff --git a/hw/scsi/vmw_pvscsi.c b/hw/scsi/vmw_pvscsi.c
index 4245c15..4823b9d 100644
--- a/hw/scsi/vmw_pvscsi.c
+++ b/hw/scsi/vmw_pvscsi.c
@@ -628,17 +628,16 @@ pvscsi_queue_pending_descriptor(PVSCSIState *s, SCSIDevice **d,
static void
pvscsi_convert_sglist(PVSCSIRequest *r)
{
- int chunk_size;
+ int chunk_size, n = 0;
uint64_t data_length = r->req.dataLen;
PVSCSISGState sg = r->sg;
- while (data_length) {
- while (!sg.resid) {
+ while (data_length && n < 2048) {
+ while (!sg.resid && n++ < 2048) {
pvscsi_get_next_sg_elem(&sg);
trace_pvscsi_convert_sglist(r->req.context, r->sg.dataAddr,
r->sg.resid);
}
- assert(data_length > 0);
- chunk_size = MIN((unsigned) data_length, sg.resid);
+ chunk_size = MIN(data_length, sg.resid);
if (chunk_size) {
qemu_sglist_add(&r->sgl, sg.dataAddr, chunk_size);
}
===
Does this look okay?
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
2016-09-05 12:58 ` P J P
@ 2016-09-05 13:02 ` Paolo Bonzini
2016-09-05 20:52 ` P J P
0 siblings, 1 reply; 9+ messages in thread
From: Paolo Bonzini @ 2016-09-05 13:02 UTC (permalink / raw)
To: P J P; +Cc: Qemu Developers, Dmitry Fleytman, Li Qiang
On 05/09/2016 14:58, P J P wrote:
> +-- On Mon, 5 Sep 2016, Paolo Bonzini wrote --+
> | Without a public spec it's hard, but I guess 2048 is more than enough.
>
> ===
> diff --git a/hw/scsi/vmw_pvscsi.c b/hw/scsi/vmw_pvscsi.c
> index 4245c15..4823b9d 100644
> --- a/hw/scsi/vmw_pvscsi.c
> +++ b/hw/scsi/vmw_pvscsi.c
> @@ -628,17 +628,16 @@ pvscsi_queue_pending_descriptor(PVSCSIState *s, SCSIDevice **d,
> static void
> pvscsi_convert_sglist(PVSCSIRequest *r)
> {
> - int chunk_size;
> + int chunk_size, n = 0;
chunk_size should be uint32_t.
> uint64_t data_length = r->req.dataLen;
> PVSCSISGState sg = r->sg;
> - while (data_length) {
> - while (!sg.resid) {
> + while (data_length && n < 2048) {
> + while (!sg.resid && n++ < 2048) {
> pvscsi_get_next_sg_elem(&sg);
> trace_pvscsi_convert_sglist(r->req.context, r->sg.dataAddr,
> r->sg.resid);
> }
> - assert(data_length > 0);
> - chunk_size = MIN((unsigned) data_length, sg.resid);
> + chunk_size = MIN(data_length, sg.resid);
> if (chunk_size) {
> qemu_sglist_add(&r->sgl, sg.dataAddr, chunk_size);
> }
> ===
>
> Does this look okay?
Yes, just change 2048 to a #define PVSCSI_MAX_SG_ELEM.
Paolo
> --
> Prasad J Pandit / Red Hat Product Security Team
> 47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit
2016-09-05 13:02 ` Paolo Bonzini
@ 2016-09-05 20:52 ` P J P
0 siblings, 0 replies; 9+ messages in thread
From: P J P @ 2016-09-05 20:52 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Qemu Developers, Dmitry Fleytman, Li Qiang
+-- On Mon, 5 Sep 2016, Paolo Bonzini wrote --+
| chunk_size should be uint32_t.
|
| > - while (data_length) {
| > - while (!sg.resid) {
| > + while (data_length && n < 2048) {
| > + while (!sg.resid && n++ < 2048) {
| > pvscsi_get_next_sg_elem(&sg);
| > - assert(data_length > 0);
| > - chunk_size = MIN((unsigned) data_length, sg.resid);
| > + chunk_size = MIN(data_length, sg.resid);
| > Does this look okay?
|
| Yes, just change 2048 to a #define PVSCSI_MAX_SG_ELEM.
Done. I've sent a revised patch v2.
Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2016-09-05 20:52 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-09-03 6:33 [Qemu-devel] [PATCH] scsi: pvscsi: request descriptor data_length to 32 bit P J P
2016-09-05 9:04 ` Paolo Bonzini
2016-09-05 9:50 ` P J P
2016-09-05 10:00 ` Paolo Bonzini
2016-09-05 11:13 ` P J P
2016-09-05 11:39 ` Paolo Bonzini
2016-09-05 12:58 ` P J P
2016-09-05 13:02 ` Paolo Bonzini
2016-09-05 20:52 ` P J P
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