1. Patchew
  2. QEMU
  3. [PATCH v2 0/3] Megasas: fix OOB access and NULL dereference issues
  4. View patch

[PATCH v2 2/3] megasas: avoid NULL pointer dereference

P J P posted 3 patches 5 years, 9 months ago
Maintainers: Fam Zheng <fam@euphon.net>, Hannes Reinecke <hare@suse.com>, Paolo Bonzini <pbonzini@redhat.com>
[PATCH v2 2/3] megasas: avoid NULL pointer dereference
Posted by P J P 5 years, 9 months ago 
From: Prasad J Pandit <pjp@fedoraproject.org>

While in megasas_handle_frame(), megasas_enqueue_frame() may
set a NULL frame into MegasasCmd object for a given 'frame_addr'
address. Add check to avoid a NULL pointer dereference issue.

Reported-by: Alexander Bulekov <alxndr@bu.edu>
Fixes: https://bugs.launchpad.net/qemu/+bug/1878259
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/scsi/megasas.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
index 6ce598cd69..b531d88a9b 100644
--- a/hw/scsi/megasas.c
+++ b/hw/scsi/megasas.c
@@ -504,7 +504,7 @@ static MegasasCmd *megasas_enqueue_frame(MegasasState *s,
     cmd->pa = frame;
     /* Map all possible frames */
     cmd->frame = pci_dma_map(pcid, frame, &frame_size_p, 0);
-    if (frame_size_p != frame_size) {
+    if (!cmd->frame || frame_size_p != frame_size) {
         trace_megasas_qf_map_failed(cmd->index, (unsigned long)frame);
         if (cmd->frame) {
             megasas_unmap_frame(s, cmd);
-- 
2.25.4
Re: [PATCH v2 2/3] megasas: avoid NULL pointer dereference
Posted by Paolo Bonzini 5 years, 8 months ago 
On 13/05/20 21:25, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While in megasas_handle_frame(), megasas_enqueue_frame() may
> set a NULL frame into MegasasCmd object for a given 'frame_addr'
> address. Add check to avoid a NULL pointer dereference issue.
> 
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Fixes: https://bugs.launchpad.net/qemu/+bug/1878259
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/scsi/megasas.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
> index 6ce598cd69..b531d88a9b 100644
> --- a/hw/scsi/megasas.c
> +++ b/hw/scsi/megasas.c
> @@ -504,7 +504,7 @@ static MegasasCmd *megasas_enqueue_frame(MegasasState *s,
>      cmd->pa = frame;
>      /* Map all possible frames */
>      cmd->frame = pci_dma_map(pcid, frame, &frame_size_p, 0);
> -    if (frame_size_p != frame_size) {
> +    if (!cmd->frame || frame_size_p != frame_size) {
>          trace_megasas_qf_map_failed(cmd->index, (unsigned long)frame);
>          if (cmd->frame) {
>              megasas_unmap_frame(s, cmd);
> -- 2.25.4
> 

I think the code here was expecting frame_size_p to be 0 if cmd->frame
is NULL.  Can you check why this is not the case, or whether it ever was
the case?

Thanks,

Paolo
Re: [PATCH v2 2/3] megasas: avoid NULL pointer dereference
Posted by P J P 5 years, 8 months ago 
  Hello,

+-- On Thu, 21 May 2020, Paolo Bonzini wrote --+
| I think the code here was expecting frame_size_p to be 0 if cmd->frame is 
| NULL.  Can you check why this is not the case, or whether it ever was the 
| case?

static MegasasCmd *megasas_enqueue_frame(MegasasState *s, hwaddr frame,
    ...
    int frame_size = MEGASAS_MAX_SGE * sizeof(union mfi_sgl);                   
    hwaddr frame_size_p = frame_size;  <== = 128 * 16 = 2048

so 'frame_size_p' always starts with value '2048'

    ...
    cmd->frame = pci_dma_map(pcid, frame, &frame_size_p, 0);
     -> pci_dma_map
      -> dma_memory_map
       -> address_space_map
          mr = flatview_translate(fv, addr, &xlat, &l, is_write, attrs);
          ...
          if (atomic_xchg(&bounce.in_use, true)) {
              return NULL;    <== NULL is returned from here
          }

Later when address_space_map() returns 'NULL' above, '*plen' is not set to 
zero.

diff --git a/exec.c b/exec.c
index 5162f0d12f..4eea84bf66 100644
--- a/exec.c
+++ b/exec.c
@@ -3538,6 +3538,7 @@ void *address_space_map(AddressSpace *as,
 
     if (!memory_access_is_direct(mr, is_write)) {
         if (atomic_xchg(&bounce.in_use, true)) {
+            *plen = 0;
             return NULL;
         }

I'll send a revised patch above.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D
Re: [PATCH v2 2/3] megasas: avoid NULL pointer dereference
Posted by Paolo Bonzini 5 years, 8 months ago 
On 26/05/20 09:18, P J P wrote:
> Later when address_space_map() returns 'NULL' above, '*plen' is not set to 
> zero.
> 
> diff --git a/exec.c b/exec.c
> index 5162f0d12f..4eea84bf66 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -3538,6 +3538,7 @@ void *address_space_map(AddressSpace *as,
>  
>      if (!memory_access_is_direct(mr, is_write)) {
>          if (atomic_xchg(&bounce.in_use, true)) {
> +            *plen = 0;
>              return NULL;
>          }
> 
> I'll send a revised patch above.

Great, this looks good.

Paolo
Re: [PATCH v2 2/3] megasas: avoid NULL pointer dereference
Posted by Darren Kenny 5 years, 9 months ago 
On Thursday, 2020-05-14 at 00:55:39 +0530, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> While in megasas_handle_frame(), megasas_enqueue_frame() may
> set a NULL frame into MegasasCmd object for a given 'frame_addr'
> address. Add check to avoid a NULL pointer dereference issue.
>
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Fixes: https://bugs.launchpad.net/qemu/+bug/1878259
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>

Reviewed-by: Darren Kenny <darren.kenny@oracle.com>

> ---
>  hw/scsi/megasas.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
> index 6ce598cd69..b531d88a9b 100644
> --- a/hw/scsi/megasas.c
> +++ b/hw/scsi/megasas.c
> @@ -504,7 +504,7 @@ static MegasasCmd *megasas_enqueue_frame(MegasasState *s,
>      cmd->pa = frame;
>      /* Map all possible frames */
>      cmd->frame = pci_dma_map(pcid, frame, &frame_size_p, 0);
> -    if (frame_size_p != frame_size) {
> +    if (!cmd->frame || frame_size_p != frame_size) {
>          trace_megasas_qf_map_failed(cmd->index, (unsigned long)frame);
>          if (cmd->frame) {
>              megasas_unmap_frame(s, cmd);
> -- 
> 2.25.4
Re: [PATCH v2 2/3] megasas: avoid NULL pointer dereference
Posted by Alexander Bulekov 5 years, 9 months ago 
On 200514 0055, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While in megasas_handle_frame(), megasas_enqueue_frame() may
> set a NULL frame into MegasasCmd object for a given 'frame_addr'
> address. Add check to avoid a NULL pointer dereference issue.
> 
> Reported-by: Alexander Bulekov <alxndr@bu.edu>
> Fixes: https://bugs.launchpad.net/qemu/+bug/1878259
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>

Acked-by: Alexander Bulekov <alxndr@bu.edu>

> ---
>  hw/scsi/megasas.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
> index 6ce598cd69..b531d88a9b 100644
> --- a/hw/scsi/megasas.c
> +++ b/hw/scsi/megasas.c
> @@ -504,7 +504,7 @@ static MegasasCmd *megasas_enqueue_frame(MegasasState *s,
>      cmd->pa = frame;
>      /* Map all possible frames */
>      cmd->frame = pci_dma_map(pcid, frame, &frame_size_p, 0);
> -    if (frame_size_p != frame_size) {
> +    if (!cmd->frame || frame_size_p != frame_size) {
>          trace_megasas_qf_map_failed(cmd->index, (unsigned long)frame);
>          if (cmd->frame) {
>              megasas_unmap_frame(s, cmd);
> -- 
> 2.25.4
>

Patchew 2.1-devel-b67e4c2

© 2016 - 2026 Red Hat, Inc.