[PATCH] hw/ide: check null block pointer before blk_drain

[PATCH] hw/ide: check null block pointer before blk_drain

[P J P]

From: Prasad J Pandit <pjp@fedoraproject.org>

While cancelling an i/o operation via ide_cancel_dma_sync(),
check for null block pointer before calling blk_drain(). Avoid
null pointer dereference.

 -> https://ruhr-uni-bochum.sciebo.de/s/NNWP2GfwzYKeKwE?path=%2Fide_nullptr1
    ==1803100==Hint: address points to the zero page.
    #0 blk_bs ../block/block-backend.c:714
    #1 blk_drain ../block/block-backend.c:1715
    #2 ide_cancel_dma_sync ../hw/ide/core.c:723
    #3 bmdma_cmd_writeb ../hw/ide/pci.c:298
    #4 bmdma_write ../hw/ide/piix.c:75
    #5 memory_region_write_accessor ../softmmu/memory.c:483
    #6 access_with_adjusted_size ../softmmu/memory.c:544
    #7 memory_region_dispatch_write ../softmmu/memory.c:1465
    #8 flatview_write_continue ../exec.c:3176
    ...

Reported-by: Ruhr-University <bugs-syssec@rub.de>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/ide/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/ide/core.c b/hw/ide/core.c
index d997a78e47..038af1cd6b 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -718,7 +718,7 @@ void ide_cancel_dma_sync(IDEState *s)
      * whole DMA operation will be submitted to disk with a single
      * aio operation with preadv/pwritev.
      */
-    if (s->bus->dma->aiocb) {
+    if (s->blk && s->bus->dma->aiocb) {
         trace_ide_cancel_dma_sync_remaining();
         blk_drain(s->blk);
         assert(s->bus->dma->aiocb == NULL);
-- 
2.26.2

Re: [PATCH] hw/ide: check null block pointer before blk_drain

[Philippe Mathieu-Daudé]

[-- Attachment #1: Type: text/plain, Size: 1811 bytes --]

Le jeu. 27 août 2020 13:47, P J P <ppandit@redhat.com> a écrit :

> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> While cancelling an i/o operation via ide_cancel_dma_sync(),
> check for null block pointer before calling blk_drain(). Avoid
> null pointer dereference.
>
>  ->
> https://ruhr-uni-bochum.sciebo.de/s/NNWP2GfwzYKeKwE?path=%2Fide_nullptr1
>     ==1803100==Hint: address points to the zero page.
>     #0 blk_bs ../block/block-backend.c:714
>     #1 blk_drain ../block/block-backend.c:1715
>     #2 ide_cancel_dma_sync ../hw/ide/core.c:723
>     #3 bmdma_cmd_writeb ../hw/ide/pci.c:298
>     #4 bmdma_write ../hw/ide/piix.c:75
>     #5 memory_region_write_accessor ../softmmu/memory.c:483
>     #6 access_with_adjusted_size ../softmmu/memory.c:544
>     #7 memory_region_dispatch_write ../softmmu/memory.c:1465
>     #8 flatview_write_continue ../exec.c:3176
>     ...
>
> Reported-by: Ruhr-University <bugs-syssec@rub.de>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/ide/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index d997a78e47..038af1cd6b 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -718,7 +718,7 @@ void ide_cancel_dma_sync(IDEState *s)
>       * whole DMA operation will be submitted to disk with a single
>       * aio operation with preadv/pwritev.
>       */
> -    if (s->bus->dma->aiocb) {
> +    if (s->blk && s->bus->dma->aiocb) {
>

But s->blk mustn't be null here... IMHO we should assert() here and add a
check earlier.

Don't we already have a Launchpad bug for this BTW?

         trace_ide_cancel_dma_sync_remaining();
>          blk_drain(s->blk);
>          assert(s->bus->dma->aiocb == NULL);
> --
> 2.26.2
>
>
>

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Re: [PATCH] hw/ide: check null block pointer before blk_drain

[P J P]

[-- Attachment #1: Type: text/plain, Size: 1637 bytes --]

+-- On Mon, 31 Aug 2020, Philippe Mathieu-Daudé wrote --+
| > +++ b/hw/ide/core.c
| > @@ -718,7 +718,7 @@ void ide_cancel_dma_sync(IDEState *s)
| > -    if (s->bus->dma->aiocb) {
| > +    if (s->blk && s->bus->dma->aiocb) {
| 
| But s->blk mustn't be null here... IMHO we should assert() here and add a
| check earlier.

===
diff --git a/hw/ide/core.c b/hw/ide/core.c
index f76f7e5234..8105187f49 100644
--- a/hw/ide/core.c
+++ b/hw/ide/core.c
@@ -718,6 +718,7 @@ void ide_cancel_dma_sync(IDEState *s)
      * whole DMA operation will be submitted to disk with a single
      * aio operation with preadv/pwritev.
      */
+    assert(s->blk);
     if (s->bus->dma->aiocb) {
         trace_ide_cancel_dma_sync_remaining();
         blk_drain(s->blk);
diff --git a/hw/ide/pci.c b/hw/ide/pci.c
index b50091b615..51bb9c9abc 100644
--- a/hw/ide/pci.c
+++ b/hw/ide/pci.c
@@ -295,8 +295,11 @@ void bmdma_cmd_writeb(BMDMAState *bm, uint32_t val)
     /* Ignore writes to SSBM if it keeps the old value */
     if ((val & BM_CMD_START) != (bm->cmd & BM_CMD_START)) {
         if (!(val & BM_CMD_START)) {
-            ide_cancel_dma_sync(idebus_active_if(bm->bus));
-            bm->status &= ~BM_STATUS_DMAING;
+            IDEState *s = idebus_active_if(bm->bus);
+            if (s->blk) {
+                ide_cancel_dma_sync(s);
+                bm->status &= ~BM_STATUS_DMAING;
+            }
         } else {
             bm->cur_addr = bm->addr;
             if (!(bm->status & BM_STATUS_DMAING)) {
===


Does it look okay?

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D

Re: [PATCH] hw/ide: check null block pointer before blk_drain

[Philippe Mathieu-Daudé]

On 9/3/20 1:05 PM, P J P wrote:
> +-- On Mon, 31 Aug 2020, Philippe Mathieu-Daudé wrote --+
> | > +++ b/hw/ide/core.c
> | > @@ -718,7 +718,7 @@ void ide_cancel_dma_sync(IDEState *s)
> | > -    if (s->bus->dma->aiocb) {
> | > +    if (s->blk && s->bus->dma->aiocb) {
> | 
> | But s->blk mustn't be null here... IMHO we should assert() here and add a
> | check earlier.
> 
> ===
> diff --git a/hw/ide/core.c b/hw/ide/core.c
> index f76f7e5234..8105187f49 100644
> --- a/hw/ide/core.c
> +++ b/hw/ide/core.c
> @@ -718,6 +718,7 @@ void ide_cancel_dma_sync(IDEState *s)
>       * whole DMA operation will be submitted to disk with a single
>       * aio operation with preadv/pwritev.
>       */
> +    assert(s->blk);
>      if (s->bus->dma->aiocb) {
>          trace_ide_cancel_dma_sync_remaining();
>          blk_drain(s->blk);
> diff --git a/hw/ide/pci.c b/hw/ide/pci.c
> index b50091b615..51bb9c9abc 100644
> --- a/hw/ide/pci.c
> +++ b/hw/ide/pci.c
> @@ -295,8 +295,11 @@ void bmdma_cmd_writeb(BMDMAState *bm, uint32_t val)
>      /* Ignore writes to SSBM if it keeps the old value */
>      if ((val & BM_CMD_START) != (bm->cmd & BM_CMD_START)) {
>          if (!(val & BM_CMD_START)) {
> -            ide_cancel_dma_sync(idebus_active_if(bm->bus));
> -            bm->status &= ~BM_STATUS_DMAING;
> +            IDEState *s = idebus_active_if(bm->bus);
> +            if (s->blk) {
> +                ide_cancel_dma_sync(s);
> +                bm->status &= ~BM_STATUS_DMAING;

If you don't clear this bit the guest might keep retrying (looping).

> +            }
>          } else {
>              bm->cur_addr = bm->addr;
>              if (!(bm->status & BM_STATUS_DMAING)) {
> ===
> 
> 
> Does it look okay?
> 
> Thank you.
> --
> Prasad J Pandit / Red Hat Product Security Team
> 8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D
> 

Re: [PATCH] hw/ide: check null block pointer before blk_drain

[P J P]

[-- Attachment #1: Type: text/plain, Size: 426 bytes --]

+-- On Thu, 3 Sep 2020, Philippe Mathieu-Daudé wrote --+
| > +            if (s->blk) {
| > +                ide_cancel_dma_sync(s);
| > +                bm->status &= ~BM_STATUS_DMAING;
| 
| If you don't clear this bit the guest might keep retrying (looping).

Oh, okay will keep it out of the if(s->blk) block.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D