* [Qemu-devel] [PATCH] ide: ahci: reset ncq object to unused on error
@ 2016-01-08 12:08 P J P
2016-01-08 18:39 ` John Snow
0 siblings, 1 reply; 3+ messages in thread
From: P J P @ 2016-01-08 12:08 UTC (permalink / raw
To: qemu-block; +Cc: Qinghao Tang, John Snow, qemu-devel, Prasad J Pandit
From: Prasad J Pandit <pjp@fedoraproject.org>
When processing NCQ commands, ACHI device emulation prepares a
NCQ transfer object; To which an aio control block(aiocb) object
is assigned in 'execute_ncq_command'. In case, when the NCQ
command is invalid, the 'aiocb' object is not assigned, and NCQ
transfer object is left as 'used'. This leads to a use after
free error in 'bdrv_aio_cancel_async' via 'ahci_reset_port'.
Reset NCQ transfer object to 'unused' to avoid it.
Reported-by: Qinghao Tang <luodalongde@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
hw/ide/ahci.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
index dd1912e..e359127 100644
--- a/hw/ide/ahci.c
+++ b/hw/ide/ahci.c
@@ -1014,6 +1014,7 @@ static void execute_ncq_command(NCQTransferState *ncq_tfs)
DPRINTF(port, "error: unsupported NCQ command (0x%02x) received\n",
ncq_tfs->cmd);
qemu_sglist_destroy(&ncq_tfs->sglist);
+ ncq_tfs->used = 0;
ncq_err(ncq_tfs);
}
}
@@ -1081,6 +1082,7 @@ static void process_ncq_command(AHCIState *s, int port, uint8_t *cmd_fis,
"is smaller than the requested size (0x%zx)",
ncq_tfs->sglist.size, size);
qemu_sglist_destroy(&ncq_tfs->sglist);
+ ncq_tfs->used = 0;
ncq_err(ncq_tfs);
ahci_trigger_irq(ad->hba, ad, PORT_IRQ_OVERFLOW);
return;
--
2.4.3
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] ide: ahci: reset ncq object to unused on error
2016-01-08 12:08 [Qemu-devel] [PATCH] ide: ahci: reset ncq object to unused on error P J P
@ 2016-01-08 18:39 ` John Snow
2016-01-08 19:16 ` P J P
0 siblings, 1 reply; 3+ messages in thread
From: John Snow @ 2016-01-08 18:39 UTC (permalink / raw
To: P J P, qemu-block; +Cc: Qinghao Tang, qemu-devel, Prasad J Pandit
On 01/08/2016 07:08 AM, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> When processing NCQ commands, ACHI device emulation prepares a
> NCQ transfer object; To which an aio control block(aiocb) object
> is assigned in 'execute_ncq_command'. In case, when the NCQ
> command is invalid, the 'aiocb' object is not assigned, and NCQ
> transfer object is left as 'used'. This leads to a use after
> free error in 'bdrv_aio_cancel_async' via 'ahci_reset_port'.
> Reset NCQ transfer object to 'unused' to avoid it.
>
The commit message is a little misleading:
In both of these error pathways, AIOCB is actually never assigned to
begin with. However, neglecting to set used = 0 will indeed cause
ahci_reset_port to try to read these values.
So it's not necessarily a use-after-free.
Regardless, good find!
> Reported-by: Qinghao Tang <luodalongde@gmail.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
> hw/ide/ahci.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> index dd1912e..e359127 100644
> --- a/hw/ide/ahci.c
> +++ b/hw/ide/ahci.c
> @@ -1014,6 +1014,7 @@ static void execute_ncq_command(NCQTransferState *ncq_tfs)
> DPRINTF(port, "error: unsupported NCQ command (0x%02x) received\n",
> ncq_tfs->cmd);
> qemu_sglist_destroy(&ncq_tfs->sglist);
> + ncq_tfs->used = 0;
> ncq_err(ncq_tfs);
> }
> }
> @@ -1081,6 +1082,7 @@ static void process_ncq_command(AHCIState *s, int port, uint8_t *cmd_fis,
> "is smaller than the requested size (0x%zx)",
> ncq_tfs->sglist.size, size);
> qemu_sglist_destroy(&ncq_tfs->sglist);
> + ncq_tfs->used = 0;
> ncq_err(ncq_tfs);
> ahci_trigger_irq(ad->hba, ad, PORT_IRQ_OVERFLOW);
> return;
>
I think it should be safe to put ncq_tfs->used = 0 directly inside of
ncq_err, and that way we won't have any other error pathways omitting
this in the future.
--js
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] ide: ahci: reset ncq object to unused on error
2016-01-08 18:39 ` John Snow
@ 2016-01-08 19:16 ` P J P
0 siblings, 0 replies; 3+ messages in thread
From: P J P @ 2016-01-08 19:16 UTC (permalink / raw
To: John Snow; +Cc: Qinghao Tang, qemu-devel, qemu-block
+-- On Fri, 8 Jan 2016, John Snow wrote --+
| In both of these error pathways, AIOCB is actually never assigned to
| begin with.
True, it's mentioned in the commit message.
| So it's not necessarily a use-after-free.
Yes, right.
| I think it should be safe to put ncq_tfs->used = 0 directly inside of
| ncq_err, and that way we won't have any other error pathways omitting
| this in the future.
Okay, I'll send an updated patch.
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] 3+ messages in thread
end of thread, other threads:[~2016-01-08 19:17 UTC | newest]
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2016-01-08 12:08 [Qemu-devel] [PATCH] ide: ahci: reset ncq object to unused on error P J P
2016-01-08 18:39 ` John Snow
2016-01-08 19:16 ` P J P
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