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Re: [Qemu-devel] [PATCH] ide: ahci: reset ncq object to unused on error
From: |
John Snow |
Subject: |
Re: [Qemu-devel] [PATCH] ide: ahci: reset ncq object to unused on error |
Date: |
Fri, 8 Jan 2016 13:39:28 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 01/08/2016 07:08 AM, P J P wrote:
> From: Prasad J Pandit <address@hidden>
>
> 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 <address@hidden>
> Signed-off-by: Prasad J Pandit <address@hidden>
> ---
> 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