| Message ID | 1452254901-29796-1-git-send-email-ppandit@redhat.com |
|---|---|
| State | New |
| Headers | show |
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
+-- 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
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;