In the rtw_pci_init_rx_ring function the "if (len > TRX_BD_IDX_MASK)"
statement guarantees that len is less than or equal to GENMASK(11, 0) or
in other words that len is less than or equal to 4095. However the
rx_ring->buf has a size of RTK_MAX_RX_DESC_NUM (defined as 512). This
way it is possible an out-of-bounds write in the for statement due to
the i variable can exceed the rx_ring->buff size.
However, this overflow never happens due to the rtw_pci_init_rx_ring is
only ever called with a fixed constant of RTK_MAX_RX_DESC_NUM. But it is
better to be defensive in this case and add a new check to avoid
overflows if this function is called in a future with a value greater
than 512.
Cc: [email protected]
Addresses-Coverity-ID: 1461515 ("Out-of-bounds write")
Fixes: e3037485c68ec ("rtw88: new Realtek 802.11ac driver")
Signed-off-by: Len Baker <[email protected]>
---
Changelog v1 -> v2
- Remove the macro ARRAY_SIZE from the for loop (Pkshih, Brian Norris).
- Add a new check for the len variable (Pkshih, Brian Norris).
drivers/net/wireless/realtek/rtw88/pci.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/net/wireless/realtek/rtw88/pci.c b/drivers/net/wireless/realtek/rtw88/pci.c
index e7d17ab8f113..53dc90276693 100644
--- a/drivers/net/wireless/realtek/rtw88/pci.c
+++ b/drivers/net/wireless/realtek/rtw88/pci.c
@@ -273,6 +273,11 @@ static int rtw_pci_init_rx_ring(struct rtw_dev *rtwdev,
return -EINVAL;
}
+ if (len > ARRAY_SIZE(rx_ring->buf)) {
+ rtw_err(rtwdev, "len %d exceeds maximum RX ring buffer\n", len);
+ return -EINVAL;
+ }
+
head = dma_alloc_coherent(&pdev->dev, ring_sz, &dma, GFP_KERNEL);
if (!head) {
rtw_err(rtwdev, "failed to allocate rx ring\n");
--
2.25.1
On Fri, Jul 16, 2021 at 05:53:11PM +0200, Len Baker wrote:
> In the rtw_pci_init_rx_ring function the "if (len > TRX_BD_IDX_MASK)"
> statement guarantees that len is less than or equal to GENMASK(11, 0) or
> in other words that len is less than or equal to 4095. However the
> rx_ring->buf has a size of RTK_MAX_RX_DESC_NUM (defined as 512). This
> way it is possible an out-of-bounds write in the for statement due to
> the i variable can exceed the rx_ring->buff size.
>
> However, this overflow never happens due to the rtw_pci_init_rx_ring is
> only ever called with a fixed constant of RTK_MAX_RX_DESC_NUM. But it is
> better to be defensive in this case and add a new check to avoid
> overflows if this function is called in a future with a value greater
> than 512.
If this can never happen, then no, this is not needed. Why would you
check twice for the same thing?
thanks,
greg k-h
On Sat, Jul 17, 2021 at 03:33:43PM +0200, Len Baker wrote:
> On Fri, Jul 16, 2021 at 07:20:48PM +0200, Greg KH wrote:
> > On Fri, Jul 16, 2021 at 05:53:11PM +0200, Len Baker wrote:
> > > In the rtw_pci_init_rx_ring function the "if (len > TRX_BD_IDX_MASK)"
> > > statement guarantees that len is less than or equal to GENMASK(11, 0) or
> > > in other words that len is less than or equal to 4095. However the
> > > rx_ring->buf has a size of RTK_MAX_RX_DESC_NUM (defined as 512). This
> > > way it is possible an out-of-bounds write in the for statement due to
> > > the i variable can exceed the rx_ring->buff size.
> > >
> > > However, this overflow never happens due to the rtw_pci_init_rx_ring is
> > > only ever called with a fixed constant of RTK_MAX_RX_DESC_NUM. But it is
> > > better to be defensive in this case and add a new check to avoid
> > > overflows if this function is called in a future with a value greater
> > > than 512.
> >
> > If this can never happen, then no, this is not needed.
>
> Then, if this can never happen, the current check would not be necessary
> either.
>
> > Why would you check twice for the same thing?
>
> Ok, it makes no sense to double check the "len" variable twice. So, I
> propose to modify the current check as follows:
>
> diff --git a/drivers/net/wireless/realtek/rtw88/pci.c b/drivers/net/wireless/realtek/rtw88/pci.c
> index e7d17ab8f113..0fd140523868 100644
> --- a/drivers/net/wireless/realtek/rtw88/pci.c
> +++ b/drivers/net/wireless/realtek/rtw88/pci.c
> @@ -268,8 +268,8 @@ static int rtw_pci_init_rx_ring(struct rtw_dev *rtwdev,
> int i, allocated;
> int ret = 0;
>
> - if (len > TRX_BD_IDX_MASK) {
> - rtw_err(rtwdev, "len %d exceeds maximum RX entries\n", len);
> + if (len > ARRAY_SIZE(rx_ring->buf)) {
> + rtw_err(rtwdev, "len %d exceeds maximum RX ring buffer\n", len);
> return -EINVAL;
> }
>
> This way the overflow can never happen with the current call to
> rtw_pci_init_rx_ring function or with a future call with a "len" parameter
> greater than 512. What do you think?
>
> If there are no objections I will send a v3 for review.
>
> Another question: If this can never happen should I include the "Fixes" tag,
> "Addresses-Coverity-ID" tag and Cc to stable?
If it can never happen, why have this check at all?
Looks like a Coverity false positive?
thanks,
greg k-h
On Sat, Jul 17, 2021 at 07:33:49PM +0200, Greg KH wrote:
> On Sat, Jul 17, 2021 at 03:33:43PM +0200, Len Baker wrote:
> > Another question: If this can never happen should I include the "Fixes" tag,
> > "Addresses-Coverity-ID" tag and Cc to stable?
>
> If it can never happen, why have this check at all?
>
> Looks like a Coverity false positive?
Ok, then I will remove the check and I will send a patch for review.
>
> thanks,
>
> greg k-h
Regards,
Len