2019-10-20 01:14:53

by Larry Finger

Subject: [PATCH V2] rtlwifi: rtl_pci: Fix problem of too small skb->len

In commit 8020919a9b99 ("mac80211: Properly handle SKB with radiotap
only"), buffers whose length is too short cause a WARN_ON(1) to be
executed. This change exposed a fault in rtlwifi drivers, which is fixed
by increasing the length of the affected buffer before it is sent to
mac80211.

Cc: Stable <[email protected]> # v5.0+
Signed-off-by: Larry Finger <[email protected]>
---
V2 - added missing usage of new len
---
Please Apply to 5.4
---
drivers/net/wireless/realtek/rtlwifi/pci.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/realtek/rtlwifi/pci.c b/drivers/net/wireless/realtek/rtlwifi/pci.c
index 6087ec7a90a6..3e9185162e51 100644
--- a/drivers/net/wireless/realtek/rtlwifi/pci.c
+++ b/drivers/net/wireless/realtek/rtlwifi/pci.c
@@ -692,12 +692,15 @@ static void _rtl_pci_rx_to_mac80211(struct ieee80211_hw *hw,
dev_kfree_skb_any(skb);
} else {
struct sk_buff *uskb = NULL;
+ int len = skb->len;

+ if (unlikely(len <= FCS_LEN))
+ len = FCS_LEN + 2;
uskb = dev_alloc_skb(skb->len + 128);
if (likely(uskb)) {
memcpy(IEEE80211_SKB_RXCB(uskb), &rx_status,
sizeof(rx_status));
- skb_put_data(uskb, skb->data, skb->len);
+ skb_put_data(uskb, skb->data, len);
dev_kfree_skb_any(skb);
ieee80211_rx_irqsafe(hw, uskb);
} else {
--
2.23.0

2019-10-20 08:32:43

by Kalle Valo

Subject: Re: [PATCH V2] rtlwifi: rtl_pci: Fix problem of too small skb->len

Larry Finger <[email protected]> writes:

> In commit 8020919a9b99 ("mac80211: Properly handle SKB with radiotap
> only"), buffers whose length is too short cause a WARN_ON(1) to be
> executed. This change exposed a fault in rtlwifi drivers, which is fixed
> by increasing the length of the affected buffer before it is sent to
> mac80211.

With what frames, or in what scenarios, do you get these warnings?

> Cc: Stable <[email protected]> # v5.0+
> Signed-off-by: Larry Finger <[email protected]>
> ---
> V2 - added missing usage of new len
> ---
> Please Apply to 5.4
> ---
> drivers/net/wireless/realtek/rtlwifi/pci.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/realtek/rtlwifi/pci.c b/drivers/net/wireless/realtek/rtlwifi/pci.c
> index 6087ec7a90a6..3e9185162e51 100644
> --- a/drivers/net/wireless/realtek/rtlwifi/pci.c
> +++ b/drivers/net/wireless/realtek/rtlwifi/pci.c
> @@ -692,12 +692,15 @@ static void _rtl_pci_rx_to_mac80211(struct ieee80211_hw *hw,
> dev_kfree_skb_any(skb);
> } else {
> struct sk_buff *uskb = NULL;
> + int len = skb->len;
>
> + if (unlikely(len <= FCS_LEN))
> + len = FCS_LEN + 2;

I don't understand this change, I think this needs a comment in the
code, or better yet a proper define documenting the meaning of the
value. What does these two bytes contain? Or are you just working around
the mac80211 warning by increasing the length with a random value you
chose?

--
Kalle Valo

2019-10-20 20:14:10

by Larry Finger

Subject: Re: [PATCH V2] rtlwifi: rtl_pci: Fix problem of too small skb->len

On 10/20/19 3:28 AM, Kalle Valo wrote:
> Larry Finger <[email protected]> writes:
>
>> In commit 8020919a9b99 ("mac80211: Properly handle SKB with radiotap
>> only"), buffers whose length is too short cause a WARN_ON(1) to be
>> executed. This change exposed a fault in rtlwifi drivers, which is fixed
>> by increasing the length of the affected buffer before it is sent to
>> mac80211.
>
> With what frames, or in what scenarios, do you get these warnings?

I am not sure how they happen, but the firmware reports a 3-byte packet, which
leads to the warning. After looking at the code path again, a better approach
would be to consider those short packets the same way that those with CRC or
hardware errors and drop them.

After more testing, I will send V3 using that approach.

Larry