2010-04-27 17:15:03

by Zhao, Shanyu

Subject: [PATCH 1/1] mac80211: fix rts threshold check

From: Shanyu Zhao <[email protected]>

Currently whenever rts thresold is set, every packet will use RTS
protection no matter its size exceeds the threshold or not. This is
due to a bug in the rts threshold check.
if (len > tx->local->hw.wiphy->rts_threshold) {
txrc.rts = rts = true;
}
Basically it is comparing an int (len) and a u32 (rts_threshold),
and the variable len is assigned as:
len = min_t(int, tx->skb->len + FCS_LEN,
tx->local->hw.wiphy->frag_threshold);
However, when frag_threshold is "-1", len is always "-1", which is
0xffffffff therefore rts is always set to true.

CC: [email protected]

Signed-off-by: Shanyu Zhao <[email protected]>
---
net/mac80211/tx.c | 5 +++--
1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index e2aa972..f3841f4 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -593,7 +593,8 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)
struct ieee80211_hdr *hdr = (void *)tx->skb->data;
struct ieee80211_supported_band *sband;
struct ieee80211_rate *rate;
- int i, len;
+ int i;
+ u32 len;
bool inval = false, rts = false, short_preamble = false;
struct ieee80211_tx_rate_control txrc;
u32 sta_flags;
@@ -602,7 +603,7 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)

sband = tx->local->hw.wiphy->bands[tx->channel->band];

- len = min_t(int, tx->skb->len + FCS_LEN,
+ len = min_t(u32, tx->skb->len + FCS_LEN,
tx->local->hw.wiphy->frag_threshold);

/* set up the tx rate control struct we give the RC algo */
--
1.6.0.4

2010-04-27 17:55:48

by Johannes Berg

Subject: Re: [PATCH 1/1] mac80211: fix rts threshold check

On Tue, 2010-04-27 at 11:15 -0700, [email protected] wrote:
> From: Shanyu Zhao <[email protected]>
>
> Currently whenever rts thresold is set, every packet will use RTS
> protection no matter its size exceeds the threshold or not. This is
> due to a bug in the rts threshold check.
> if (len > tx->local->hw.wiphy->rts_threshold) {
> txrc.rts = rts = true;
> }
> Basically it is comparing an int (len) and a u32 (rts_threshold),
> and the variable len is assigned as:
> len = min_t(int, tx->skb->len + FCS_LEN,
> tx->local->hw.wiphy->frag_threshold);
> However, when frag_threshold is "-1", len is always "-1", which is
> 0xffffffff therefore rts is always set to true.

D'oh. Good catch.

Reviewed-by: Johannes Berg <[email protected]>

> CC: [email protected]
>
> Signed-off-by: Shanyu Zhao <[email protected]>
> ---
> net/mac80211/tx.c | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
> index e2aa972..f3841f4 100644
> --- a/net/mac80211/tx.c
> +++ b/net/mac80211/tx.c
> @@ -593,7 +593,8 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)
> struct ieee80211_hdr *hdr = (void *)tx->skb->data;
> struct ieee80211_supported_band *sband;
> struct ieee80211_rate *rate;
> - int i, len;
> + int i;
> + u32 len;
> bool inval = false, rts = false, short_preamble = false;
> struct ieee80211_tx_rate_control txrc;
> u32 sta_flags;
> @@ -602,7 +603,7 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)
>
> sband = tx->local->hw.wiphy->bands[tx->channel->band];
>
> - len = min_t(int, tx->skb->len + FCS_LEN,
> + len = min_t(u32, tx->skb->len + FCS_LEN,
> tx->local->hw.wiphy->frag_threshold);
>
> /* set up the tx rate control struct we give the RC algo */