Return-path: Received: from mail-ie0-f173.google.com ([209.85.223.173]:45970 "EHLO mail-ie0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751056AbaJADpK (ORCPT ); Tue, 30 Sep 2014 23:45:10 -0400 Received: by mail-ie0-f173.google.com with SMTP id tp5so259147ieb.4 for ; Tue, 30 Sep 2014 20:45:09 -0700 (PDT) From: Mark Asselstine To: helmut.schaa@googlemail.com, sgruszka@redhat.com Cc: users@rt2x00.serialmonkey.com, linux-wireless@vger.kernel.org Subject: [PATCH] rt2x00: rt2x00queue: avoid using more headroom then driver requested Date: Tue, 30 Sep 2014 23:45:57 -0400 Message-Id: <1412135157-13520-1-git-send-email-asselsm@gmail.com> (sfid-20141001_054524_238940_CDF0DEEC) Sender: linux-wireless-owner@vger.kernel.org List-ID: 'struct ieee80211_hw' contains 'extra_tx_headroom' which it defines as "headroom to reserve in each transmit skb for use by the driver". This value is properly setup during rt2x00lib_probe_hw() to account for all the rt2x00lib's purposes, including DMA alignment and L2 pad if needed. As such under all circumstances the proper amount of headroom is allocated to a skb such that under any usage we would not ever use more headroom then is allotted. However rt2x00queue_write_tx_frame() uses up the headroom (via calls to skb_push) allotted for L2 padding (with a potential call to rt2x00queue_insert_l2pad()) and uses up the headroom allotted to DMA alignment (with a potential call to rt2x00queue_align_frame()) and then proceeds to use up 'extra_tx_headroom' (in a call to rt2x00queue_write_tx_data()) So the driver has requested just 'extra_tx_headroom' worth of headroom and we have used up 'extra_tx_headroom' + DMA + L2PAD worth. As such it is possible to hit a 'skb_under_panic', where we have used up all the available headroom. Since extra_tx_headroom was calculated as a function of winfo_size, desc_size, RT2X00_L2PAD_SIZE and RT2X00_ALIGN_SIZE we can simply remove the part for alignment and padding and we will know how much is left to use up (for txdesc) and only use that much. Keeping the driver's use of headroom to what it requested via extra_tx_headroom. Signed-off-by: Mark Asselstine --- drivers/net/wireless/rt2x00/rt2x00queue.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/net/wireless/rt2x00/rt2x00queue.c b/drivers/net/wireless/rt2x00/rt2x00queue.c index 8e68f87..2a48bf5 100644 --- a/drivers/net/wireless/rt2x00/rt2x00queue.c +++ b/drivers/net/wireless/rt2x00/rt2x00queue.c @@ -522,6 +522,7 @@ static int rt2x00queue_write_tx_data(struct queue_entry *entry, struct txentry_desc *txdesc) { struct rt2x00_dev *rt2x00dev = entry->queue->rt2x00dev; + unsigned int avail_extra_tx_headroom = rt2x00dev->extra_tx_headroom; /* * This should not happen, we already checked the entry @@ -538,10 +539,18 @@ static int rt2x00queue_write_tx_data(struct queue_entry *entry, } /* - * Add the requested extra tx headroom in front of the skb. + * Add room for data at the front of the buffer for txdesc. The space + * needed for this was accounted for in extra_tx_headroom, we just + * need to remove the amount allocated for padding and alignment + * to get what is left for txdesc. */ - skb_push(entry->skb, rt2x00dev->extra_tx_headroom); - memset(entry->skb->data, 0, rt2x00dev->extra_tx_headroom); + if (test_bit(REQUIRE_L2PAD, &rt2x00dev->cap_flags)) + avail_extra_tx_headroom -= RT2X00_L2PAD_SIZE; + else if (test_bit(REQUIRE_DMA, &rt2x00dev->cap_flags)) + avail_extra_tx_headroom -= RT2X00_ALIGN_SIZE; + + skb_push(entry->skb, avail_extra_tx_headroom); + memset(entry->skb->data, 0, avail_extra_tx_headroom); /* * Call the driver's write_tx_data function, if it exists. -- 1.9.1