rt2x00: Fix double usage of skb->cb in USB RX path.

It is not safe to use the skb->cb area for both the rxd and
skb_frame_desc data at the same time, while they occupy an overlapping
piece of memory. This can lead to hard to trace crashes as pointers
within skb_frame_desc are pointing into nowhere, or the rxd data is
overwritten with non-sense.

Fix it by copying the rxd to a small buffer on the stack.

Signed-off-by: Gertjan van Wingerde <gwingerde@kpnplanet.nl>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

3 files changed, 9 insertions, 19 deletions

diff --git a/drivers/net/wireless/rt2x00/rt2500usb.c b/drivers/net/wireless/rt2x00/rt2500usb.c
index 1bfb68a920a8..9851cefaabf3 100644
--- a/drivers/net/wireless/rt2x00/rt2500usb.c
+++ b/drivers/net/wireless/rt2x00/rt2500usb.c
@@ -1156,14 +1156,10 @@ static void rt2500usb_fill_rxdone(struct queue_entry *entry,
         u32 word1;
 
         /*
-         * Copy descriptor to the skb->cb array, this has 2 benefits:
-         * 1) Each descriptor word is 4 byte aligned.
-         * 2) Descriptor is safe  from moving of frame data in rt2x00usb.
+         * Copy descriptor to the skbdesc->desc buffer, making it safe from moving of
+         * frame data in rt2x00usb.
          */
-        skbdesc->desc_len =
-            min_t(u16, entry->queue->desc_size, sizeof(entry->skb->cb));
-        memcpy(entry->skb->cb, rxd, skbdesc->desc_len);
-        skbdesc->desc = entry->skb->cb;
+        memcpy(skbdesc->desc, rxd, skbdesc->desc_len);
         rxd = (__le32 *)skbdesc->desc;
 
         /*
diff --git a/drivers/net/wireless/rt2x00/rt2x00usb.c b/drivers/net/wireless/rt2x00/rt2x00usb.c
index 33833bc6d665..68d87f09e054 100644
--- a/drivers/net/wireless/rt2x00/rt2x00usb.c
+++ b/drivers/net/wireless/rt2x00/rt2x00usb.c
@@ -267,6 +267,7 @@ static void rt2x00usb_interrupt_rxdone(struct urb *urb)
         struct sk_buff *skb;
         struct skb_frame_desc *skbdesc;
         struct rxdone_entry_desc rxdesc;
+        u8 rxd[32];
 
         if (!test_bit(DEVICE_ENABLED_RADIO, &rt2x00dev->flags) ||
             !test_and_clear_bit(ENTRY_OWNER_DEVICE_DATA, &entry->flags))
@@ -286,16 +287,13 @@ static void rt2x00usb_interrupt_rxdone(struct urb *urb)
         skbdesc = get_skb_frame_desc(entry->skb);
         memset(skbdesc, 0, sizeof(*skbdesc));
         skbdesc->entry = entry;
+        skbdesc->desc = rxd;
+        skbdesc->desc_len = entry->queue->desc_size;
 
         memset(&rxdesc, 0, sizeof(rxdesc));
         rt2x00dev->ops->lib->fill_rxdone(entry, &rxdesc);
 
         /*
-         * Trim the skb to the correct size.
-         */
-        skb_trim(entry->skb, rxdesc.size);
-
-        /*
          * Allocate a new sk buffer to replace the current one.
          * If allocation fails, we should drop the current frame
          * so we can recycle the existing sk buffer for the new frame.
diff --git a/drivers/net/wireless/rt2x00/rt73usb.c b/drivers/net/wireless/rt2x00/rt73usb.c
index 800a1e278d1e..505a9f5e09e9 100644
--- a/drivers/net/wireless/rt2x00/rt73usb.c
+++ b/drivers/net/wireless/rt2x00/rt73usb.c
@@ -1428,14 +1428,10 @@ static void rt73usb_fill_rxdone(struct queue_entry *entry,
         u32 word1;
 
         /*
-         * Copy descriptor to the skb->cb array, this has 2 benefits:
-         * 1) Each descriptor word is 4 byte aligned.
-         * 2) Descriptor is safe  from moving of frame data in rt2x00usb.
+         * Copy descriptor to the skbdesc->desc buffer, making it safe from moving of
+         * frame data in rt2x00usb.
          */
-        skbdesc->desc_len =
-            min_t(u16, entry->queue->desc_size, sizeof(entry->skb->cb));
-        memcpy(entry->skb->cb, rxd, skbdesc->desc_len);
-        skbdesc->desc = entry->skb->cb;
+        memcpy(skbdesc->desc, rxd, skbdesc->desc_len);
         rxd = (__le32 *)skbdesc->desc;
 
         /*