net: cdc_ncm: use sane defaults for rx/tx buffers

Lots of devices request much larger buffers than reasonable. This
cause real problems for users of hosts with limited resources.

Reducing the default buffer size to 16kB for such devices is
a reasonable trade-off between allowing them to aggregate traffic
and avoiding memory exhaustion on resource restrained hosts.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index f4b4398..bb53abe 100644 (file)
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -492,10 +492,18 @@ static void cdc_ncm_fix_modulus(struct usbnet *dev)
 static int cdc_ncm_setup(struct usbnet *dev)
 {
        struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
+       u32 def_rx, def_tx;
+
+       /* be conservative when selecting intial buffer size to
+        * increase the number of hosts this will work for
+        */
+       def_rx = min_t(u32, CDC_NCM_NTB_DEF_SIZE_RX,
+                      le32_to_cpu(ctx->ncm_parm.dwNtbInMaxSize));
+       def_tx = min_t(u32, CDC_NCM_NTB_DEF_SIZE_TX,
+                      le32_to_cpu(ctx->ncm_parm.dwNtbOutMaxSize));
 
        /* clamp rx_max and tx_max and inform device */
-       cdc_ncm_update_rxtx_max(dev, le32_to_cpu(ctx->ncm_parm.dwNtbInMaxSize),
-                               le32_to_cpu(ctx->ncm_parm.dwNtbOutMaxSize));
+       cdc_ncm_update_rxtx_max(dev, def_rx, def_tx);
 
        /* sanitize the modulus and remainder values */
        cdc_ncm_fix_modulus(dev);

diff --git a/include/linux/usb/cdc_ncm.h b/include/linux/usb/cdc_ncm.h
index 88d2d7f..cde5067 100644 (file)
--- a/include/linux/usb/cdc_ncm.h
+++ b/include/linux/usb/cdc_ncm.h
@@ -52,6 +52,10 @@
 #define        CDC_NCM_NTB_MAX_SIZE_TX                 32768   /* bytes */
 #define        CDC_NCM_NTB_MAX_SIZE_RX                 32768   /* bytes */
 
+/* Initial NTB length */
+#define        CDC_NCM_NTB_DEF_SIZE_TX                 16384   /* bytes */
+#define        CDC_NCM_NTB_DEF_SIZE_RX                 16384   /* bytes */
+
 /* Minimum value for MaxDatagramSize, ch. 6.2.9 */
 #define        CDC_NCM_MIN_DATAGRAM_SIZE               1514    /* bytes */