USB: make the usbfs memory limit configurable

The 16-MB global limit on memory used by usbfs isn't suitable for all
people.  It's a reasonable default, but there are applications
(especially for SuperSpeed devices) that need a lot more.

This patch (as1498) creates a writable module parameter for usbcore to
control the global limit.  The default is still 16 MB, but users can
change it at runtime, even after usbcore has been loaded.  As a
special case, setting the value to 0 is treated the same as the hard
limit of 2047 MB.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 22 insertions, 4 deletions

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index b69768b7d226..d8cf06f186f2 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -110,15 +110,33 @@ enum snoop_when {
 #define USB_DEVICE_DEV          MKDEV(USB_DEVICE_MAJOR, 0)
 
 /* Limit on the total amount of memory we can allocate for transfers */
-#define MAX_USBFS_MEMORY_USAGE  16777216        /* 16 MB */
+static unsigned usbfs_memory_mb = 16;
+module_param(usbfs_memory_mb, uint, 0644);
+MODULE_PARM_DESC(usbfs_memory_mb,
+                "maximum MB allowed for usbfs buffers (0 = no limit)");
+
+/* Hard limit, necessary to avoid aithmetic overflow */
+#define USBFS_XFER_MAX          (UINT_MAX / 2 - 1000000)
 
 static atomic_t usbfs_memory_usage;     /* Total memory currently allocated */
 
 /* Check whether it's okay to allocate more memory for a transfer */
 static int usbfs_increase_memory_usage(unsigned amount)
 {
+        unsigned lim;
+
+        /*
+         * Convert usbfs_memory_mb to bytes, avoiding overflows.
+         * 0 means use the hard limit (effectively unlimited).
+         */
+        lim = ACCESS_ONCE(usbfs_memory_mb);
+        if (lim == 0 || lim > (USBFS_XFER_MAX >> 20))
+                lim = USBFS_XFER_MAX;
+        else
+                lim <<= 20;
+
         atomic_add(amount, &usbfs_memory_usage);
-        if (atomic_read(&usbfs_memory_usage) <= MAX_USBFS_MEMORY_USAGE)
+        if (atomic_read(&usbfs_memory_usage) <= lim)
                 return 0;
         atomic_sub(amount, &usbfs_memory_usage);
         return -ENOMEM;
@@ -907,7 +925,7 @@ static int proc_bulk(struct dev_state *ps, void __user *arg)
         if (!usb_maxpacket(dev, pipe, !(bulk.ep & USB_DIR_IN)))
                 return -EINVAL;
         len1 = bulk.len;
-        if (len1 > MAX_USBFS_MEMORY_USAGE)
+        if (len1 >= USBFS_XFER_MAX)
                 return -EINVAL;
         ret = usbfs_increase_memory_usage(len1 + sizeof(struct urb));
         if (ret)
@@ -1227,7 +1245,7 @@ static int proc_do_submiturb(struct dev_state *ps, struct usbdevfs_urb *uurb,
                 return -EINVAL;
         }
 
-        if (uurb->buffer_length > MAX_USBFS_MEMORY_USAGE) {
+        if (uurb->buffer_length >= USBFS_XFER_MAX) {
                 ret = -EINVAL;
                 goto error;
         }