[patch 26/76] usb-storage: dont access beyond the end of the sg buffer

[Chris Wright]

-stable review patch.  If anyone has any objections, please let us know.
---------------------

From: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>

This patch (as1038) fixes a bug in usb_stor_access_xfer_buf() and
usb_stor_set_xfer_buf() (the bug was originally found by Boaz
Harrosh): The routine must not attempt to write beyond the end of a
scatter-gather list or beyond the number of bytes requested.

This is the minimal 2.6.24 equivalent to as1035 +
as1037 (7084191d53b224b953c8e1db525ea6c31aca5fc7 "USB:
usb-storage: don't access beyond the end of the sg buffer" +
6d512a80c26d87f8599057c86dc920fbfe0aa3aa "usb-storage: update earlier
scatter-gather bug fix").  Mark Glines has confirmed that it fixes
his problem.

Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Mark Glines <mark@xxxxxxxxxx>
Cc: Boaz Harrosh <bharrosh@xxxxxxxxxxx>
Signed-off-by: Chris Wright <chrisw@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 drivers/usb/storage/protocol.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/usb/storage/protocol.c
+++ b/drivers/usb/storage/protocol.c
@@ -194,7 +194,7 @@ unsigned int usb_stor_access_xfer_buf(un
 		 * and the starting offset within the page, and update
 		 * the *offset and *index values for the next loop. */
 		cnt = 0;
-		while (cnt < buflen) {
+		while (cnt < buflen && sg) {
 			struct page *page = sg_page(sg) +
 					((sg->offset + *offset) >> PAGE_SHIFT);
 			unsigned int poff =
@@ -249,7 +249,8 @@ void usb_stor_set_xfer_buf(unsigned char
 	unsigned int offset = 0;
 	struct scatterlist *sg = NULL;
 
-	usb_stor_access_xfer_buf(buffer, buflen, srb, &sg, &offset,
+	buflen = min(buflen, srb->request_bufflen);
+	buflen = usb_stor_access_xfer_buf(buffer, buflen, srb, &sg, &offset,
 			TO_XFER_BUF);
 	if (buflen < srb->request_bufflen)
 		srb->resid = srb->request_bufflen - buflen;

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