[SCSI] erase invalid data returned by device

This patch (as1108) fixes a problem that can occur with certain USB
mass-storage devices: They return invalid data together with a residue
indicating that the data should be ignored.  Rather than leave the
invalid data in a transfer buffer, where it can get misinterpreted,
the patch clears the invalid portion of the buffer.

This solves a problem (wrong write-protect setting detected) reported
by Maciej Rutecki and Peter Teoh.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Peter Teoh <htmldeveloper@gmail.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index a82d2fe80fb5..cbf55d59a54c 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -207,6 +207,15 @@ int scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
          */
         blk_execute_rq(req->q, NULL, req, 1);
 
+        /*
+         * Some devices (USB mass-storage in particular) may transfer
+         * garbage data together with a residue indicating that the data
+         * is invalid.  Prevent the garbage from being misinterpreted
+         * and prevent security leaks by zeroing out the excess data.
+         */
+        if (unlikely(req->data_len > 0 && req->data_len <= bufflen))
+                memset(buffer + (bufflen - req->data_len), 0, req->data_len);
+
         ret = req->errors;
  out:
         blk_put_request(req);