sg_start_req(): make sure that there's not too many elements in iovec

unfortunately, allowing an arbitrary 16bit value means a possibility of
overflow in the calculation of total number of pages in bio_map_user_iov() -
we rely on there being no more than PAGE_SIZE members of sum in the
first loop there.  If that sum wraps around, we end up allocating
too small array of pointers to pages and it's easy to overflow it in
the second loop.

X-Coverup: TINC (and there's no lumber cartel either)
Cc: stable@vger.kernel.org # way, way back
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index d383f84869aa45475bb25f149123092a0f3beb0c..b5a4db8832236053fd0b516bf8b42eb1493f002b 100644 (file)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1744,6 +1744,9 @@ sg_start_req(Sg_request *srp, unsigned char *cmd)
                        md->from_user = 0;
        }
 
+       if (unlikely(iov_count > MAX_UIOVEC))
+               return -EINVAL;
+
        if (iov_count) {
                int size = sizeof(struct iovec) * iov_count;
                struct iovec *iov;