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

commit 451a2886b6bf90e2fb378f7c46c655450fb96e81 upstream.

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)
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[lizf: Backported to 3.4: s/MAX_UIOVEC/UIO_MAXIOV]
Signed-off-by: Zefan Li <lizefan@huawei.com>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index fb119ce06ae57865348cdfbbdda8e2bc00e727a7..ebe83f7f63e7bf4e91abc957eafa94b7c7fa47f4 100644 (file)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1687,6 +1687,9 @@ static int sg_start_req(Sg_request *srp, unsigned char *cmd)
                        md->from_user = 0;
        }
 
+       if (unlikely(iov_count > UIO_MAXIOV))
+               return -EINVAL;
+
        if (iov_count) {
                int len, size = sizeof(struct sg_iovec) * iov_count;
                struct iovec *iov;