media: av7110: prevent underflow in write_ts_to_decoder()

The buf[4] value comes from the user via ts_play().  It is a value in
the u8 range.  The final length we pass to av7110_ipack_instant_repack()
is "len - (buf[4] + 1) - 4" so add a check to ensure that the length is
not negative.  It's not clear that passing a negative len value does
anything bad necessarily, but it's not best practice.

With the new bounds checking the "if (!len)" condition is no longer
possible or required so remove that.

Fixes: fd46d16d602a ("V4L/DVB (11759): dvb-ttpci: Add TS replay capability")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

diff --git a/drivers/staging/media/av7110/av7110_av.c b/drivers/staging/media/av7110/av7110_av.c
index 0bf513c26b6b5e363ea9fab610ac3b43626ab0d6..a5c5bebad306131ecf350e4f74611d28123859d3 100644 (file)
--- a/drivers/staging/media/av7110/av7110_av.c
+++ b/drivers/staging/media/av7110/av7110_av.c
@@ -823,10 +823,10 @@ static int write_ts_to_decoder(struct av7110 *av7110, int type, const u8 *buf, s
                av7110_ipack_flush(ipack);
 
        if (buf[3] & ADAPT_FIELD) {
+               if (buf[4] > len - 1 - 4)
+                       return 0;
                len -= buf[4] + 1;
                buf += buf[4] + 1;
-               if (!len)
-                       return 0;
        }
 
        av7110_ipack_instant_repack(buf + 4, len - 4, ipack);