[media] af9033: prevent unintended underflow

As spotted by Dan Carpenter <dan.carpenter@oracle.com> (thanks!), we have
improperly used an unsigned variable in a calculation that may result in a
negative number. This may cause an unintended underflow if the interface
frequency of the tuner is > approx. 40MHz.
This patch should resolve the issue, following an approach similar to what is
used in af9013.c.

[crope@iki.fi: add Reported-by]
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans-Frieder Vogt <hfvogt@gmx.net>
Reviewed-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 9 insertions, 7 deletions

diff --git a/drivers/media/dvb-frontends/af9033.c b/drivers/media/dvb-frontends/af9033.c
index 8162d939c4b2..464ad878490b 100644
--- a/drivers/media/dvb-frontends/af9033.c
+++ b/drivers/media/dvb-frontends/af9033.c
@@ -408,7 +408,7 @@ static int af9033_set_frontend(struct dvb_frontend *fe)
 {
         struct af9033_state *state = fe->demodulator_priv;
         struct dtv_frontend_properties *c = &fe->dtv_property_cache;
-        int ret, i, spec_inv;
+        int ret, i, spec_inv, sampling_freq;
         u8 tmp, buf[3], bandwidth_reg_val;
         u32 if_frequency, freq_cw, adc_freq;
 
@@ -465,18 +465,20 @@ static int af9033_set_frontend(struct dvb_frontend *fe)
                 else
                         if_frequency = 0;
 
-                while (if_frequency > (adc_freq / 2))
-                        if_frequency -= adc_freq;
+                sampling_freq = if_frequency;
 
-                if (if_frequency >= 0)
+                while (sampling_freq > (adc_freq / 2))
+                        sampling_freq -= adc_freq;
+
+                if (sampling_freq >= 0)
                         spec_inv *= -1;
                 else
-                        if_frequency *= -1;
+                        sampling_freq *= -1;
 
-                freq_cw = af9033_div(state, if_frequency, adc_freq, 23ul);
+                freq_cw = af9033_div(state, sampling_freq, adc_freq, 23ul);
 
                 if (spec_inv == -1)
-                        freq_cw *= -1;
+                        freq_cw = 0x800000 - freq_cw;
 
                 /* get adc multiplies */
                 ret = af9033_rd_reg(state, 0x800045, &tmp);