media: cx24116: prevent overflows on SNR calculus

as reported by Coverity, if reading SNR registers fail, a negative
number will be returned, causing an underflow when reading SNR
registers.

Prevent that.

Fixes: 8953db793d5b ("V4L/DVB (9178): cx24116: Add module parameter to return SNR as ESNO.")
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

diff --git a/drivers/media/dvb-frontends/cx24116.c b/drivers/media/dvb-frontends/cx24116.c
index 8b978a9f74a4e593ca6786c4d3c35a05c08291bf..f5dd3a81725a72bd0f24ec604e44905f17661f95 100644 (file)
--- a/drivers/media/dvb-frontends/cx24116.c
+++ b/drivers/media/dvb-frontends/cx24116.c
@@ -741,6 +741,7 @@ static int cx24116_read_snr_pct(struct dvb_frontend *fe, u16 *snr)
 {
        struct cx24116_state *state = fe->demodulator_priv;
        u8 snr_reading;
+       int ret;
        static const u32 snr_tab[] = { /* 10 x Table (rounded up) */
                0x00000, 0x0199A, 0x03333, 0x04ccD, 0x06667,
                0x08000, 0x0999A, 0x0b333, 0x0cccD, 0x0e667,
@@ -749,7 +750,11 @@ static int cx24116_read_snr_pct(struct dvb_frontend *fe, u16 *snr)
 
        dprintk("%s()\n", __func__);
 
-       snr_reading = cx24116_readreg(state, CX24116_REG_QUALITY0);
+       ret = cx24116_readreg(state, CX24116_REG_QUALITY0);
+       if (ret  < 0)
+               return ret;
+
+       snr_reading = ret;
 
        if (snr_reading >= 0xa0 /* 100% */)
                *snr = 0xffff;