[PATCH v3] hdlcdrv: Fix divide by zero in hdlcdrv_ioctl

[Firo Yang]

syszkaller fuzzer triggered a divide by zero, when set calibration
through ioctl().

To fix it, test 'bitrate' if it is negative or 0, just return -EINVAL.

Reported-by: Andrey Konovalov <andreyk...@google.com>
Signed-off-by: Firo Yang <fir...@gmail.com>
---
v2->v3:
        Just fix divide error and remove netif_running() test.
        Refine the testing code as David Miller suggested.

v1->v2:
        Change Reported-by to Andrey Konovalov.
        Send it to original report thread.

v0->v1:
        Reviewed by walter harms <wha...@bfs.de>.
        Return ENODEV instead of EPERM if !netif_running(dev)
        Check if s->par.bitrate > 0.
 drivers/net/hamradio/hdlcdrv.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/hamradio/hdlcdrv.c b/drivers/net/hamradio/hdlcdrv.c
index 8c3633c..97e3bc6 100644
--- a/drivers/net/hamradio/hdlcdrv.c
+++ b/drivers/net/hamradio/hdlcdrv.c
@@ -576,6 +576,8 @@ static int hdlcdrv_ioctl(struct net_device *dev, struct 
ifreq *ifr, int cmd)
        case HDLCDRVCTL_CALIBRATE:
                if(!capable(CAP_SYS_RAWIO))
                        return -EPERM;
+               if (s->par.bitrate <= 0)
+                       return -EINVAL;
                if (bi.data.calibrate > INT_MAX / s->par.bitrate)
                        return -EINVAL;
                s->hdlctx.calibrate = bi.data.calibrate * s->par.bitrate / 16;
-- 
2.9.4