staging: iio: frequency: ad9832: fix division by zero in ad9832_calc_freqreg()

In the ad9832_write_frequency() function, clk_get_rate() might return 0.
This can lead to a division by zero when calling ad9832_calc_freqreg().
The check if (fout > (clk_get_rate(st->mclk) / 2)) does not protect
against the case when fout is 0. The ad9832_write_frequency() function
is called from ad9832_write(), and fout is derived from a text buffer,
which can contain any value.

Link: https://lore.kernel.org/all/2024100904-CVE-2024-47663-9bdc@gregkh/
Fixes: ea707584bac1 ("Staging: IIO: DDS: AD9832 / AD9835 driver")
Cc: stable@vger.kernel.org
Signed-off-by: Zicheng Qu <quzicheng@huawei.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/20241022134354.574614-1-quzicheng@huawei.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c
index 6c390c4eb26deaa5c716facf3e69e51436545067..492612e8f8bad5bbbda14daec6a558934323518d 100644 (file)
--- a/drivers/staging/iio/frequency/ad9832.c
+++ b/drivers/staging/iio/frequency/ad9832.c
@@ -129,12 +129,15 @@ static unsigned long ad9832_calc_freqreg(unsigned long mclk, unsigned long fout)
 static int ad9832_write_frequency(struct ad9832_state *st,
                                  unsigned int addr, unsigned long fout)
 {
+       unsigned long clk_freq;
        unsigned long regval;
 
-       if (fout > (clk_get_rate(st->mclk) / 2))
+       clk_freq = clk_get_rate(st->mclk);
+
+       if (!clk_freq || fout > (clk_freq / 2))
                return -EINVAL;
 
-       regval = ad9832_calc_freqreg(clk_get_rate(st->mclk), fout);
+       regval = ad9832_calc_freqreg(clk_freq, fout);
 
        st->freq_data[0] = cpu_to_be16((AD9832_CMD_FRE8BITSW << CMD_SHIFT) |
                                        (addr << ADD_SHIFT) |