[PATCH] drivers/staging/iio/frequency/ad9832.c: fix division by zero in ad9832_calc_freqreg()

[Zicheng Qu]

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@xxxxxxxxxxxxxxx>
Signed-off-by: Zicheng Qu <quzicheng@xxxxxxxxxx>
---
 drivers/staging/iio/frequency/ad9832.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/iio/frequency/ad9832.c b/drivers/staging/iio/frequency/ad9832.c
index 6c390c4eb26d..492612e8f8ba 100644
--- 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) |
-- 
2.34.1