In xc4000_get_frequency():
*freq = priv->freq_hz + priv->freq_offset;
The code accesses priv->freq_hz and priv->freq_offset without holding any
lock.
In xc4000_set_params():
// Code that updates priv->freq_hz and priv->freq_offset
...
xc4000_get_frequency() and xc4000_set_params() may execute concurrently,
risking inconsistent reads of priv->freq_hz and priv->freq_offset. Since
these related data may update during reading, it can result in incorrect
frequency calculation, leading to atomicity violations.
This possible bug is found by an experimental static analysis tool
developed by our team. This tool analyzes the locking APIs to extract
function pairs that can be concurrently executed, and then analyzes the
instructions in the paired functions to identify possible concurrency bugs
including data races and atomicity violations. The above possible bug is
reported when our tool analyzes the source code of Linux 6.2.
To address this issue, it is proposed to add a mutex lock pair in
xc4000_get_frequency() to ensure atomicity. With this patch applied, our
tool no longer reports the possible bug, with the kernel configuration
allyesconfig for x86_64. Due to the lack of associated hardware, we cannot
test the patch in runtime testing, and just verify it according to the
code logic.
Fixes: 4c07e32884ab6 ("[media] xc4000: Fix get_frequency()")
Reported-by: BassCheck <[email protected]>
Signed-off-by: Gui-Dong Han <[email protected]>
---
drivers/media/tuners/xc4000.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/media/tuners/xc4000.c b/drivers/media/tuners/xc4000.c
index 57ded9ff3f04..29bc63021c5a 100644
--- a/drivers/media/tuners/xc4000.c
+++ b/drivers/media/tuners/xc4000.c
@@ -1515,10 +1515,10 @@ static int xc4000_get_frequency(struct dvb_frontend *fe, u32 *freq)
{
struct xc4000_priv *priv = fe->tuner_priv;
+ mutex_lock(&priv->lock);
*freq = priv->freq_hz + priv->freq_offset;
if (debug) {
- mutex_lock(&priv->lock);
if ((priv->cur_fw.type
& (BASE | FM | DTV6 | DTV7 | DTV78 | DTV8)) == BASE) {
u16 snr = 0;
@@ -1529,8 +1529,8 @@ static int xc4000_get_frequency(struct dvb_frontend *fe, u32 *freq)
return 0;
}
}
- mutex_unlock(&priv->lock);
}
+ mutex_unlock(&priv->lock);
dprintk(1, "%s()\n", __func__);
--
2.34.1
On Thu, Dec 21, 2023 at 06:37:07PM +0800, Gui-Dong Han wrote:
> In xc4000_get_frequency():
> *freq = priv->freq_hz + priv->freq_offset;
> The code accesses priv->freq_hz and priv->freq_offset without holding any
> lock.
>
> In xc4000_set_params():
> // Code that updates priv->freq_hz and priv->freq_offset
> ...
>
> xc4000_get_frequency() and xc4000_set_params() may execute concurrently,
> risking inconsistent reads of priv->freq_hz and priv->freq_offset. Since
> these related data may update during reading, it can result in incorrect
> frequency calculation, leading to atomicity violations.
>
> This possible bug is found by an experimental static analysis tool
> developed by our team. This tool analyzes the locking APIs to extract
> function pairs that can be concurrently executed, and then analyzes the
> instructions in the paired functions to identify possible concurrency bugs
> including data races and atomicity violations. The above possible bug is
> reported when our tool analyzes the source code of Linux 6.2.
>
> To address this issue, it is proposed to add a mutex lock pair in
> xc4000_get_frequency() to ensure atomicity. With this patch applied, our
> tool no longer reports the possible bug, with the kernel configuration
> allyesconfig for x86_64. Due to the lack of associated hardware, we cannot
> test the patch in runtime testing, and just verify it according to the
> code logic.
>
> Fixes: 4c07e32884ab6 ("[media] xc4000: Fix get_frequency()")
> Reported-by: BassCheck <[email protected]>
> Signed-off-by: Gui-Dong Han <[email protected]>
> ---
> drivers/media/tuners/xc4000.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
Hi,
This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him
a patch that has triggered this response. He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created. Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.
You are receiving this message because of the following common error(s)
as indicated below:
- You have marked a patch with a "Fixes:" tag for a commit that is in an
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applied to any older kernel releases. To properly fix this, please
follow the documented rules in the
Documentation/process/stable-kernel-rules.rst file for how to resolve
this.
If you wish to discuss this problem further, or you have questions about
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Greg will reply once he has dug out from the pending patches received
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thanks,
greg k-h's patch email bot