5.4-stable review patch. If anyone has any objections, please let me know.
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From: Gui-Dong Han 2045gemini@gmail.com
[ Upstream commit 36d503ad547d1c75758a6fcdbec2806f1b6aeb41 ]
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, BassCheck[1]. 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.
[1] https://sites.google.com/view/basscheck/
Fixes: 4c07e32884ab ("[media] xc4000: Fix get_frequency()") Cc: stable@vger.kernel.org Reported-by: BassCheck bass@buaa.edu.cn Signed-off-by: Gui-Dong Han 2045gemini@gmail.com Signed-off-by: Hans Verkuil hverkuil-cisco@xs4all.nl Signed-off-by: Sasha Levin sashal@kernel.org --- 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 ef9af052007cb..849df4d1c573c 100644 --- a/drivers/media/tuners/xc4000.c +++ b/drivers/media/tuners/xc4000.c @@ -1517,10 +1517,10 @@ 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; @@ -1531,8 +1531,8 @@ 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__);