Accesses to ctx->s_frame.width and ctx->s_frame.height should be protected by the lock fimc->lock to guarantee that width and height are consistent. Here is an example in fimc_subdev_get_fmt():
struct fimc_frame *ff = &ctx->s_frame; // Alias mutex_lock(&fimc->lock); mf->width = ff->width; mf->height = ff->height;
However, ctx->s_frame.width and ctx->s_frame.height are accessed without holding the lock fimc->lock in fimc_subdev_set_fmt():
mf->width = ctx->s_frame.width; mf->height = ctx->s_frame.height;
And thus a harmful data race can occur, which can make ctx->s_frame.width inconsistent with ctx->s_frame.height, if ctx->s_frame.height is updated right after ctx->s_frame.width is accessed by another thread.
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 fix this possible data race, the lock operation mutex_lock(&fimc->lock) is moved to the front of the accesses to these two variables. With this patch applied, our tool no longer reports the 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: 88fa8311ee36 ("[media] s5p-fimc: Add support for ISP Writeback ...") Signed-off-by: Tuo Li islituo@gmail.com Cc: stable@vger.kernel.org Reported-by: BassCheck bass@buaa.edu.cn --- drivers/media/platform/samsung/exynos4-is/fimc-capture.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/media/platform/samsung/exynos4-is/fimc-capture.c b/drivers/media/platform/samsung/exynos4-is/fimc-capture.c index a0d43bf892e6..5c8b67f92c65 100644 --- a/drivers/media/platform/samsung/exynos4-is/fimc-capture.c +++ b/drivers/media/platform/samsung/exynos4-is/fimc-capture.c @@ -1546,6 +1546,7 @@ static int fimc_subdev_set_fmt(struct v4l2_subdev *sd, fimc_alpha_ctrl_update(ctx);
fimc_capture_mark_jpeg_xfer(ctx, ffmt->color); + mutex_lock(&fimc->lock); if (fmt->pad == FIMC_SD_PAD_SOURCE) { ff = &ctx->d_frame; /* Sink pads crop rectangle size */ @@ -1555,7 +1556,6 @@ static int fimc_subdev_set_fmt(struct v4l2_subdev *sd, ff = &ctx->s_frame; }
- mutex_lock(&fimc->lock); set_frame_bounds(ff, mf->width, mf->height);
if (fmt->pad == FIMC_SD_PAD_SINK_FIFO)