[RFC PATCH v2 04/14] kcov: reject enable on multiple dataflow fds simultaneously

A task could enable tracing on multiple kcov_dataflow file descriptors,
corrupting the internal tracking state when one is subsequently closed.

Check current->kcov_df_enabled before allowing KCOV_DF_ENABLE and
return -EBUSY if already active. This matches kcov's check of
t->kcov != NULL in the KCOV_ENABLE path.

Reported-by: sashiko-bot <[email protected]>
Closes: https://sashiko.dev/#/patchset/20260603-kcov-dataflow-next-20260603-v2-0-fee0939de2c4%40est.tech
Signed-off-by: Yunseong Kim <[email protected]>
---
 kernel/kcov_dataflow.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/kcov_dataflow.c b/kernel/kcov_dataflow.c
index 5248293280d5..27587b8ceeab 100644
--- a/kernel/kcov_dataflow.c
+++ b/kernel/kcov_dataflow.c
@@ -287,8 +287,8 @@ static long kcov_df_ioctl(struct file *filep, unsigned int cmd, unsigned long ar
 		break;
 
 	case KCOV_DF_ENABLE:
-		if (!df->area || df->t) {
-			res = -EINVAL;
+		if (!df->area || df->t || current->kcov_df_enabled) {
+			res = -EBUSY;
 			break;
 		}
 		df->t = current;

-- 
2.43.0