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

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Yunseong Kim

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Jun 11, 2026, 12:21:53 PMJun 11

to Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman, Valentin Schneider, K Prateek Nayak, Andrey Konovalov, Alexander Potapenko, Dmitry Vyukov, Andrew Morton, Miguel Ojeda, Boqun Feng, Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross, Danilo Krummrich, Nathan Chancellor, Nicolas Schier, Nick Desaulniers, Bill Wendling, Justin Stitt, Kees Cook, David Hildenbrand, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan, Jonathan Corbet, Shuah Khan, Yunseong Kim, linux-...@vger.kernel.org, kasa...@googlegroups.com, rust-fo...@vger.kernel.org, linux-...@vger.kernel.org, ll...@lists.linux.dev, linu...@kvack.org, linux-k...@vger.kernel.org, work...@vger.kernel.org, linu...@vger.kernel.org, Yeoreum Yun, sashiko-bot

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 <sashi...@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260603-kcov-dataflow-next-20260603-v2-0-fee0939de2c4%40est.tech
Signed-off-by: Yunseong Kim <yunseo...@est.tech>
---
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

Alexander Potapenko

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Jun 12, 2026, 3:33:24 AMJun 12

to Yunseong Kim, Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman, Valentin Schneider, K Prateek Nayak, Andrey Konovalov, Dmitry Vyukov, Andrew Morton, Miguel Ojeda, Boqun Feng, Gary Guo, Björn Roy Baron, Benno Lossin, Andreas Hindborg, Alice Ryhl, Trevor Gross, Danilo Krummrich, Nathan Chancellor, Nicolas Schier, Nick Desaulniers, Bill Wendling, Justin Stitt, Kees Cook, David Hildenbrand, Lorenzo Stoakes, Liam R. Howlett, Vlastimil Babka, Mike Rapoport, Suren Baghdasaryan, Michal Hocko, Shuah Khan, Jonathan Corbet, Shuah Khan, linux-...@vger.kernel.org, kasa...@googlegroups.com, rust-fo...@vger.kernel.org, linux-...@vger.kernel.org, ll...@lists.linux.dev, linu...@kvack.org, linux-k...@vger.kernel.org, work...@vger.kernel.org, linu...@vger.kernel.org, Yeoreum Yun, sashiko-bot

On Thu, Jun 11, 2026 at 6:21 PM Yunseong Kim <yunseo...@est.tech> wrote:
>
> 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 <sashi...@kernel.org>
> Closes: https://sashiko.dev/#/patchset/20260603-kcov-dataflow-next-20260603-v2-0-fee0939de2c4%40est.tech
> Signed-off-by: Yunseong Kim <yunseo...@est.tech>
> ---
> 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