Commit cabd76bb authored by David Carlier's avatar David Carlier Committed by Tejun Heo
Browse files

tools/sched_ext: scx_flatcg: fix potential stack overflow from VLA in fcg_read_stats 



fcg_read_stats() had a VLA allocating 21 * nr_cpus * 8 bytes on the
stack, risking stack overflow on large CPU counts (nr_cpus can be up
to 512).

Fix by using a single heap allocation with the correct size, reusing
it across all stat indices, and freeing it at the end.

Signed-off-by: default avatarDavid Carlier <devnexen@gmail.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 0b82cc33

tools/sched_ext/scx_flatcg.c

+9 −4
Original line number Diff line number Diff line
@@ -102,22 +102,27 @@ static float read_cpu_util(__u64 *last_sum, __u64 *last_idle) 


static void fcg_read_stats(struct scx_flatcg *skel, __u64 *stats)

{

	__u64 cnts[FCG_NR_STATS][skel->rodata->nr_cpus];

	__u64 *cnts;

	__u32 idx;



	cnts = calloc(skel->rodata->nr_cpus, sizeof(__u64));

	if (!cnts)

		return;



	memset(stats, 0, sizeof(stats[0]) * FCG_NR_STATS);

	memset(cnts, 0, sizeof(cnts));



	for (idx = 0; idx < FCG_NR_STATS; idx++) {

		int ret, cpu;



		ret = bpf_map_lookup_elem(bpf_map__fd(skel->maps.stats),

					  &idx, cnts[idx]);

					  &idx, cnts);

		if (ret < 0)

			continue;

		for (cpu = 0; cpu < skel->rodata->nr_cpus; cpu++)

			stats[idx] += cnts[idx][cpu];

			stats[idx] += cnts[cpu];

	}



	free(cnts);

}



int main(int argc, char **argv)