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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43796abd259sm11228370f8f.24.2026.02.13.23.32.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Feb 2026 23:32:08 -0800 (PST) From: David Carlier To: Tejun Heo , David Vernet , Andrea Righi Cc: linux-kernel@vger.kernel.org, David Carlier Subject: [PATCH] tools/sched_ext: scx_flatcg: fix heap buffer overflow and memory leak in fcg_read_stats Date: Sat, 14 Feb 2026 07:32:05 +0000 Message-ID: <20260214073205.14498-1-devnexen@gmail.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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: David Carlier --- tools/sched_ext/scx_flatcg.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/tools/sched_ext/scx_flatcg.c b/tools/sched_ext/scx_flatcg.c index bea76d060201..a8446509949e 100644 --- a/tools/sched_ext/scx_flatcg.c +++ b/tools/sched_ext/scx_flatcg.c @@ -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) -- 2.51.0