tools/sched_ext: scx_flatcg: Fix uninitialized stats on allocation failure

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In fcg_read_stats(), the memset() that zeroes the output @stats array
sits after the calloc() failure check. When calloc() fails, the
function returns without writing @stats.

The caller in main() declares acc_stats uninitialized, passes it as
the @stats argument, and then reads it unconditionally:

    __u64 acc_stats[FCG_NR_STATS];
    fcg_read_stats(skel, acc_stats);
    stats[i] = acc_stats[i] - last_stats[i];   // reads garbage

Because fcg_read_stats() returns void, the caller cannot detect the
failure. Reading the uninitialized array is undefined behavior, and
the garbage is further copied into last_stats via memcpy(), corrupting
the baseline used by the next interval.

This regression was introduced by commit cabd76bbc0 ("tools/sched_ext:
scx_flatcg: fix potential stack overflow from VLA in fcg_read_stats"),
which replaced the VLA with calloc() and inserted the failure check
before the existing memset().

Move the memset() above the calloc() failure check so @stats is always
zeroed regardless of allocation outcome.

Fixes: cabd76bbc0 ("tools/sched_ext: scx_flatcg: fix potential stack overflow from VLA in fcg_read_stats")
Signed-off-by: Liang Luo <luoliang@kylinos.cn>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

...

This commit is contained in:

Liang Luo 2026-07-13 15:18:08 +08:00 • committed by Tejun Heo

parent cbcda14b12

commit e07f6bb73e

1 changed files with 2 additions and 2 deletions

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tools/sched_ext/scx_flatcg.c

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