[PATCH v2 0/2] cpupower: fix topology array handling

[Ali Ahmet Memis <ali@iusegentoo.com>]

v1 did two things in one patch. Shuah asked for them to be split, so here
they are as two.

Patch 1 is the uninitialized read: get_cpu_topology() allocates core_info
with malloc(), several paths never write core_cpu_list, and the sort
comparator then hands that buffer to strcmp(). calloc() fixes it.

Patch 2 is separate and only about the physical core count. The counting
loop seeds cores at 1 from entry 0 without checking whether that entry has
usable topology data, so an incomplete entry can be counted as a core.
Patch 2 depends on patch 1, since it uses an empty core_cpu_list to
recognise an entry that was never filled in.

Tested against a fake sysfs tree with the configured CPU count pinned to 2,
where cpu0 has complete topology and cpu1's topology attributes are absent.
Same harness, one commit apart:

  unpatched     cores=2   valgrind: errors
  patch 1       cores=2   valgrind: clean
  patch 1+2     cores=1   valgrind: clean

Unpatched, valgrind traces it to the allocation:

  Conditional jump or move depends on uninitialised value(s)
     at strcmp (vg_replace_strmem.c:941)
     by __compare_core_cpu_list (cpupower.c:159)
     by qsort_r (qsort.c:409)
     by get_cpu_topology (cpupower.c:214)
   Uninitialised value was created by a heap allocation
     at malloc (vg_replace_malloc.c:446)
     by get_cpu_topology (cpupower.c:174)

I have no machine where a topology attribute actually disappears during
enumeration, so the fake tree is as close as I could get. If you would
rather see this exercised some other way, say so and I will do that.

Link to the v1 review:
https://lore.kernel.org/all/c746110c-6ac4-4500-a4f0-491a06838173@kernel.org/

Ali Ahmet Memis (2):
  cpupower: zero the topology array to avoid uninitialized reads
  cpupower: do not count incomplete topology entries as physical cores

 tools/power/cpupower/lib/cpupower.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

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2.55.0