[PATCHES v4 00/11] perf tools: Assorted fixes

[Arnaldo Carvalho de Melo]

Hi,

Sixth batch of pre-existing bug fixes found by sashiko-bot AI review
during the perf-data-validation hardening series.  All bugs are latent
in existing code — none were introduced by the hardening patches.

Three broad categories:

1. snprintf() accumulation overflows (patches 2, 8, 9, 10):

   Several functions accumulate formatted output via ret += snprintf().
   snprintf() returns the would-have-been-written count, so on truncation
   ret overshoots the buffer size and the next 'size - ret' underflows
   to a huge unsigned value, disabling bounds checking.  Switched to
   scnprintf() which returns actual bytes written.

   Affected: cpu_map__snprint(), snprintf_hex(),
   synthesize_bpf_prog_name(), hists__scnprintf_title(),
   build_id__snprintf(), hwmon_pmu__describe_items().

2. Missing safety checks on untrusted data (patches 1, 3, 5, 6):

   - get_max_num(): size_t underflow on empty sysfs file causes heap
     over-read.
   - machine__resolve(): unguarded env->cpu[] access with untrusted
     CPU index — switched to perf_env__get_cpu_topology() accessor,
     added bounds check before int16_t truncation.
   - timehist: test_bit(prio, ...) without bounds check on untrusted
     tracepoint priority.
   - idle-hist: rb_first_cached() on a tree populated with plain
     rb_insert_color() — rb_leftmost never set, callchains silently
     dropped.

3. Resource hygiene (patches 4, 7):

   - bitmap_free() without NULLing the pointer (2 call sites).
   - O_CLOEXEC missing from open() calls in DSO and ELF code
     (12 call sites across 2 files).

Patch 11 expands the libperf ABI TODO with the code simplification
argument for widening struct perf_cpu.cpu — the int16_t forces
truncation checks at every boundary where wider CPU indices are
narrowed.

Arnaldo Carvalho de Melo (11):
  perf tools: Fix get_max_num() size_t underflow on empty sysfs file
  perf tools: Use scnprintf() in cpu_map__snprint() to prevent overflow
  perf tools: Use perf_env__get_cpu_topology() in machine__resolve()
  perf tools: NULL bitmap pointers after bitmap_free()
  perf sched: Bounds-check prio before test_bit() in timehist
  perf sched: Fix idle-hist callchain display using wrong rb_first variant
  perf tools: Add O_CLOEXEC to open() calls in DSO and ELF code
  perf bpf: Use scnprintf() in snprintf_hex() and synthesize_bpf_prog_name()
  perf hists: Fix snprintf() in hists__scnprintf_title() UID filter path
  perf tools: Use scnprintf() in build_id__snprintf() and hwmon read_events()
  libperf: Document code simplification case for widening struct perf_cpu

 tools/lib/perf/TODO          |  8 ++++++++
 tools/perf/builtin-record.c  |  1 +
 tools/perf/builtin-sched.c   |  7 +++++--
 tools/perf/util/bpf-event.c  | 11 ++++++-----
 tools/perf/util/build-id.c   |  4 ++--
 tools/perf/util/cpumap.c     | 24 +++++++++++++++---------
 tools/perf/util/dso.c        |  4 ++--
 tools/perf/util/event.c      | 15 +++++++++++++--
 tools/perf/util/hist.c       |  7 ++++---
 tools/perf/util/hwmon_pmu.c  | 12 ++++++------
 tools/perf/util/mmap.c       |  1 +
 tools/perf/util/symbol-elf.c | 20 ++++++++++----------
 12 files changed, 73 insertions(+), 41 deletions(-)

Changes since v3:
  - Patch 3 (machine__resolve): expanded comment explaining why the
    outer al->cpu < nr_cpus_avail check is needed — the int16_t cast
    to struct perf_cpu silently truncates e.g. 65536 to 0, bypassing
    the accessor's internal bounds check.
    (Ian Rogers review)
  - Patch 10 (build_id__snprintf): fixed loop termination — after
    switching to scnprintf(), offs never reaches bf_size, so the
    loop spun doing zero-byte writes.  Changed condition to
    offs + 1 < bf_size.
    (Found by sashiko-bot, confirmed by Ian Rogers)
  - Patch 11 (TODO wording): fixed "wrap to small positive numbers"
    to "wrap to negative numbers (two's complement)".
    (Found by sashiko-bot, confirmed by Ian Rogers)

Changes since v2:
  - Dropped mbind patch (was v2 patch 4): the original code was
    correct — get_nodes() does --maxnode before computing
    BITS_TO_LONGS, so bitmap_zalloc(node_index + 1) with
    maxnode = node_index + 2 already match.  The commit message
    misstated the kernel-side semantics.
  - Split libperf ABI TODO hunk out of prio patch into standalone
    patch 11.
  - Patch 3 (machine__resolve): bounds-check al->cpu against
    env->nr_cpus_avail before truncating to int16_t struct perf_cpu.
    (Found by sashiko-bot lore review)
  - Patch 4 (was v2 patch 5, bitmap_free): reworded from "Three
    call sites" to "Two call sites" — removed dead store from
    memory_node__delete_nodes() where NULLing a pointer right
    before freeing the containing struct was useless.
    (Found by sashiko-bot lore review)

Changes since v1:
  - Patch 5 (was v1 patch 6): fix prio bounds-check logic — the
    v1 condition (prio < 0 || prio >= MAX_PRIO || !test_bit(...))
    incorrectly skipped events with unknown priority (prio == -1).
    Changed to (prio >= 0 && (prio >= MAX_PRIO || !test_bit(...)))
    to preserve the original pass-through for events without
    priority info.
    (Found by sashiko-bot lore review)

Developed with AI assistance (Claude/sashiko), tagged in commits.

Thanks,

- Arnaldo