Re: [PATCHES v4 00/29] perf: Harden perf.data parsing against crafted/corrupted files

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Tue, May 26, 2026 at 06:17:36PM -0300, Arnaldo Carvalho de Melo wrote:
> perf.data validation and hardening (29 patches)
> 
> A crafted or corrupted perf.data file can cause out-of-bounds
> reads/writes, infinite loops, heap overflows, and segfaults in perf
> report, perf script, perf inject, perf timechart, and perf kwork.
> This series adds defense-in-depth validation for file parsing:

The analysis about Sashiko's remaining comments is below, unless someone
has something not related by Sashiko, I'll merge this tomorrow and
continue processing the other outstanding patches.

● Here's the v4 sashiko.dev review triage — 13 of 29 patches got reviews:

  Patches with findings:

  Patch: 02 (peek_event bounds)
  Findings: 1 High: mmap_size - page_offset underflow
  Verdict: Pre-existing — reader__init() validates data_size, page_offset can't exceed mmap_size
  ────────────────────────────────────────
  Patch: 04 (zstd compress)
  Findings: 1 Critical + 3 High: multi-record header overflow, AIO data_size, flush return, decompress pos
  Verdict: All pre-existing — the Critical is about process_header() aggregate size, and the decompress issue is fixed later in patch 05
  ────────────────────────────────────────
  Patch: 05 (zstd decompress)
  Findings: 1 High: O_NONBLOCK missing on file opens
  Verdict: Pre-existing — not introduced by this patch, unrelated to zstd

This one IIRC Ian sent a patch for review-prompts, merged recently that
will make its way to Sashiko and will stop being flagged as a problem:

  "kernel/subsystem/perf.md: Remove section describing non-blocking IO"
  https://github.com/masoncl/review-prompts/commit/261d73261dbb11f38ff9c653da3608b162741e03

  ────────────────────────────────────────
  Patch: 08 (swap infra)
  Findings: 2 High: mmap2 prot/flags not swapped, event_update union not swapped
  Verdict: Both pre-existing — correct observations for follow-up series
  ────────────────────────────────────────
  Patch: 10 (HEADER_ATTR)
  Findings: same as v3 — already triaged
  Verdict:
  ────────────────────────────────────────
  Patch: 11 (nr validation)
  Findings: 1 Medium: native path aborts vs swap path skips on bad THREAD_MAP
  Verdict: Valid observation — but intentional: native path returns -EINVAL to catch corruption, swap path skips to keep session alive.
  ────────────────────────────────────────
  Patch: 12 (build_id_swap)
  Findings: same as v3 — already fixed in v4
  Verdict:
  ────────────────────────────────────────
  Patch: 15 (BPF_METADATA)
  Findings: 1 High new: double-fetch of header.size in swap path; 2 High pre-existing: TOCTOU on native path
  Verdict: The double-fetch is valid for swap but swap runs on MAP_PRIVATE (writable copy), so no concurrent modification possible.
  ────────────────────────────────────────
  Patch: 24 (compressed hardening)
  Findings: 1 Medium: double-fetch of event->header.size in tool.c
  Verdict: Same TOCTOU pattern
  ────────────────────────────────────────
  Patch: 26 (CPU bounds)
  Findings: 1 High: global clamp corrupts data for >4096 CPUs
  Verdict: Known limitation — memory [[MAX_NR_CPUS dynamic allocation]] TODO
  ────────────────────────────────────────
  Patch: 28 (READ_ONCE snapshot)
  Findings: 4 High: incomplete TOCTOU fix, type confusion, array count re-reads
  Verdict: All pre-existing MAP_SHARED TOCTOU. The full fix would be MAP_PRIVATE, noted as follow-up
  ────────────────────────────────────────
  Patch: 29 (shell test)

  Fixed and sent the diff in response to Sashiko's review e-mail.

  Summary: 1 new actionable issue in v4. All the other findings are
  either pre-existing (documented in the cover letter), already fixed in
  this version, or intentional design decisions. The mmap2 prot/flags
  and event_update union swap gaps (patch 08) are valid pre-existing
  bugs for a follow-up series.

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