[PATCH v6 0/4] perf: Fix and optimize maps parsing, boundaries, and bounds safety

[Ian Rogers <irogers@google.com>]

It turns out that PATH_MAX is respected by system calls but isn't
respected by file paths in /proc/pid/maps and /proc/pid/smaps. In the
kernel "//toolong" is placed in the filename of mmap/mmap2 events
where the filename is longer than PATH_MAX, do the same in the
mmap/mmap2 synthesis code to avoid overrunning the event buffer -
note, the filename buffer is bounds checked but this makes the
synthesis more similar to the kernel approach. With Gemini's help try
to address other correctness and overrun issues.

V6 addresses review feedback:
- Ensures Patch 2 leaves perf_event__synthesize_modules_maps_cb()
  completely untouched, preserving the pre-existing build ID clearing logic
  in baseline.
- Patch 3 explicitly clears PERF_RECORD_MISC_MMAP_BUILD_ID, build_id, and
  reserved union padding members in module synthesis callbacks to
  guarantee no stale Build-ID state leaks between module synthesis
  iterations.

V5 addresses technical review feedback:
- Clamps pathname buffer sizes in read_proc_maps_line() and module
  synthesis callbacks by subtracting machine->id_hdr_size.
- Casts member array memset destination pointers to
  (char *)event + offsetof(...) across all synthesis handlers.
- Restricts max_filename_len in perf_event__synthesize_mmap2_build_id()
  to the minimum of filename array capacity and union payload space.

V4 addresses review feedback:
- Ensures io__drain_line()'s do-while loop is committed directly in
  Patch 2.

V3 addresses review feedback:
- Updates io__drain_line() loop condition from a while loop to a
  do-while loop.

V2 addresses community review feedback:
- Corrects read_proc_maps_line() and io__drain_line() to safely handle
  already consumed newlines.
- Restores early exit block for timeouts so TIMEOUT flag is emitted
  to tools.
- Removes unused assignment to avoid promoting warnings to build errors.

Ian Rogers (4):
  perf find-map: Remove PATH_MAX 128-byte stack array restriction
  perf synthetic-events: Fix line synchronization, bounds, and
    truncation bugs in proc maps reader
  perf synthetic-events: Fix bounds, stale state, and misc flags in
    kernel module synthesis
  perf synthetic-events: Fix bounds and union member access in mmap2
    build_id synthesis

 tools/perf/util/find-map.c         |  10 +-
 tools/perf/util/synthetic-events.c | 294 ++++++++++++++++++++---------
 2 files changed, 212 insertions(+), 92 deletions(-)

-- 
2.55.0.229.g6434b31f56-goog