perf session: Add validated swap infrastructure with null-termination checks

perf session: Add validated swap infrastructure with null-termination checks

Change swap callbacks from void to int return so handlers can
propagate errors.  All 28 existing handlers are converted to
return 0 on success, -1 on error.  Three new handlers (KSYMBOL,
BPF_EVENT, HEADER_FEATURE) are added returning int from the
start, with sample_id_all handling for the kernel event types.

event_swap() propagates the return to its callers (process_event
and peek_event), which skip events that fail to swap.

Add perf_event__check_nul() for null-termination enforcement
on the common event delivery path for MMAP, MMAP2, COMM,
CGROUP, and KSYMBOL events.  Events with
unterminated strings are skipped — native-endian files are
mapped read-only, so writing a NUL byte in place would segfault.

Swap handler hardening:

 - Use strnlen bounded by event size (instead of strlen) in
   COMM/MMAP/MMAP2/CGROUP swap handlers, returning -1 on
   unterminated strings.

 - Bounds check text_poke old_len+new_len before computing the
   sample_id offset, returning -1 on overflow.  Use offsetof()
   for the native-path check in machines__deliver_event() since
   sizeof() includes struct padding past the flexible array.

 - Fix PERF_RECORD_SWITCH sample_id_all: non-CPU_WIDE SWITCH
   events have sample_id immediately after the 8-byte header,
   not at sizeof(struct perf_record_switch) which is the
   CPU_WIDE variant size.

 - Fix perf_event__time_conv_swap(): decouple time_cycles and
   time_mask into independent per-field event_contains() checks,
   so each field is only swapped when the event is large enough
   to contain it.  The original code guarded both fields under
   a single time_cycles check, which would swap time_mask on a
   short event that contains time_cycles but not time_mask.

 - Handle ABI0 (attr.size == 0) in perf_event__attr_swap()
   by substituting PERF_ATTR_SIZE_VER0, so bswap_safe()
   correctly swaps VER0 fields instead of skipping everything.

 - peek_events: on swap failure, advance past the malformed
   entry instead of aborting the loop.

Note: the nr-field bounds checks for namespaces, thread_map,
cpu_map, and stat_config arrays are added by a subsequent
patch ("perf session: Validate nr fields against event size
on both swap and common paths").  The HEADER_ATTR attr.size
validation is added by ("perf session: Validate HEADER_ATTR
attr.size before swapping").

By establishing the int-returning swap infrastructure first,
all subsequent hardening patches can use direct error returns
from day one — no poison values, no workarounds for void return.

Changes in v2:
- peek_events: abort instead of skip for AUXTRACE events on
  validation failure — skipping only header.size would land
  inside the raw trace payload, causing subsequent iterations
  to misparse data as events (Reported-by: sashiko-bot@kernel.org)

Fixes: 9aa0bfa370b2 ("perf tools: Handle PERF_RECORD_KSYMBOL")
Fixes: 45178a928a4b ("perf tools: Handle PERF_RECORD_BPF_EVENT")
Fixes: e9def1b2e74e ("perf tools: Add feature header record to pipe-mode")
Reported-by: sashiko-bot@kernel.org # Running on a local machine
Reviewed-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Carrillo-Cisneros <davidcc@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Assisted-by: Claude:claude-opus-4.6-1m
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>