perf auxtrace: Harden auxtrace_error event handling

perf auxtrace: Harden auxtrace_error event handling

Fix four issues in PERF_RECORD_AUXTRACE_ERROR handling:

1. auxtrace_error_name() takes a signed int parameter, but e->type
   is __u32.  A crafted value like 0xFFFFFFFF converts to -1, passes
   the bounds check, and causes a negative array index.  Fix by
   changing the parameter to unsigned int.

2. The msg field is printed via %s without a length bound.  The
   min_size table only guarantees fields up to msg (offset 48), so
   a truncated event has zero msg bytes within the event boundary.
   Compute the available msg length from header.size, cap at
   sizeof(e->msg), and use %.*s.

3. fmt >= 2 adds machine_pid and vcpu fields after msg[64].  Older
   files may have fmt >= 2 but an event size that doesn't include
   these fields.  Add a size check in the swap handler to downgrade
   fmt before the conditional field access, and a matching size
   guard in the fprintf path for native-endian events (which are
   mmap'd read-only and can't be modified in place).

4. python_process_auxtrace_error() had the same issues: msg was
   passed to tuple_set_string() unbounded, and machine_pid/vcpu
   were accessed unconditionally without checking fmt or event
   size.  Apply the same bounds checks.

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: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Assisted-by: Claude:claude-opus-4.6-1m
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>