perf header: Validate f_attr.ids section before use in perf_session__read_header()

perf header: Validate f_attr.ids section before use in perf_session__read_header()

perf_session__read_header() reads f_attr.ids.size from the perf.data
file and divides it by sizeof(u64) to compute nr_ids, which is
declared as int.  No validation is performed on the value before it
is used to allocate arrays and drive a read loop.

On 32-bit architectures, a crafted f_attr.ids.size of 0x100000000
(4 GB) produces nr_ids = 0x20000000, but the allocation size
1 * 0x20000000 * 8 overflows size_t to 0, so zalloc(0) returns a
valid pointer.  The subsequent loop writes 0x20000000 IDs into that
zero-length buffer, corrupting the heap.

On 64-bit, the u64-to-int truncation silently drops high bits,
processing fewer IDs than the file claims.  While not exploitable,
this is a data integrity issue.

Add validation before using f_attr.ids:

- Cap nr_attrs (attrs.size / attr_size) to MAX_NR_ATTRS (1 << 16)
  with overflow-safe u64 comparison before assigning to int
- Reject ids.size not aligned to sizeof(u64)
- Cap ids.size / sizeof(u64) to MAX_IDS_PER_ATTR (1 << 24) to
  prevent int truncation and size_t overflow on 32-bit
- Reject ids sections that extend past the end of the file,
  guarded by S_ISREG() so non-regular files (block devices,
  pipes) are not falsely rejected

Also fix perf_header__getbuffer64() to set errno = EIO when
readn() returns 0 (EOF).  Without this, the out_errno path in
perf_session__read_header() returns -errno which is 0 (success)
on truncated files, causing downstream NULL dereferences.

Reported-by: sashiko-bot@kernel.org # Running on a local machine
Reviewed-by: Ian Rogers <irogers@google.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>