[PATCH v4 02/13] efi/cper: Reject an error status block length that wraps a u32

cper_estatus_len() sums the firmware-controlled data_length (or
raw_data_offset plus raw_data_length) into a u32. A data_length of
0xffffffec wraps that sum to 0, and a length that reads back short defeats
every bound built on it: bert_print_all() passes its "remain <
estatus_len" check, then advances "estatus += estatus_len" by zero and
loops forever. GHES survives only because __ghes_check_estatus() rejects a
length below sizeof(*estatus) first.

Reject a length that cannot be expressed in a u32 in
cper_estatus_check_header(), which both of today's callers reach: GHES via
__ghes_check_estatus() and BERT via cper_estatus_check(). extlog reaches
neither yet; a later patch routes it through cper_estatus_check(), whose
ELOG_ENTRY_LEN bound needs this to hold.

Reported-by: [email protected]
Closes: https://sashiko.dev/#/patchset/[email protected]?part=1
Fixes: 06d65deade9a ("ACPI, APEI, UEFI Common Platform Error Record (CPER) header")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Dave Jiang <[email protected]>
---
v4:
- New patch. sashiko-bot's review of v4 pointed out that the u32 sum in
  cper_estatus_len() wraps, which bypasses the bounds added by the
  surrounding patches.
---
 drivers/firmware/efi/cper.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index ec092729cacc..ea1c999089bc 100644
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -745,6 +745,17 @@ int cper_estatus_check_header(const struct acpi_hest_generic_status *estatus)
 	    estatus->raw_data_offset < sizeof(*estatus) + estatus->data_length)
 		return -EINVAL;
 
+	/*
+	 * cper_estatus_len() sums these into a u32, and a wrapped sum reads
+	 * back smaller than the record. Reject a length that cannot be
+	 * expressed so no caller is handed the short value.
+	 */
+	if ((u64)sizeof(*estatus) + estatus->data_length > U32_MAX)
+		return -EINVAL;
+	if (estatus->raw_data_length &&
+	    (u64)estatus->raw_data_offset + estatus->raw_data_length > U32_MAX)
+		return -EINVAL;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(cper_estatus_check_header);
-- 
2.54.0