[PATCH v5 01/13] efi/cper: Reject CPER records with an out-of-range error_data_length

cper_estatus_check() sizes each section with acpi_hest_get_record_size(),
which adds the firmware-controlled u32 error_data_length to the header size
as a signed int (see <acpi/ghes.h>). A value in the top sizeof(*gdata)
bytes of the u32 range wraps the sum small rather than large, so it slips
past the "record_size > data_len" check: against the 72-byte v300 header,
0xffffffb9 sizes the record at 1 and acpi_hest_get_next() walks it a byte
at a time, off the end. 0xffffffb8 sizes it at 0 and loops forever.

Use check_add_overflow() to reject a sum that will not fit the int those
helpers return, since the walk advances by that value. That subsumes the
"acpi_hest_get_size(gdata) > data_len" test above it, because record_size
is never smaller than the header.

The later "len < sizeof(*foo)" guards rely on this per-section upper bound;
they are lower bounds only.

Reported-by: [email protected]
Closes: https://sashiko.dev/#/patchset/[email protected]?part=1
Fixes: 45b14a4ffcc1 ("efi: cper: Fix possible out-of-bounds access")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Dave Jiang <[email protected]>
---
v5:
- Use check_add_overflow() rather than a u64 sum plus an INT_MAX test, and
  drop the now-redundant acpi_hest_get_size() bound (Jonathan Cameron).
---
 drivers/firmware/efi/cper.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/firmware/efi/cper.c b/drivers/firmware/efi/cper.c
index 06b4fdb59917..332c78f2d561 100644
--- a/drivers/firmware/efi/cper.c
+++ b/drivers/firmware/efi/cper.c
@@ -752,7 +752,7 @@ EXPORT_SYMBOL_GPL(cper_estatus_check_header);
 int cper_estatus_check(const struct acpi_hest_generic_status *estatus)
 {
 	struct acpi_hest_generic_data *gdata;
-	unsigned int data_len, record_size;
+	unsigned int data_len;
 	int rc;
 
 	rc = cper_estatus_check_header(estatus);
@@ -762,10 +762,18 @@ int cper_estatus_check(const struct acpi_hest_generic_status *estatus)
 	data_len = estatus->data_length;
 
 	apei_estatus_for_each_section(estatus, gdata) {
-		if (acpi_hest_get_size(gdata) > data_len)
+		int record_size;
+
+		/*
+		 * The <acpi/ghes.h> helpers sum these as a signed int, so a
+		 * huge error_data_length wraps small rather than large and the
+		 * walk then advances by that wrapped value. Reject a size an
+		 * int cannot carry.
+		 */
+		if (check_add_overflow(acpi_hest_get_size(gdata),
+				       gdata->error_data_length, &record_size))
 			return -EINVAL;
 
-		record_size = acpi_hest_get_record_size(gdata);
 		if (record_size > data_len)
 			return -EINVAL;
 
-- 
2.54.0