[PATCH AUTOSEL 6.18-5.10] ACPICA: Enhance buffer validation in acpi_ut_walk_aml_resources()

[Sasha Levin <sashal@kernel.org>]

From: ikaros <void0red@gmail.com>

[ Upstream commit b2e21fe8c3361c3d0d57ee56d359bea9b51fda3d ]

Enhance buffer validation in acpi_ut_walk_aml_resources() to prevent
buffer overflows.

Link: https://github.com/acpica/acpica/commit/975cb20c7992
Signed-off-by: ikaros <void0red@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/2481429.NG923GbCHz@rafael.j.wysocki
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

The background git searches finished and line up with the earlier
analysis:

- **No matching fix in 6.18.44** — searches for “Enhance buffer
  validation” and `AE_AML_BUFFER_LENGTH` usage in `utresrc.c` found
  nothing; the patch is not in this tree yet.
- **Prerequisites are present** — `AE_AML_BUFFER_LENGTH` is already
  defined in `include/acpi/acexcep.h` (since 2018); recent `utresrc.c`
  churn is only pack(1)/alignment work, not this bounds-check fix.
- **Vulnerable code is still there** — the walk loop in
  `acpi_ut_walk_aml_resources()` lacks the new validation.

That supports the **YES** backport verdict for linux-6.18.y: a confirmed
heap-buffer-overflow fix, small and self-contained, with no dependency
blockers in this tree.

 drivers/acpi/acpica/utresrc.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/acpi/acpica/utresrc.c b/drivers/acpi/acpica/utresrc.c
index e1cc3d3487508..86ebd9fb869af 100644
--- a/drivers/acpi/acpica/utresrc.c
+++ b/drivers/acpi/acpica/utresrc.c
@@ -165,6 +165,28 @@ acpi_ut_walk_aml_resources(struct acpi_walk_state *walk_state,
 	/* Walk the byte list, abort on any invalid descriptor type or length */
 
 	while (aml < end_aml) {
+		/*
+		 * Validate that the remaining buffer space can hold enough
+		 * bytes to safely access fields during validation.
+		 * For large resource descriptors (bit 7 set), we need enough
+		 * bytes to access the Type field in serial_bus resources.
+		 * Small resource descriptors only need sizeof(struct aml_resource_end_tag).
+		 */
+		if ((acpi_size)(end_aml - aml) <
+		    sizeof(struct aml_resource_end_tag)) {
+			return_ACPI_STATUS(AE_AML_BUFFER_LENGTH);
+		}
+
+		/*
+		 * For large resource descriptors, ensure enough space for
+		 * the header plus serial_bus Type field access.
+		 */
+		if ((ACPI_GET8(aml) & ACPI_RESOURCE_NAME_LARGE) &&
+		    ((acpi_size)(end_aml - aml) <
+		     ACPI_OFFSET(struct aml_resource_common_serialbus,
+				 type) + 1)) {
+			return_ACPI_STATUS(AE_AML_BUFFER_LENGTH);
+		}
 
 		/* Validate the Resource Type and Resource Length */
 
@@ -182,6 +204,14 @@ acpi_ut_walk_aml_resources(struct acpi_walk_state *walk_state,
 
 		length = acpi_ut_get_descriptor_length(aml);
 
+		/*
+		 * Validate that the descriptor length doesn't exceed the
+		 * remaining buffer size to prevent reading beyond the end.
+		 */
+		if (length > (acpi_size)(end_aml - aml)) {
+			return_ACPI_STATUS(AE_AML_BUFFER_LENGTH);
+		}
+
 		/* Invoke the user function */
 
 		if (user_function) {
-- 
2.53.0