[PATCH] lib/firmware_table: validate subtable bounds

[Jiale Yao]

The generic firmware table walker dispatches matching entries after only
checking that a generic subtable header is present. A record whose
declared length is shorter than its header or extends past the table can
therefore reach a handler before its bounds have been established.

Validate the complete generic header and the declared record range
before looking up or invoking a handler. This also rejects zero-length
records and prevents malformed lengths from advancing the cursor outside
the table.

Signed-off-by: Jiale Yao <yaojiale02@xxxxxxx>
---
 lib/fw_table.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/lib/fw_table.c b/lib/fw_table.c
index 16291814450e..84c2515edde7 100644
--- a/lib/fw_table.c
+++ b/lib/fw_table.c
@@ -172,7 +172,20 @@ acpi_parse_entries_array(char *id, unsigned long table_size,
 	    ((unsigned long)table_header + table_size);
 	subtable_len = acpi_get_subtable_header_length(&entry);
 
-	while (((unsigned long)entry.hdr) + subtable_len < table_end) {
+	while ((unsigned long)entry.hdr < table_end) {
+		if (table_end - (unsigned long)entry.hdr < subtable_len) {
+			pr_err("[%4.4s] Invalid subtable header\n", id);
+			return -EINVAL;
+		}
+
+		entry_len = acpi_get_entry_length(&entry);
+		if (entry_len < subtable_len ||
+		    entry_len > table_end - (unsigned long)entry.hdr) {
+			pr_err("[%4.4s:0x%02lx] Invalid length %lu\n", id,
+			       acpi_get_entry_type(&entry), entry_len);
+			return -EINVAL;
+		}
+
 		for (i = 0; i < proc_num; i++) {
 			if (acpi_get_entry_type(&entry) != proc[i].id)
 				continue;
@@ -186,16 +199,6 @@ acpi_parse_entries_array(char *id, unsigned long table_size,
 			break;
 		}
 
-		/*
-		 * If entry->length is 0, break from this loop to avoid
-		 * infinite loop.
-		 */
-		entry_len = acpi_get_entry_length(&entry);
-		if (entry_len == 0) {
-			pr_err("[%4.4s:0x%02x] Invalid zero length\n", id, proc->id);
-			return -EINVAL;
-		}
-
 		entry.hdr = (union acpi_subtable_headers *)
 		    ((unsigned long)entry.hdr + entry_len);
 	}
-- 
2.34.1