linux-kernel - [PATCH v2 1/2] acpi/apei: Fix possible out-of-bounds access to BERT region

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Date:   Mon, 28 Jan 2019 10:04:23 +0000
From:   Ross Lagerwall <ross.lagerwall@...rix.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <linux-acpi@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Huang Ying <ying.huang@...el.com>,
        Ross Lagerwall <ross.lagerwall@...rix.com>
Subject: [PATCH v2 1/2] acpi/apei: Fix possible out-of-bounds access to BERT region

Check that the length recorded in the generic error status block is
within the region before checking the contents of the region itself.
Otherwise it may result in an out-of-bounds access if the system
firmware has generated a status block with an invalid length (larger
than the mapped region). Also move the block_status check so that it
only happens after the block has been verified to be within the mapped
region.

Signed-off-by: Ross Lagerwall <ross.lagerwall@...rix.com>
---
 drivers/acpi/apei/bert.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/drivers/acpi/apei/bert.c b/drivers/acpi/apei/bert.c
index 12771fcf0417..0d948d0a41af 100644
--- a/drivers/acpi/apei/bert.c
+++ b/drivers/acpi/apei/bert.c
@@ -42,15 +42,7 @@ static void __init bert_print_all(struct acpi_bert_region *region,
 	int remain = region_len;
 	u32 estatus_len;
 
-	if (!estatus->block_status)
-		return;
-
-	while (remain > sizeof(struct acpi_bert_region)) {
-		if (cper_estatus_check(estatus)) {
-			pr_err(FW_BUG "Invalid error record.\n");
-			return;
-		}
-
+	while (remain >= sizeof(struct acpi_bert_region)) {
 		estatus_len = cper_estatus_len(estatus);
 		if (remain < estatus_len) {
 			pr_err(FW_BUG "Truncated status block (length: %u).\n",
@@ -58,6 +50,15 @@ static void __init bert_print_all(struct acpi_bert_region *region,
 			return;
 		}
 
+		/* No more error records. */
+		if (!estatus->block_status)
+			return;
+
+		if (cper_estatus_check(estatus)) {
+			pr_err(FW_BUG "Invalid error record.\n");
+			return;
+		}
+
 		pr_info_once("Error records from previous boot:\n");
 
 		cper_estatus_print(KERN_INFO HW_ERR, estatus);
@@ -70,10 +71,6 @@ static void __init bert_print_all(struct acpi_bert_region *region,
 		estatus->block_status = 0;
 
 		estatus = (void *)estatus + estatus_len;
-		/* No more error records. */
-		if (!estatus->block_status)
-			return;
-
 		remain -= estatus_len;
 	}
 }
-- 
2.17.2