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From:   Ross Lagerwall <ross.lagerwall@citrix.com>
To:     <linux-kernel@vger.kernel.org>
CC:     <linux-acpi@vger.kernel.org>, <linux-efi@vger.kernel.org>,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Len Brown <lenb@kernel.org>, Tony Luck <tony.luck@intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Huang Ying <ying.huang@intel.com>,
        Ross Lagerwall <ross.lagerwall@citrix.com>
Subject: [PATCH v2 1/2] acpi/apei: Fix possible out-of-bounds access to BERT region
Date:   Mon, 28 Jan 2019 10:04:23 +0000
Message-ID: <20190128100424.30278-2-ross.lagerwall@citrix.com>
In-Reply-To: <20190128100424.30278-1-ross.lagerwall@citrix.com>
References: <20190128100424.30278-1-ross.lagerwall@citrix.com>
MIME-Version: 1.0
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Sender: linux-kernel-owner@vger.kernel.org
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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@citrix.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