From 929d1a24d12822942fd4f9fa83582e27f92de243 Mon Sep 17 00:00:00 2001 From: Jian J Wang Date: Thu, 10 Oct 2019 14:28:36 +0800 Subject: [PATCH] SecurityPkg/DxeImageVerificationLib: avoid bypass in fetching dbx (CVE-2019-14575) REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1608 In timestamp check after the cert is found in db, the original code jumps to 'Done' if any error happens in fetching dbx variable. At any of the jump, VerifyStatus equals to TRUE, which means allowed-by-db. This should not be allowed except to EFI_NOT_FOUND case (meaning dbx doesn't exist), because it could be used to bypass timestamp check. This patch add code to change VerifyStatus to FALSE in the case of memory allocation failure and dbx fetching failure to avoid potential bypass issue. Cc: Jiewen Yao Cc: Chao Zhang Signed-off-by: Jian J Wang Reviewed-by: Jiewen Yao --- .../DxeImageVerificationLib/DxeImageVerificationLib.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c index 1efb2f96cd..ed5dbf26b0 100644 --- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c +++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c @@ -1459,15 +1459,26 @@ IsAllowedByDb ( DbxDataSize = 0; Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1, &gEfiImageSecurityDatabaseGuid, NULL, &DbxDataSize, NULL); if (Status != EFI_BUFFER_TOO_SMALL) { + if (Status != EFI_NOT_FOUND) { + VerifyStatus = FALSE; + } goto Done; } DbxData = (UINT8 *) AllocateZeroPool (DbxDataSize); if (DbxData == NULL) { + // + // Force not-allowed-by-db to avoid bypass + // + VerifyStatus = FALSE; goto Done; } Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1, &gEfiImageSecurityDatabaseGuid, NULL, &DbxDataSize, (VOID *) DbxData); if (EFI_ERROR (Status)) { + // + // Force not-allowed-by-db to avoid bypass + // + VerifyStatus = FALSE; goto Done; } -- 2.39.2