File 0002-AUDIT-0-http-boot-tracker-bug.patch of Package grub2

Overview Repositories Revisions Requests Users Attributes Meta

File 0002-AUDIT-0-http-boot-tracker-bug.patch of Package grub2 (Revision ea21ba93e1732c09087c309717aec4e6)

Currently displaying revision ea21ba93e1732c09087c309717aec4e6 , Show latest

From b5c3492f31a98f5ef0f9bec2c0665ad0b71ad5cb Mon Sep 17 00:00:00 2001
From: Sebastian Krahmer <krahmer@suse.com>
Date: Tue, 28 Nov 2017 17:24:38 +0800
Subject: [PATCH] AUDIT-0: http boot tracker bug

Fixing a memory leak in case of error, and a integer overflow, leading to a
heap overflow due to overly large chunk sizes.

We need to check against some maximum value, otherwise values like 0xffffffff
will eventually lead in the allocation functions to small sized buffers, since
the len is rounded up to the next reasonable alignment. The following memcpy
will then smash the heap, leading to RCE.

This is no big issue for pure http boot, since its going to execute an
untrusted kernel anyway, but it will break trusted boot scenarios, where only
signed code is allowed to be executed.

Signed-off-by: Michael Chang <mchang@suse.com>
---
 grub-core/net/efi/net.c | 4 +++-
 grub-core/net/http.c    | 5 ++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/grub-core/net/efi/net.c b/grub-core/net/efi/net.c
index 0bac343b4..5bc604ff0 100644
--- a/grub-core/net/efi/net.c
+++ b/grub-core/net/efi/net.c
@@ -645,8 +645,10 @@ grub_efihttp_chunk_read (grub_file_t file, char *buf,
 
       rd = efi_net_interface (read, file, chunk, sz);
 
-      if (rd <= 0)
+      if (rd <= 0) {
+	grub_free (chunk);
 	return rd;
+      }
 
       if (buf)
 	{
diff --git a/grub-core/net/http.c b/grub-core/net/http.c
index f182d7b87..5004ecfee 100644
--- a/grub-core/net/http.c
+++ b/grub-core/net/http.c
@@ -31,7 +31,8 @@ GRUB_MOD_LICENSE ("GPLv3+");
 
 enum
   {
-    HTTP_PORT = 80
+    HTTP_PORT = 80,
+    HTTP_MAX_CHUNK_SIZE = 0x80000000
   };
 
 
@@ -78,6 +79,8 @@ parse_line (grub_file_t file, http_data_t data, char *ptr, grub_size_t len)
   if (data->in_chunk_len == 2)
     {
       data->chunk_rem = grub_strtoul (ptr, 0, 16);
+      if (data->chunk_rem > HTTP_MAX_CHUNK_SIZE)
+	  return GRUB_ERR_NET_PACKET_TOO_BIG;
       grub_errno = GRUB_ERR_NONE;
       if (data->chunk_rem == 0)
 	{
-- 
2.12.0

Places

File 0002-AUDIT-0-http-boot-tracker-bug.patch of Package grub2 (Revision ea21ba93e1732c09087c309717aec4e6)

Places