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From d7e857c8a02ae15a940faacc6e8b688cc590c4d7 Mon Sep 17 00:00:00 2001
From: Sebastian Krahmer <krahmer@suse.com>
Date: Tue, 28 Nov 2017 17:24:38 +0800
Subject: [PATCH 248/250] 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 9e0078ac1c6..2bf15447fd5 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 f182d7b871d..5004ecfee42 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)
 	{
-- 
2.14.3