multiboot: validate multiboot header address values

While loading kernel via multiboot-v1 image, (flags & 0x00010000)
indicates that multiboot header contains valid addresses to load
the kernel image. These addresses are used to compute kernel
size and kernel text offset in the OS image. Validate these
address values to avoid an OOB access issue.

This is CVE-2017-14167.

Reported-by: Thomas Garnier <thgarnie@google.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <20170907063256.7418-1-ppandit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/hw/i386/multiboot.c b/hw/i386/multiboot.c
index 6001f4caa29fb0933e241236fb151582419464f6..c7b70c91d51df58eab67dd804377773abcc2cc04 100644 (file)
--- a/hw/i386/multiboot.c
+++ b/hw/i386/multiboot.c
@@ -221,15 +221,34 @@ int load_multiboot(FWCfgState *fw_cfg,
         uint32_t mh_header_addr = ldl_p(header+i+12);
         uint32_t mh_load_end_addr = ldl_p(header+i+20);
         uint32_t mh_bss_end_addr = ldl_p(header+i+24);
+
         mh_load_addr = ldl_p(header+i+16);
+        if (mh_header_addr < mh_load_addr) {
+            fprintf(stderr, "invalid mh_load_addr address\n");
+            exit(1);
+        }
+
         uint32_t mb_kernel_text_offset = i - (mh_header_addr - mh_load_addr);
         uint32_t mb_load_size = 0;
         mh_entry_addr = ldl_p(header+i+28);
 
         if (mh_load_end_addr) {
+            if (mh_bss_end_addr < mh_load_addr) {
+                fprintf(stderr, "invalid mh_bss_end_addr address\n");
+                exit(1);
+            }
             mb_kernel_size = mh_bss_end_addr - mh_load_addr;
+
+            if (mh_load_end_addr < mh_load_addr) {
+                fprintf(stderr, "invalid mh_load_end_addr address\n");
+                exit(1);
+            }
             mb_load_size = mh_load_end_addr - mh_load_addr;
         } else {
+            if (kernel_file_size < mb_kernel_text_offset) {
+                fprintf(stderr, "invalid kernel_file_size\n");
+                exit(1);
+            }
             mb_kernel_size = kernel_file_size - mb_kernel_text_offset;
             mb_load_size = mb_kernel_size;
         }