fs/ntfs: Fix an OOB write when parsing the $ATTRIBUTE_LIST attribute for the $MFT...

When parsing an extremely fragmented $MFT file, i.e., the file described
using the $ATTRIBUTE_LIST attribute, current NTFS code will reuse a buffer
containing bytes read from the underlying drive to store sector numbers,
which are consumed later to read data from these sectors into another buffer.

These sectors numbers, two 32-bit integers, are always stored at predefined
offsets, 0x10 and 0x14, relative to first byte of the selected entry within
the $ATTRIBUTE_LIST attribute. Usually, this won't cause any problem.

However, when parsing a specially-crafted file system image, this may cause
the NTFS code to write these integers beyond the buffer boundary, likely
causing the GRUB memory allocator to misbehave or fail. These integers contain
values which are controlled by on-disk structures of the NTFS file system.

Such modification and resulting misbehavior may touch a memory range not
assigned to the GRUB and owned by firmware or another EFI application/driver.

This fix introduces checks to ensure that these sector numbers are never
written beyond the boundary.

Fixes: CVE-2023-4692
Reported-by: Maxim Suhanov <dfirblog@gmail.com>
Signed-off-by: Maxim Suhanov <dfirblog@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/grub-core/fs/ntfs.c b/grub-core/fs/ntfs.c
index bbdbe24ada83c8a6b40cb52ca4927b26ce6eb737..c3c4db117bba35ec8a6c91bfad4fef24730dbed6 100644 (file)
--- a/grub-core/fs/ntfs.c
+++ b/grub-core/fs/ntfs.c
@@ -184,7 +184,7 @@ find_attr (struct grub_ntfs_attr *at, grub_uint8_t attr)
     }
   if (at->attr_end)
     {
-      grub_uint8_t *pa;
+      grub_uint8_t *pa, *pa_end;
 
       at->emft_buf = grub_malloc (at->mft->data->mft_size << GRUB_NTFS_BLK_SHR);
       if (at->emft_buf == NULL)
@@ -209,11 +209,13 @@ find_attr (struct grub_ntfs_attr *at, grub_uint8_t attr)
            }
          at->attr_nxt = at->edat_buf;
          at->attr_end = at->edat_buf + u32at (pa, 0x30);
+         pa_end = at->edat_buf + n;
        }
       else
        {
          at->attr_nxt = at->attr_end + u16at (pa, 0x14);
          at->attr_end = at->attr_end + u32at (pa, 4);
+         pa_end = at->mft->buf + (at->mft->data->mft_size << GRUB_NTFS_BLK_SHR);
        }
       at->flags |= GRUB_NTFS_AF_ALST;
       while (at->attr_nxt < at->attr_end)
@@ -230,6 +232,13 @@ find_attr (struct grub_ntfs_attr *at, grub_uint8_t attr)
          at->flags |= GRUB_NTFS_AF_GPOS;
          at->attr_cur = at->attr_nxt;
          pa = at->attr_cur;
+
+         if ((pa >= pa_end) || (pa_end - pa < 0x18))
+           {
+             grub_error (GRUB_ERR_BAD_FS, "can\'t parse attribute list");
+             return NULL;
+           }
+
          grub_set_unaligned32 ((char *) pa + 0x10,
                                grub_cpu_to_le32 (at->mft->data->mft_start));
          grub_set_unaligned32 ((char *) pa + 0x14,
@@ -240,6 +249,13 @@ find_attr (struct grub_ntfs_attr *at, grub_uint8_t attr)
            {
              if (*pa != attr)
                break;
+
+              if ((pa >= pa_end) || (pa_end - pa < 0x18))
+                {
+                 grub_error (GRUB_ERR_BAD_FS, "can\'t parse attribute list");
+                 return NULL;
+               }
+
              if (read_attr
                  (at, pa + 0x10,
                   u32at (pa, 0x10) * (at->mft->data->mft_size << GRUB_NTFS_BLK_SHR),