[PATCH v3 4/5] fs/ntfs: Correct possible infinite loops / hangs

[Andrew Hamilton <adhamilt@gmail.com>]

Correct several infinite loops / hangs found during fuzzing.
The issues fixed here could occur if certain specific malformed NTFS
file systems were presented to GRUB. Currently, GRUB does not allow NTFS
file system access when lockdown mode is enforced, so these should be of
minimal impact.

The changes made in this commit generally correct issues such as attempting
to iterate through a buffer using a length read from the NTFS file system
without confirming the length is larger than 0.

Signed-off-by: Andrew Hamilton <adhamilt@gmail.com>
---
 grub-core/fs/ntfs.c | 33 +++++++++++++++++++++++++++++----
 1 file changed, 29 insertions(+), 4 deletions(-)

diff --git a/grub-core/fs/ntfs.c b/grub-core/fs/ntfs.c
index 5f7a1ecc9..5b0a18f3d 100644
--- a/grub-core/fs/ntfs.c
+++ b/grub-core/fs/ntfs.c
@@ -428,7 +428,7 @@ find_attr (struct grub_ntfs_attr *at, grub_uint8_t attr)
 
       if (*at->attr_cur == GRUB_NTFS_AT_ATTRIBUTE_LIST)
 	at->attr_end = at->attr_cur;
-      if ((*at->attr_cur == attr) || (attr == 0))
+      if ((*at->attr_cur == attr) || (attr == 0) || (nsize == 0))
 	return at->attr_cur;
       at->attr_cur = at->attr_nxt;
     }
@@ -563,6 +563,7 @@ locate_attr (struct grub_ntfs_attr *at, struct grub_ntfs_file *mft,
 	     grub_uint8_t attr)
 {
   grub_uint8_t *pa;
+  grub_uint8_t *last_pa;
 
   if (init_attr (at, mft) != GRUB_ERR_NONE)
     return NULL;
@@ -572,13 +573,16 @@ locate_attr (struct grub_ntfs_attr *at, struct grub_ntfs_file *mft,
     return NULL;
   if ((at->flags & GRUB_NTFS_AF_ALST) == 0)
     {
+      /* Used to make sure we're not stuck in a loop. */
+      last_pa = NULL;
       while (1)
 	{
 	  pa = find_attr (at, attr);
-	  if (pa == NULL)
+	  if (pa == NULL || pa == last_pa)
 	    break;
 	  if (at->flags & GRUB_NTFS_AF_ALST)
 	    return pa;
+	  last_pa = pa;
 	}
       grub_errno = GRUB_ERR_NONE;
       free_attr (at);
@@ -908,6 +912,7 @@ list_file (struct grub_ntfs_file *diro, grub_uint8_t *pos, grub_uint8_t *end_pos
 {
   grub_uint8_t *np;
   int ns;
+  grub_uint16_t pos_incr;
 
   while (1)
     {
@@ -970,7 +975,12 @@ list_file (struct grub_ntfs_file *diro, grub_uint8_t *pos, grub_uint8_t *end_pos
 
 	  grub_free (ustr);
 	}
-      pos += u16at (pos, 8);
+	pos_incr = u16at (pos, 8);
+	if (pos_incr > 0)
+	  pos += pos_incr;
+	else
+	  return 0;
+
     }
   return 0;
 }
@@ -1081,6 +1091,8 @@ grub_ntfs_iterate_dir (grub_fshelp_node_t dir,
   int ret = 0;
   grub_size_t bitmap_len;
   struct grub_ntfs_file *mft;
+  /* Used to make sure we're not stuck in a loop. */
+  grub_uint8_t *last_pos = NULL;
   grub_uint32_t tmp_len;
 
   mft = (struct grub_ntfs_file *) dir;
@@ -1101,11 +1113,12 @@ grub_ntfs_iterate_dir (grub_fshelp_node_t dir,
   while (1)
     {
       cur_pos = find_attr (at, GRUB_NTFS_AT_INDEX_ROOT);
-      if (cur_pos == NULL)
+      if (cur_pos == NULL || cur_pos == last_pos)
 	{
 	  grub_error (GRUB_ERR_BAD_FS, "no $INDEX_ROOT");
 	  goto done;
 	}
+      last_pos = cur_pos;
 
       /* Resident, Namelen=4, Offset=0x18, Flags=0x00, Name="$I30" */
       if ((u32at (cur_pos, 8) != 0x180400) ||
@@ -1133,10 +1146,18 @@ grub_ntfs_iterate_dir (grub_fshelp_node_t dir,
   /* No need to check errors here, as it will already be fine */
   init_attr (at, mft);
 
+  last_pos = NULL;
   while ((cur_pos = find_attr (at, GRUB_NTFS_AT_BITMAP)) != NULL)
     {
       int ofs;
 
+      if (cur_pos == last_pos)
+      {
+        grub_error (GRUB_ERR_BAD_FS, "bitmap attribute loop");
+        goto done;
+      }
+      last_pos = cur_pos;
+
       ofs = cur_pos[0xA];
       /* Namelen=4, Name="$I30" */
       if ((cur_pos[9] == 4) &&
@@ -1201,6 +1222,7 @@ grub_ntfs_iterate_dir (grub_fshelp_node_t dir,
     }
 
   free_attr (at);
+  last_pos = NULL;
   cur_pos = locate_attr (at, mft, GRUB_NTFS_AT_INDEX_ALLOCATION);
   while (cur_pos != NULL)
     {
@@ -1210,6 +1232,9 @@ grub_ntfs_iterate_dir (grub_fshelp_node_t dir,
 	  (u32at (cur_pos, 0x44) == 0x300033))
 	break;
       cur_pos = find_attr (at, GRUB_NTFS_AT_INDEX_ALLOCATION);
+      if (cur_pos == last_pos)
+        break;
+      last_pos = cur_pos;
     }
 
   if ((!cur_pos) && (bitmap))
-- 
2.39.5


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