util/grub-mkfont: Fix tainted loop boundary issues with substitutions

With gsub substitutions the offsets should be validated against the
number of glyphs in a font face and the memory allocated for the gsub
substitution data.

Both the number of glyphs and the last address in the allocated data are
passed in to process_cursive(), where the number of glyphs validates the end
of the range.

Enabling memory allocation validation uses two macros, one to simply check the
address against the allocated space, and the other to check that the number of
items of a given size doesn't extend outside of the allocated space.

Fixes: CID 73770
Fixes: CID 314040

Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

1 files changed, 53 insertions, 9 deletions

diff --git a/util/grub-mkfont.c b/util/grub-mkfont.c
index d0e5ec564..f07566ade 100644
--- a/util/grub-mkfont.c
+++ b/util/grub-mkfont.c
@@ -67,6 +67,11 @@
 
 #define GRUB_FONT_RANGE_BLOCK		1024
 
+#define GSUB_PTR_VALID(x, end)	assert ((grub_uint8_t *) (x) <= (end))
+
+#define GSUB_ARRAY_SIZE_VALID(a, sz, end) \
+    assert ((sz) >= 0 && ((sz) <= ((end) - (grub_uint8_t *) (a)) / sizeof (*(a))))
+
 struct grub_glyph_info
 {
   struct grub_glyph_info *next;
@@ -487,16 +492,22 @@ subst (const struct gsub_substitution *sub, grub_uint32_t glyph,
 static void
 process_cursive (struct gsub_feature *feature,
 		 struct gsub_lookup_list *lookups,
-		 grub_uint32_t feattag)
+		 grub_uint32_t feattag,
+		 grub_uint32_t num_glyphs,
+		 grub_uint8_t *gsub_end)
 {
   int j, k;
   int i;
+  int lookup_count = grub_be_to_cpu16 (feature->lookupcount);
   struct glyph_replace **target = NULL;
   struct gsub_substitution *sub;
 
-  for (j = 0; j < grub_be_to_cpu16 (feature->lookupcount); j++)
+  GSUB_ARRAY_SIZE_VALID (feature->lookupindices, lookup_count, gsub_end);
+
+  for (j = 0; j < lookup_count; j++)
     {
       int lookup_index = grub_be_to_cpu16 (feature->lookupindices[j]);
+      int sub_count;
       struct gsub_lookup *lookup;
       if (lookup_index >= grub_be_to_cpu16 (lookups->count))
 	{
@@ -538,7 +549,12 @@ process_cursive (struct gsub_feature *feature,
 	  target = &subst_medijoin;
 	  break;
 	}
-      for (k = 0; k < grub_be_to_cpu16 (lookup->subtablecount); k++)
+
+      sub_count = grub_be_to_cpu16 (lookup->subtablecount);
+
+      GSUB_ARRAY_SIZE_VALID (lookup->subtables, sub_count, gsub_end);
+
+      for (k = 0; k < sub_count; k++)
 	{
 	  sub = (struct gsub_substitution *)
 	    ((grub_uint8_t *) lookup + grub_be_to_cpu16 (lookup->subtables[k]));
@@ -559,18 +575,33 @@ process_cursive (struct gsub_feature *feature,
 	  if (covertype == GSUB_COVERAGE_LIST)
 	    {
 	      struct gsub_coverage_list *cover = coverage;
+	      int count = grub_be_to_cpu16 (cover->count);
 	      int l;
-	      for (l = 0; l < grub_be_to_cpu16 (cover->count); l++)
+
+	      GSUB_ARRAY_SIZE_VALID (cover->glyphs, count, gsub_end);
+
+	      for (l = 0; l < count; l++)
 		subst (sub, grub_be_to_cpu16 (cover->glyphs[l]), target, &i);
 	    }
 	  else if (covertype == GSUB_COVERAGE_RANGE)
 	    {
 	      struct gsub_coverage_ranges *cover = coverage;
+	      int count = grub_be_to_cpu16 (cover->count);
 	      int l, m;
-	      for (l = 0; l < grub_be_to_cpu16 (cover->count); l++)
-		for (m = grub_be_to_cpu16 (cover->ranges[l].start);
-		     m <= grub_be_to_cpu16 (cover->ranges[l].end); m++)
-		  subst (sub, m, target, &i);
+
+	      GSUB_ARRAY_SIZE_VALID (cover->ranges, count, gsub_end);
+
+	      for (l = 0; l < count; l++)
+		{
+		  grub_uint16_t start = grub_be_to_cpu16 (cover->ranges[l].start);
+		  grub_uint16_t end = grub_be_to_cpu16 (cover->ranges[l].end);
+
+		  if (start > end || end > num_glyphs)
+		    grub_util_error ("%s", _("invalid font range"));
+
+		  for (m = start; m <= end; m++)
+		    subst (sub, m, target, &i);
+		}
 	    }
 	  else
 	    /* TRANSLATORS: most font transformations apply only to
@@ -589,6 +620,7 @@ add_font (struct grub_font_info *font_info, FT_Face face, int nocut)
 {
   struct gsub_header *gsub = NULL;
   FT_ULong gsub_len = 0;
+  grub_uint8_t *gsub_end = NULL;
 
   if (!FT_Load_Sfnt_Table (face, TTAG_GSUB, 0, NULL, &gsub_len))
     {
@@ -600,6 +632,9 @@ add_font (struct grub_font_info *font_info, FT_Face face, int nocut)
 	  gsub_len = 0;
 	}
     }
+
+  gsub_end = (grub_uint8_t *) gsub + gsub_len;
+
   if (gsub)
     {
       struct gsub_features *features
@@ -610,6 +645,11 @@ add_font (struct grub_font_info *font_info, FT_Face face, int nocut)
 				       + grub_be_to_cpu16 (gsub->lookups_off));
       int i;
       int nfeatures = grub_be_to_cpu16 (features->count);
+
+      GSUB_PTR_VALID (features, gsub_end);
+      GSUB_PTR_VALID (lookups, gsub_end);
+      GSUB_ARRAY_SIZE_VALID (features->features, nfeatures, gsub_end);
+
       for (i = 0; i < nfeatures; i++)
 	{
 	  struct gsub_feature *feature = (struct gsub_feature *)
@@ -617,6 +657,9 @@ add_font (struct grub_font_info *font_info, FT_Face face, int nocut)
 	     + grub_be_to_cpu16 (features->features[i].offset));
 	  grub_uint32_t feattag
 	    = grub_be_to_cpu32 (features->features[i].feature_tag);
+
+	  GSUB_PTR_VALID (feature, gsub_end);
+
 	  if (feature->params)
 	    fprintf (stderr,
 		     _("WARNING: unsupported font feature parameters: %x\n"),
@@ -636,7 +679,8 @@ add_font (struct grub_font_info *font_info, FT_Face face, int nocut)
 	    case FEATURE_FINA:
 	    case FEATURE_INIT:
 	    case FEATURE_MEDI:
-	      process_cursive (feature, lookups, feattag);
+	      process_cursive (feature, lookups, feattag,
+			       face->num_glyphs, gsub_end);
 	      break;
 
 	    default: