Pool section entries for DWP version 1

Ref: https://gcc.gnu.org/wiki/DebugFissionDWP?action=recall&rev=3

Fuzzers have found a weakness in the code stashing pool section
entries.  With random nonsensical values in the index entries (rather
than each index pointing to its own set distinct from other sets),
it's possible to overflow the space allocated, losing the NULL
terminator.  Without a terminator, find_section_in_set can run off the
end of the shndx_pool buffer.  Fix this by scanning the pool directly.

binutils/
	* dwarf.c (add_shndx_to_cu_tu_entry): Delete range check.
	(end_cu_tu_entry): Likewise.
	(process_cu_tu_index): Fill shndx_pool by directly scanning
	pool, rather than indirectly from index entries.

binutils/dwarf.c

@@ -10652,22 +10652,12 @@ prealloc_cu_tu_list (unsigned int nshndx)
 static void
 add_shndx_to_cu_tu_entry (unsigned int shndx)
 {
-  if (shndx_pool_used >= shndx_pool_size)
-    {
-      error (_("Internal error: out of space in the shndx pool.\n"));
-      return;
-    }
   shndx_pool [shndx_pool_used++] = shndx;
 }
 
 static void
 end_cu_tu_entry (void)
 {
-  if (shndx_pool_used >= shndx_pool_size)
-    {
-      error (_("Internal error: out of space in the shndx pool.\n"));
-      return;
-    }
   shndx_pool [shndx_pool_used++] = 0;
 }
 
@@ -10773,53 +10763,55 @@ process_cu_tu_index (struct dwarf_section *section, int do_display)
 
   if (version == 1)
     {
+      unsigned char *shndx_list;
+      unsigned int shndx;
+
       if (!do_display)
-	prealloc_cu_tu_list ((limit - ppool) / 4);
-      for (i = 0; i < nslots; i++)
 	{
-	  unsigned char *shndx_list;
-	  unsigned int shndx;
-
-	  SAFE_BYTE_GET (signature, phash, 8, limit);
-	  if (signature != 0)
+	  prealloc_cu_tu_list ((limit - ppool) / 4);
+	  for (shndx_list = ppool + 4; shndx_list <= limit - 4; shndx_list += 4)
 	    {
-	      SAFE_BYTE_GET (j, pindex, 4, limit);
-	      shndx_list = ppool + j * 4;
-	      /* PR 17531: file: 705e010d.  */
-	      if (shndx_list < ppool)
-		{
-		  warn (_("Section index pool located before start of section\n"));
-		  return 0;
-		}
+	      shndx = byte_get (shndx_list, 4);
+	      add_shndx_to_cu_tu_entry (shndx);
+	    }
+	  end_cu_tu_entry ();
+	}
+      else
+	for (i = 0; i < nslots; i++)
+	  {
+	    SAFE_BYTE_GET (signature, phash, 8, limit);
+	    if (signature != 0)
+	      {
+		SAFE_BYTE_GET (j, pindex, 4, limit);
+		shndx_list = ppool + j * 4;
+		/* PR 17531: file: 705e010d.  */
+		if (shndx_list < ppool)
+		  {
+		    warn (_("Section index pool located before start of section\n"));
+		    return 0;
+		  }
 
-	      if (do_display)
 		printf (_("  [%3d] Signature:  %#" PRIx64 "  Sections: "),
 			i, signature);
-	      for (;;)
-		{
-		  if (shndx_list >= limit)
-		    {
-		      warn (_("Section %s too small for shndx pool\n"),
-			    section->name);
-		      return 0;
-		    }
-		  SAFE_BYTE_GET (shndx, shndx_list, 4, limit);
-		  if (shndx == 0)
-		    break;
-		  if (do_display)
+		for (;;)
+		  {
+		    if (shndx_list >= limit)
+		      {
+			warn (_("Section %s too small for shndx pool\n"),
+			      section->name);
+			return 0;
+		      }
+		    SAFE_BYTE_GET (shndx, shndx_list, 4, limit);
+		    if (shndx == 0)
+		      break;
 		    printf (" %d", shndx);
-		  else
-		    add_shndx_to_cu_tu_entry (shndx);
-		  shndx_list += 4;
-		}
-	      if (do_display)
+		    shndx_list += 4;
+		  }
 		printf ("\n");
-	      else
-		end_cu_tu_entry ();
-	    }
-	  phash += 8;
-	  pindex += 4;
-	}
+	      }
+	    phash += 8;
+	    pindex += 4;
+	  }
     }
   else if (version == 2)
     {