PR27071, gas bugs uncovered by fuzzing

PR 27071
	* config/obj-elf.c (elf_obj_symbol_clone_hook): New function.
	(elf_format_ops): Set symbol_clone_hook.
	* config/obj-elf.h (elf_obj_symbol_clone_hook): Declare.
	(obj_symbol_clone_hook): Define.
	* listing.c (buffer_line): Avoid integer overflow on paper_width
	set to zero.

gas/ChangeLog

@@ -1,3 +1,13 @@
+2020-12-15  Alan Modra  <amodra@gmail.com>
+
+	PR 27071
+	* config/obj-elf.c (elf_obj_symbol_clone_hook): New function.
+	(elf_format_ops): Set symbol_clone_hook.
+	* config/obj-elf.h (elf_obj_symbol_clone_hook): Declare.
+	(obj_symbol_clone_hook): Define.
+	* listing.c (buffer_line): Avoid integer overflow on paper_width
+	set to zero.
+
 2020-12-14  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/gas/elf/section27.s: Reorder .text, .data and .bss

gas/config/obj-elf.c

@@ -2102,6 +2102,22 @@ elf_obj_symbol_new_hook (symbolS *symbolP)
 #endif
 }
 
+/* Deduplicate size expressions.  We might get into trouble with
+   multiple freeing or use after free if we leave them pointing to the
+   same expressionS.  */
+
+void
+elf_obj_symbol_clone_hook (symbolS *newsym, symbolS *orgsym ATTRIBUTE_UNUSED)
+{
+  struct elf_obj_sy *newelf = symbol_get_obj (newsym);
+  if (newelf->size)
+    {
+      expressionS *exp = XNEW (expressionS);
+      *exp = *newelf->size;
+      newelf->size = exp;
+    }
+}
+
 /* When setting one symbol equal to another, by default we probably
    want them to have the same "size", whatever it means in the current
    context.  */
@@ -3088,6 +3104,6 @@ const struct format_ops elf_format_ops =
 #endif
   elf_obj_read_begin_hook,
   elf_obj_symbol_new_hook,
-  0,
+  elf_obj_symbol_clone_hook,
   elf_adjust_symtab
 };

gas/config/obj-elf.h

@@ -223,6 +223,11 @@ void elf_obj_symbol_new_hook (symbolS *);
 #define obj_symbol_new_hook	elf_obj_symbol_new_hook
 #endif
 
+void elf_obj_symbol_clone_hook (symbolS *, symbolS *);
+#ifndef obj_symbol_clone_hook
+#define obj_symbol_clone_hook	elf_obj_symbol_clone_hook
+#endif
+
 void elf_copy_symbol_attributes (symbolS *, symbolS *);
 #ifndef OBJ_COPY_SYMBOL_ATTRIBUTES
 #define OBJ_COPY_SYMBOL_ATTRIBUTES(DEST, SRC) \

gas/listing.c

@@ -508,17 +508,12 @@ buffer_line (file_info_type *file, char *line, unsigned int size)
 	fseek (last_open_file, file->pos, SEEK_SET);
     }
 
-  /* Leave room for null.  */
-  size -= 1;
-
   c = fgetc (last_open_file);
 
   while (c != EOF && c != '\n' && c != '\r')
     {
-      if (count < size)
+      if (++count < size)
 	*p++ = c;
-      count++;
-
       c = fgetc (last_open_file);
     }
 
@@ -536,7 +531,7 @@ buffer_line (file_info_type *file, char *line, unsigned int size)
   if (c == EOF)
     {
       file->at_end = 1;
-      if (count + 2 < size)
+      if (count + 3 < size)
 	{
 	  *p++ = '.';
 	  *p++ = '.';