[PATCH] Fix attribute access issues

[Jakub Jelinek <jakub@redhat.com>]

Hi!

On Thu, Nov 21, 2019 at 06:09:34PM -0700, Martin Sebor wrote:
> > > 	PR middle-end/83859
> > > 	* c-attribs.c (handle_access_attribute): New function.
> > > 	(c_common_attribute_table): Add new attribute.
> > > 	(get_argument_type): New function.
> > > 	(append_access_attrs): New function.

I'm getting
+FAIL: gcc.dg/Wstringop-overflow-24.c (internal compiler error)
+FAIL: gcc.dg/Wstringop-overflow-24.c (test for excess errors)
on i686-linux, while it succeeds on x86_64-linux.  On a closer look,
there is a buffer overflow even on x86_64-linux as can be seen under
valgrind, plus memory leak.

The buffer overflow is in append_access_attrs:
==9759== Command: ./cc1 -quiet -Wall Wstringop-overflow-24.c
==9759== 
==9759== Invalid write of size 1
==9759==    at 0x483BD9F: strcpy (vg_replace_strmem.c:513)
==9759==    by 0xA11FF4: append_access_attrs(tree_node*, tree_node*, char const*, char, long*) (c-attribs.c:3934)
==9759==    by 0xA12AD3: handle_access_attribute(tree_node**, tree_node*, tree_node*, int, bool*) (c-attribs.c:4158)
==9759==    by 0x88E1BF: decl_attributes(tree_node**, tree_node*, int, tree_node*) (attribs.c:728)
==9759==    by 0x8A6A9B: c_decl_attributes(tree_node**, tree_node*, int) (c-decl.c:4944)
==9759==    by 0x8A6FE2: start_decl(c_declarator*, c_declspecs*, bool, tree_node*) (c-decl.c:5083)
==9759==    by 0x91CB15: c_parser_declaration_or_fndef(c_parser*, bool, bool, bool, bool, bool, tree_node**, vec<c_token, va_heap, vl_ptr>, bool, tree_node*, oacc_routine_data*, bool*) (c-parser.c:2216)
==9759==    by 0x91B742: c_parser_external_declaration(c_parser*) (c-parser.c:1690)
==9759==    by 0x91B25E: c_parser_translation_unit(c_parser*) (c-parser.c:1563)
==9759==    by 0x9590A4: c_parse_file() (c-parser.c:21524)
==9759==    by 0x9E308E: c_common_parse_file() (c-opts.c:1185)
==9759==    by 0x1211AEE: compile_file() (toplev.c:458)
==9759==  Address 0x5113f68 is 0 bytes after a block of size 8 alloc'd
==9759==    at 0x483880B: malloc (vg_replace_malloc.c:309)
==9759==    by 0x229BF17: xmalloc (xmalloc.c:147)
==9759==    by 0xA11FC0: append_access_attrs(tree_node*, tree_node*, char const*, char, long*) (c-attribs.c:3932)
==9759==    by 0xA12AD3: handle_access_attribute(tree_node**, tree_node*, tree_node*, int, bool*) (c-attribs.c:4158)
==9759==    by 0x88E1BF: decl_attributes(tree_node**, tree_node*, int, tree_node*) (attribs.c:728)
==9759==    by 0x8A6A9B: c_decl_attributes(tree_node**, tree_node*, int) (c-decl.c:4944)
==9759==    by 0x8A6FE2: start_decl(c_declarator*, c_declspecs*, bool, tree_node*) (c-decl.c:5083)
==9759==    by 0x91CB15: c_parser_declaration_or_fndef(c_parser*, bool, bool, bool, bool, bool, tree_node**, vec<c_token, va_heap, vl_ptr>, bool, tree_node*, oacc_routine_data*, bool*) (c-parser.c:2216)
==9759==    by 0x91B742: c_parser_external_declaration(c_parser*) (c-parser.c:1690)
==9759==    by 0x91B25E: c_parser_translation_unit(c_parser*) (c-parser.c:1563)
==9759==    by 0x9590A4: c_parse_file() (c-parser.c:21524)
==9759==    by 0x9E308E: c_common_parse_file() (c-opts.c:1185)
If n2 != 0, newlen is computed as n1 + n2, but that doesn't take into
account for the , that is added in between the two.

The following patch ought to fix both the buffer overflow (by adding 1 if n2
is non-zero), memory leak (freeing newspec buffer after creating the string;
I've considered using XALLOCAVEC instead, but I believe the string can be
arbitrarily long on functions with thousands of arguments), using XNEWVEC
instead of (type *) xmalloc, using auto_diagnostic_group to bind warning +
inform together and fixes a typo in the documentation.

Ok for trunk if it passes bootstrap/regtest on x86_64-linux and i686-linux?

2019-11-23  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/83859
	* doc/extend.texi (attribute access): Fix a typo.

	* c-attribs.c (append_access_attrs): Avoid buffer overflow.  Avoid
	memory leak.  Use XNEWVEC macro.  Use auto_diagnostic_group to
	group warning with inform together.
	(handle_access_attribute): Formatting fix.

--- gcc/doc/extend.texi.jj	2019-11-22 19:11:53.634970558 +0100
+++ gcc/doc/extend.texi	2019-11-23 01:34:33.344849287 +0100
@@ -2490,7 +2490,7 @@ The following attributes are supported o
 
 The @code{access} attribute enables the detection of invalid or unsafe
 accesses by functions to which they apply to or their callers, as well
-as wite-only accesses to objects that are never read from.  Such accesses
+as write-only accesses to objects that are never read from.  Such accesses
 may be diagnosed by warnings such as @option{-Wstringop-overflow},
 @option{-Wunnitialized}, @option{-Wunused}, and others.
 
--- gcc/c-family/c-attribs.c.jj	2019-11-22 19:11:54.000000000 +0100
+++ gcc/c-family/c-attribs.c	2019-11-23 01:44:50.306617000 +0100
@@ -3840,7 +3840,7 @@ append_access_attrs (tree t, tree attrs,
   if (idxs[1])
     n2 = sprintf (attrspec + n1 + 1, "%u", (unsigned) idxs[1] - 1);
 
-  size_t newlen = n1 + n2;
+  size_t newlen = n1 + n2 + !!n2;
   char *newspec = attrspec;
 
   if (tree acs = lookup_attribute ("access", attrs))
@@ -3869,6 +3869,7 @@ append_access_attrs (tree t, tree attrs,
 	  if (*attrspec != pos[-1])
 	    {
 	      /* Mismatch in access mode.  */
+	      auto_diagnostic_group d;
 	      if (warning (OPT_Wattributes,
 			   "attribute %qs mismatch with mode %qs",
 			   attrstr,
@@ -3884,6 +3885,7 @@ append_access_attrs (tree t, tree attrs,
 	  if ((n2 && pos[n1 - 1] != ','))
 	    {
 	      /* Mismatch in the presence of the size argument.  */
+	      auto_diagnostic_group d;
 	      if (warning (OPT_Wattributes,
 			   "attribute %qs positional argument 2 conflicts "
 			   "with previous designation",
@@ -3897,6 +3899,7 @@ append_access_attrs (tree t, tree attrs,
 	  if (!n2 && pos[n1 - 1] == ',')
 	    {
 	      /* Mismatch in the presence of the size argument.  */
+	      auto_diagnostic_group d;
 	      if (warning (OPT_Wattributes,
 			   "attribute %qs missing positional argument 2 "
 			   "provided in previous designation",
@@ -3910,6 +3913,7 @@ append_access_attrs (tree t, tree attrs,
 	  if (n2 && strncmp (attrstr + n1 + 1, pos + n1, n2))
 	    {
 	      /* Mismatch in the value of the size argument.  */
+	      auto_diagnostic_group d;
 	      if (warning (OPT_Wattributes,
 			   "attribute %qs mismatch positional argument "
 			   "values %i and %i",
@@ -3929,7 +3933,7 @@ append_access_attrs (tree t, tree attrs,
 	attrspec[n1] = ',';
 
       size_t len = strlen (str);
-      newspec = (char *) xmalloc (newlen + len + 1);
+      newspec = XNEWVEC (char, newlen + len + 1);
       strcpy (newspec, str);
       strcpy (newspec + len, attrspec);
       newlen += len;
@@ -3938,7 +3942,10 @@ append_access_attrs (tree t, tree attrs,
     /* Connect the two substrings formatted above into a single one.  */
     attrspec[n1] = ',';
 
-  return build_string (newlen + 1, newspec);
+  tree ret = build_string (newlen + 1, newspec);
+  if (newspec != attrspec)
+    XDELETEVEC (newspec);
+  return ret;
 }
 
 /* Handle the access attribute (read_only, write_only, and read_write).  */
@@ -4168,7 +4175,8 @@ handle_access_attribute (tree *node, tre
     {
       /* Repeat for the previously declared type.  */
       attrs = TYPE_ATTRIBUTES (TREE_TYPE (node[1]));
-      tree new_attrs = append_access_attrs (node[1], attrs, attrstr, code, idxs);
+      tree new_attrs
+	= append_access_attrs (node[1], attrs, attrstr, code, idxs);
       if (!new_attrs)
 	return NULL_TREE;
 


	Jakub