analyzer: fix dedupe issue seen with CVE-2005-1689

Whilst analyzing the reproducer for detecting CVE-2005-1689
(krb5-1.4.1's src/lib/krb5/krb/recvauth.c), the analyzer reported
11 double-free diagnostics on lines of the form:

   krb5_xfree(inbuf.data);

with no deduplication occcurring.

The root cause is that the diagnostics each have a COMPONENT_REF for
the inbuf.data, but they are different trees, and the de-duplication
logic was using pointer equality.

This patch replaces the pointer equality tests with calls to a new
pending_diagnostic::same_tree_p, implemented using simple_cst_equal.

With this patch, de-duplication occurs, and only 3 diagnostics are
reported.  The 11 diagnostics are partitioned into 3 dedupe keys,
2 with 2 duplicates and 1 with 7 duplicates.

gcc/analyzer/ChangeLog:
	* diagnostic-manager.cc (saved_diagnostic::operator==): Move here
	from header.  Replace pointer equality test on m_var with call to
	pending_diagnostic::same_tree_p.
	* diagnostic-manager.h (saved_diagnostic::operator==): Move to
	diagnostic-manager.cc.
	* pending-diagnostic.cc (pending_diagnostic::same_tree_p): New.
	* pending-diagnostic.h (pending_diagnostic::same_tree_p): New.
	* sm-file.cc (file_diagnostic::subclass_equal_p): Replace pointer
	equality on m_arg with call to pending_diagnostic::same_tree_p.
	* sm-malloc.cc (malloc_diagnostic::subclass_equal_p): Likewise.
	(possible_null_arg::subclass_equal_p): Likewise.
	(null_arg::subclass_equal_p): Likewise.
	(free_of_non_heap::subclass_equal_p): Likewise.
	* sm-pattern-test.cc (pattern_match::operator==): Likewise.
	* sm-sensitive.cc (exposure_through_output_file::operator==):
	Likewise.
	* sm-taint.cc (tainted_array_index::operator==): Likewise.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/CVE-2005-1689-dedupe-issue.c: New test.

gcc/analyzer/ChangeLog

 2020-01-14  David Malcolm  <dmalcolm@redhat.com>
 
+	* diagnostic-manager.cc (saved_diagnostic::operator==): Move here
+	from header.  Replace pointer equality test on m_var with call to
+	pending_diagnostic::same_tree_p.
+	* diagnostic-manager.h (saved_diagnostic::operator==): Move to
+	diagnostic-manager.cc.
+	* pending-diagnostic.cc (pending_diagnostic::same_tree_p): New.
+	* pending-diagnostic.h (pending_diagnostic::same_tree_p): New.
+	* sm-file.cc (file_diagnostic::subclass_equal_p): Replace pointer
+	equality on m_arg with call to pending_diagnostic::same_tree_p.
+	* sm-malloc.cc (malloc_diagnostic::subclass_equal_p): Likewise.
+	(possible_null_arg::subclass_equal_p): Likewise.
+	(null_arg::subclass_equal_p): Likewise.
+	(free_of_non_heap::subclass_equal_p): Likewise.
+	* sm-pattern-test.cc (pattern_match::operator==): Likewise.
+	* sm-sensitive.cc (exposure_through_output_file::operator==):
+	Likewise.
+	* sm-taint.cc (tainted_array_index::operator==): Likewise.
+
+2020-01-14  David Malcolm  <dmalcolm@redhat.com>
+
 	* diagnostic-manager.cc (dedupe_winners::add): Add logging
 	of deduplication decisions made.
 

gcc/analyzer/diagnostic-manager.cc

@@ -91,6 +91,20 @@ saved_diagnostic::~saved_diagnostic ()
   delete m_d;
 }
 
+bool
+saved_diagnostic::operator== (const saved_diagnostic &other) const
+{
+  return (m_sm == other.m_sm
+	  /* We don't compare m_enode.  */
+	  && m_snode == other.m_snode
+	  && m_stmt == other.m_stmt
+	  /* We don't compare m_stmt_finder.  */
+	  && pending_diagnostic::same_tree_p (m_var, other.m_var)
+	  && m_state == other.m_state
+	  && m_d->equal_p (*other.m_d)
+	  && m_trailing_eedge == other.m_trailing_eedge);
+}
+
 /* class diagnostic_manager.  */
 
 /* diagnostic_manager's ctor.  */

gcc/analyzer/diagnostic-manager.h

@@ -34,18 +34,7 @@ public:
 		    pending_diagnostic *d);
   ~saved_diagnostic ();
 
-  bool operator== (const saved_diagnostic &other) const
-  {
-    return (m_sm == other.m_sm
-	    /* We don't compare m_enode.  */
-	    && m_snode == other.m_snode
-	    && m_stmt == other.m_stmt
-	    /* We don't compare m_stmt_finder.  */
-	    && m_var == other.m_var
-	    && m_state == other.m_state
-	    && m_d->equal_p (*other.m_d)
-	    && m_trailing_eedge == other.m_trailing_eedge);
-  }
+  bool operator== (const saved_diagnostic &other) const;
 
   //private:
   const state_machine *m_sm;

gcc/analyzer/pending-diagnostic.cc

@@ -67,4 +67,13 @@ evdesc::event_desc::formatted_print (const char *fmt, ...) const
   return result;
 }
 
+/* Return true if T1 and T2 are "the same" for the purposes of
+   diagnostic deduplication.  */
+
+bool
+pending_diagnostic::same_tree_p (tree t1, tree t2)
+{
+  return simple_cst_equal (t1, t2) == 1;
+}
+
 #endif /* #if ENABLE_ANALYZER */

gcc/analyzer/pending-diagnostic.h

@@ -169,6 +169,10 @@ class pending_diagnostic
      below for a convenience subclass for implementing this.  */
   virtual bool subclass_equal_p (const pending_diagnostic &other) const = 0;
 
+  /* Return true if T1 and T2 are "the same" for the purposes of
+     diagnostic deduplication.  */
+  static bool same_tree_p (tree t1, tree t2);
+
   /* For greatest precision-of-wording, the various following "describe_*"
      virtual functions give the pending diagnostic a way to describe events
      in a diagnostic_path in terms that make sense for that diagnostic.

gcc/analyzer/sm-file.cc

@@ -96,7 +96,7 @@ public:
 
   bool subclass_equal_p (const pending_diagnostic &base_other) const OVERRIDE
   {
-    return m_arg == ((const file_diagnostic &)base_other).m_arg;
+    return same_tree_p (m_arg, ((const file_diagnostic &)base_other).m_arg);
   }
 
   label_text describe_state_change (const evdesc::state_change &change)

gcc/analyzer/sm-malloc.cc

@@ -102,7 +102,7 @@ public:
 
   bool subclass_equal_p (const pending_diagnostic &base_other) const OVERRIDE
   {
-    return m_arg == ((const malloc_diagnostic &)base_other).m_arg;
+    return same_tree_p (m_arg, ((const malloc_diagnostic &)base_other).m_arg);
   }
 
   label_text describe_state_change (const evdesc::state_change &change)
@@ -282,7 +282,7 @@ public:
   {
     const possible_null_arg &sub_other
       = (const possible_null_arg &)base_other;
-    return (m_arg == sub_other.m_arg
+    return (same_tree_p (m_arg, sub_other.m_arg)
 	    && m_fndecl == sub_other.m_fndecl
 	    && m_arg_idx == sub_other.m_arg_idx);
   }
@@ -373,7 +373,7 @@ public:
   {
     const null_arg &sub_other
       = (const null_arg &)base_other;
-    return (m_arg == sub_other.m_arg
+    return (same_tree_p (m_arg, sub_other.m_arg)
 	    && m_fndecl == sub_other.m_fndecl
 	    && m_arg_idx == sub_other.m_arg_idx);
   }
@@ -499,7 +499,7 @@ public:
     FINAL OVERRIDE
   {
     const free_of_non_heap &other = (const free_of_non_heap &)base_other;
-    return (m_arg == other.m_arg && m_kind == other.m_kind);
+    return (same_tree_p (m_arg, other.m_arg) && m_kind == other.m_kind);
   }
 
   bool emit (rich_location *rich_loc) FINAL OVERRIDE

gcc/analyzer/sm-pattern-test.cc

@@ -78,9 +78,9 @@ public:
 
   bool operator== (const pattern_match &other) const
   {
-    return (m_lhs == other.m_lhs
+    return (same_tree_p (m_lhs, other.m_lhs)
 	    && m_op == other.m_op
-	    && m_rhs == other.m_rhs);
+	    && same_tree_p (m_rhs, other.m_rhs));
   }
 
   bool emit (rich_location *rich_loc) FINAL OVERRIDE

gcc/analyzer/sm-sensitive.cc

@@ -95,7 +95,7 @@ public:
 
   bool operator== (const exposure_through_output_file &other) const
   {
-    return m_arg == other.m_arg;
+    return same_tree_p (m_arg, other.m_arg);
   }
 
   bool emit (rich_location *rich_loc) FINAL OVERRIDE

gcc/analyzer/sm-taint.cc

@@ -100,7 +100,7 @@ public:
 
   bool operator== (const tainted_array_index &other) const
   {
-    return m_arg == other.m_arg;
+    return same_tree_p (m_arg, other.m_arg);
   }
 
   bool emit (rich_location *rich_loc) FINAL OVERRIDE

gcc/testsuite/ChangeLog

+2020-01-14  David Malcolm  <dmalcolm@redhat.com>
+
+	* gcc.dg/analyzer/CVE-2005-1689-dedupe-issue.c: New test.
+
 2020-01-15  Jakub Jelinek  <jakub@redhat.com>
 
 	PR lto/91576

gcc/testsuite/gcc.dg/analyzer/CVE-2005-1689-dedupe-issue.c

+#include <stdlib.h>
+
+typedef struct _krb5_data {
+  char *data;
+} krb5_data;
+
+/* Ensure that we de-duplicate the various paths to reach here,
+   and only emit one diagnostic.  */
+
+void
+recvauth_common(krb5_data inbuf)
+{
+  free(inbuf.data);
+  free(inbuf.data); /* { dg-warning "double-'free'" } */
+  /* { dg-message "2 duplicates" "" { target *-*-* } .-1 } */
+}
+
+void krb5_recvauth(krb5_data inbuf)
+{
+  recvauth_common(inbuf);
+}
+
+void krb5_recvauth_version(krb5_data inbuf)
+{
+  recvauth_common(inbuf);
+}