patch 9.0.0577: buffer underflow with unexpected :finally

Problem:    Buffer underflow with unexpected :finally.
Solution:   Check CSF_TRY can be found.

src/ex_eval.c

@@ -1935,23 +1935,23 @@ ex_finally(exarg_T *eap)
     if (cmdmod_error(FALSE))
 	return;
 
-    if (cstack->cs_trylevel <= 0 || cstack->cs_idx < 0)
-	eap->errmsg = _(e_finally_without_try);
-    else
+    for (idx = cstack->cs_idx; idx >= 0; --idx)
+	if (cstack->cs_flags[idx] & CSF_TRY)
+	    break;
+    if (cstack->cs_trylevel <= 0 || idx < 0)
     {
+	eap->errmsg = _(e_finally_without_try);
+	return;
+    }
+
     if (!(cstack->cs_flags[cstack->cs_idx] & CSF_TRY))
     {
 	eap->errmsg = get_end_emsg(cstack);
-	    for (idx = cstack->cs_idx - 1; idx > 0; --idx)
-		if (cstack->cs_flags[idx] & CSF_TRY)
-		    break;
 	// Make this error pending, so that the commands in the following
 	// finally clause can be executed.  This overrules also a pending
 	// ":continue", ":break", ":return", or ":finish".
 	pending = CSTP_ERROR;
     }
-	else
-	    idx = cstack->cs_idx;
 
     if (cstack->cs_flags[idx] & CSF_FINALLY)
     {
@@ -2058,7 +2058,6 @@ ex_finally(exarg_T *eap)
 	cstack->cs_lflags |= CSL_HAD_FINA;
     }
 }
-}
 
 /*
  * ":endtry"
@@ -2076,10 +2075,15 @@ ex_endtry(exarg_T *eap)
     if (cmdmod_error(FALSE))
 	return;
 
-    if (cstack->cs_trylevel <= 0 || cstack->cs_idx < 0)
-	eap->errmsg = _(e_endtry_without_try);
-    else
+    for (idx = cstack->cs_idx; idx >= 0; --idx)
+	if (cstack->cs_flags[idx] & CSF_TRY)
+	    break;
+    if (cstack->cs_trylevel <= 0 || idx < 0)
     {
+	eap->errmsg = _(e_endtry_without_try);
+	return;
+    }
+
     /*
      * Don't do something after an error, interrupt or throw in the try
      * block, catch clause, or finally clause preceding this ":endtry" or
@@ -2099,10 +2103,6 @@ ex_endtry(exarg_T *eap)
 	eap->errmsg = get_end_emsg(cstack);
 
 	// Find the matching ":try" and report what's missing.
-	    idx = cstack->cs_idx;
-	    do
-		--idx;
-	    while (idx > 0 && !(cstack->cs_flags[idx] & CSF_TRY));
 	rewind_conditionals(cstack, idx, CSF_WHILE | CSF_FOR,
 							&cstack->cs_looplevel);
 	skip = TRUE;
@@ -2151,8 +2151,7 @@ ex_endtry(exarg_T *eap)
     // on an interrupt or error not converted to an exception or when
     // a ":break", ":continue", ":return", or ":finish" is pending.  These
     // actions are carried out immediately.
-	if ((rethrow || (!skip
-			&& !(cstack->cs_flags[idx] & CSF_FINALLY)
+    if ((rethrow || (!skip && !(cstack->cs_flags[idx] & CSF_FINALLY)
 		    && !cstack->cs_pending[idx]))
 	    && dbg_check_skipped(eap))
     {
@@ -2199,8 +2198,7 @@ ex_endtry(exarg_T *eap)
      */
     (void)cleanup_conditionals(cstack, CSF_TRY | CSF_SILENT, TRUE);
 
-	if (cstack->cs_idx >= 0
-			       && (cstack->cs_flags[cstack->cs_idx] & CSF_TRY))
+    if (cstack->cs_idx >= 0 && (cstack->cs_flags[cstack->cs_idx] & CSF_TRY))
 	leave_block(cstack);
     --cstack->cs_trylevel;
 
@@ -2255,7 +2253,6 @@ ex_endtry(exarg_T *eap)
 	// Rethrow the current exception (within this cstack).
 	do_throw(cstack);
 }
-}
 
 /*
  * enter_cleanup() and leave_cleanup()

src/testdir/test_trycatch.vim

@@ -3,6 +3,7 @@
 
 source check.vim
 source shared.vim
+import './vim9.vim' as v9
 
 "-------------------------------------------------------------------------------
 " Test environment							    {{{1
@@ -2008,6 +2009,27 @@ func Test_try_catch_errors()
   call assert_fails('try | for i in range(5) | endif | endtry', 'E580:')
   call assert_fails('try | while v:true | endtry', 'E170:')
   call assert_fails('try | if v:true | endtry', 'E171:')
+
+  " this was using a negative index in cstack[]
+  let lines =<< trim END
+      try
+      for
+      if
+      endwhile
+      if
+      finally
+  END
+  call v9.CheckScriptFailure(lines, 'E690:')
+
+  let lines =<< trim END
+      try
+      for
+      if
+      endwhile
+      if
+      endtry
+  END
+  call v9.CheckScriptFailure(lines, 'E690:')
 endfunc
 
 " Test for verbose messages with :try :catch, and :finally                 {{{1

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    577,
 /**/
     576,
 /**/