patch 9.0.1873: [security] heap-buffer-overflow in vim_regsub_both

Problem:  heap-buffer-overflow in vim_regsub_both
Solution: Disallow exchanging windows when textlock is active

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/ex_cmds.c

@@ -4519,6 +4519,9 @@ ex_substitute(exarg_T *eap)
 		{
 		    nmatch = curbuf->b_ml.ml_line_count - sub_firstlnum + 1;
 		    skip_match = TRUE;
+		    // safety check
+		    if (nmatch < 0)
+			goto skip;
 		}
 
 		// Need room for:

src/testdir/test_crash.vim

@@ -46,6 +46,7 @@ func Test_crash1()
 
   let file = 'crash/poc_tagfunc.vim'
   let args = printf(cmn_args, vim, file)
+  " using || because this poc causes vim to exit with exitstatus != 0
   call term_sendkeys(buf, args ..
     \ '  || echo "crash 5: [OK]" >> X_crash1_result.txt' .. "\<cr>")
 
@@ -59,6 +60,13 @@ func Test_crash1()
   call delete('X')
   call TermWait(buf, 3000)
 
+  let file = 'crash/vim_regsub_both_poc'
+  let args = printf(cmn_args, vim, file)
+  " using || because this poc causes vim to exit with exitstatus != 0
+  call term_sendkeys(buf, args ..
+    \ '  && echo "crash 7: [OK]" >> X_crash1_result.txt' .. "\<cr>")
+  call TermWait(buf, 1000)
+
   " clean up
   exe buf .. "bw!"
 
@@ -71,6 +79,7 @@ func Test_crash1()
       \ 'crash 4: [OK]',
       \ 'crash 5: [OK]',
       \ 'crash 6: [OK]',
+      \ 'crash 7: [OK]',
       \ ]
 
   call assert_equal(expected, getline(1, '$'))

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1873,
 /**/
     1872,
 /**/

src/window.c

@@ -1733,6 +1733,11 @@ win_exchange(long Prenum)
 	beep_flush();
 	return;
     }
+    if (text_or_buf_locked())
+    {
+	beep_flush();
+	return;
+    }
 
 #ifdef FEAT_GUI
     need_mouse_correct = TRUE;