fix(fileio): replace characters over INT_MAX with U+FFFD (#16354)

muniter · web-flow · commit a2e5c2f7c8ec · 2021-11-23T21:07:47.000-07:00
fixes #11877 credit: @zubairabid #12010
diff --git a/src/nvim/fileio.c b/src/nvim/fileio.c
@@ -1360,6 +1360,10 @@ int readfile(char_u *fname, char_u *sfname, linenr_T from, linenr_T lines_to_ski
               u8c += (unsigned)(*--p) << 16;
               u8c += (unsigned)(*--p) << 24;
             }
+            // Replace characters over INT_MAX with Unicode replacement character
+            if (u8c > INT_MAX) {
+              u8c = 0xfffd;
+            }
           } else {        // UTF-8
             if (*--p < 0x80) {
               u8c = *p;
diff --git a/test/functional/core/fileio_spec.lua b/test/functional/core/fileio_spec.lua
@@ -15,6 +15,7 @@ local read_file = helpers.read_file
 local trim = helpers.trim
 local currentdir = helpers.funcs.getcwd
 local iswin = helpers.iswin
+local assert_alive = helpers.assert_alive
 
 describe('fileio', function()
   before_each(function()
@@ -26,6 +27,7 @@ describe('fileio', function()
     os.remove('Xtest_startup_file1~')
     os.remove('Xtest_startup_file2')
     os.remove('Xtest_тест.md')
+    os.remove('Xtest-u8-int-max')
     rmdir('Xtest_startup_swapdir')
     rmdir('Xtest_backupdir')
   end)
@@ -128,5 +130,12 @@ describe('fileio', function()
     table.insert(text, '')
     eq(text, funcs.readfile(fname, 'b'))
   end)
+  it('read invalid u8 over INT_MAX doesn\'t segfault', function()
+    clear()
+    command('call writefile(0zFFFFFFFF, "Xtest-u8-int-max")')
+    -- This should not segfault
+    command('edit ++enc=utf32 Xtest-u8-int-max')
+    assert_alive()
+  end)
 end)
 
