vim-patch:9.2.0735: [security]: arbitrary Ex command execution during C omni-completion (#40441)

Problem:  [security]: With C omni-completion, a crafted tags file can execute
          arbitrary Ex commands when completing a struct/union member
          (cipher-creator)
Solution: Escape the type field before inserting it into the :vimgrep
          pattern so it cannot close the pattern and start a new command
          (Hirohito Higashi).

Github Security Advisory:
https://github.com/vim/vim/security/advisories/GHSA-mf92-v4xw-j45x

6b611b0d15

Co-authored-by: Hirohito Higashi <h.east.727@gmail.com>

runtime/autoload/ccomplete.vim

@@ -555,7 +555,9 @@ func s:StructMembers(typename, items, all)
       if complete_check()
         return []
       endif
-      exe 'silent! keepj noautocmd ' . n . 'vimgrep /\t' . typename . '\(\t\|$\)/j ' . fnames
+      exe 'silent! keepj noautocmd '
+        \ .. n .. 'vimgrep /\t' .. escape(typename, '/\') .. '\(\t\|$\)/j '
+        \ .. fnames
 
       let qflist = getqflist()
       if len(qflist) > 0 || match(typename, "::") < 0

test/old/testdir/test_plugin_ccomplete.vim

@@ -0,0 +1,62 @@
+" Tests for the C omni-completion plugin (runtime/autoload/ccomplete.vim).
+
+func s:WriteTags(lines)
+  " Mark unsorted so lookup is a linear scan regardless of entry order.
+  let tagsfile = tempname()
+  call writefile(["!_TAG_FILE_SORTED\t0\t/0/"] + a:lines, tagsfile)
+  return tagsfile
+endfunc
+
+" A crafted typeref field is interpolated into the :vimgrep pattern in
+" StructMembers().  Without escaping, "/" closes the pattern and "|" starts a
+" new Ex command, so the field runs as an Ex command during completion.
+func Test_ccomplete_no_exec_via_typeref()
+  unlet! g:ccomplete_injected
+  let tagsfile = s:WriteTags([
+        \ "myvar\tmain.c\t/^x$/;\"\tv\ttyperef:x/|let g:ccomplete_injected = 1|\"",
+        \ ])
+
+  let save_tags = &tags
+  let &tags = tagsfile
+
+  new
+  call ccomplete#Complete(1, '')
+  call ccomplete#Complete(0, 'myvar.x')
+
+  call assert_false(exists('g:ccomplete_injected'),
+        \ 'typeref field was executed as an Ex command during omni-completion')
+
+  bwipe!
+  let &tags = save_tags
+  unlet! g:ccomplete_injected
+endfunc
+
+" A legitimate typeref must still drive struct-member completion: escaping the
+" field value must not break the normal path.
+func Test_ccomplete_typeref_completion_still_works()
+  let tagsfile = s:WriteTags([
+        \ "myvar\tmain.c\t/^x$/;\"\tv\ttyperef:struct:mystruct",
+        \ "alpha\tmain.c\t/^x$/;\"\tm\tstruct:mystruct",
+        \ "beta\tmain.c\t/^x$/;\"\tm\tstruct:mystruct",
+        \ ])
+
+  let save_tags = &tags
+  let &tags = tagsfile
+
+  new
+  call ccomplete#Complete(1, '')
+  let items = ccomplete#Complete(0, 'myvar.')
+
+  call assert_equal(type([]), type(items),
+        \ 'ccomplete#Complete did not return a list')
+  let names = map(copy(items), 'v:val.word')
+  call assert_true(index(names, 'alpha') >= 0,
+        \ 'struct member "alpha" missing from completion: ' . string(names))
+  call assert_true(index(names, 'beta') >= 0,
+        \ 'struct member "beta" missing from completion: ' . string(names))
+
+  bwipe!
+  let &tags = save_tags
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab