patch 9.0.2121: [security]: use-after-free in ex_substitute Commit: https://github.com/vim/vim/commit/26c11c56888d01e298cd8044caf860f3c26f57bb Author: Christian Brabandt <cb@256bit.org> Date: Wed Nov 22 21:26:41 2023 +0100 patch 9.0.2121: [security]: use-after-free in ex_substitute Problem: [security]: use-after-free in ex_substitute Solution: always allocate memory closes: #13552 A recursive :substitute command could cause a heap-use-after free in Vim (CVE-2023-48706). The whole reproducible test is a bit tricky, I can only reproduce this reliably when no previous substitution command has been used yet (which is the reason, the test needs to run as first one in the test_substitute.vim file) and as a combination of the `:~` command together with a :s command that contains the special substitution atom `~\=` which will make use of a sub-replace special atom and calls a vim script function. There was a comment in the existing :s code, that already makes the `sub` variable allocate memory so that a recursive :s call won't be able to cause any issues here, so this was known as a potential problem already. But for the current test-case that one does not work, because the substitution does not start with `\=` but with `~\=` (and since there does not yet exist a previous substitution atom, Vim will simply increment the `sub` pointer (which then was not allocated dynamically) and later one happily use a sub-replace special expression (which could then free the `sub` var). The following commit fixes this, by making the sub var always using allocated memory, which also means we need to free the pointer whenever we leave the function. Since sub is now always an allocated variable, we also do no longer need the sub_copy variable anymore, since this one was used to indicated when sub pointed to allocated memory (and had therefore to be freed on exit) and when not. Github Security Advisory: https://github.com/vim/vim/security/advisories/GHSA-c8qm-x72m-q53q Signed-off-by: Christian Brabandt <cb@256bit.org>

/* vi:set ts=8 sts=4 sw=4 noet:
 *
 * MzScheme interface for Vim, wrapper around scheme.h
 */
#ifndef _IF_MZSCH_H_
#define _IF_MZSCH_H_
#ifdef __MINGW32__
// Hack to engage Cygwin-specific settings
# define __CYGWIN32__
# include <stdint.h>
#endif

#ifdef PROTO
// avoid syntax error for defining Thread_Local_Variables.
# define __thread // empty
#endif

// #ifdef needed for "make depend"
#ifdef FEAT_MZSCHEME
# include <schvers.h>
# include <scheme.h>
#endif

#ifdef __MINGW32__
# undef __CYGWIN32__
#endif

#if MZSCHEME_VERSION_MAJOR >= 299
# define SCHEME_STRINGP(obj) (SCHEME_BYTE_STRINGP(obj) || SCHEME_CHAR_STRINGP(obj))
# define BYTE_STRING_VALUE(obj) ((char_u *)SCHEME_BYTE_STR_VAL(obj))
#else
// macros for compatibility with older versions
# define scheme_current_config() scheme_config
# define scheme_make_sized_byte_string scheme_make_sized_string
# define scheme_format_utf8 scheme_format
# ifndef DYNAMIC_MZSCHEME
// for dynamic MzScheme there will be separate definitions in if_mzsch.c
#  define scheme_get_sized_byte_string_output scheme_get_sized_string_output
#  define scheme_make_byte_string scheme_make_string
#  define scheme_make_byte_string_output_port scheme_make_string_output_port
# endif

# define SCHEME_BYTE_STRLEN_VAL SCHEME_STRLEN_VAL
# define BYTE_STRING_VALUE(obj) ((char_u *)SCHEME_STR_VAL(obj))
# define scheme_byte_string_to_char_string(obj) (obj)
# define SCHEME_BYTE_STRINGP SCHEME_STRINGP
#endif

// Precise GC macros
#ifndef MZ_GC_DECL_REG
# define MZ_GC_DECL_REG(size)		 // empty
#endif
#ifndef MZ_GC_VAR_IN_REG
# define MZ_GC_VAR_IN_REG(x, v)		 // empty
#endif
#ifndef MZ_GC_ARRAY_VAR_IN_REG
# define MZ_GC_ARRAY_VAR_IN_REG(x, v, l) // empty
#endif
#ifndef MZ_GC_REG
# define MZ_GC_REG()			 // empty
#endif
#ifndef MZ_GC_UNREG
# define MZ_GC_UNREG()			 // empty
#endif

#ifdef MZSCHEME_FORCE_GC
/*
 * force garbage collection to check all references are registered
 * seg faults will indicate not registered refs
 */
# define MZ_GC_CHECK() scheme_collect_garbage();
#else
# define MZ_GC_CHECK()			// empty
#endif

#endif // _IF_MZSCH_H_