getconf: fix fallback to external (re: c3fec93, 519bb08, 66e1d44)

The previous commit exposed a bug in libcmd's getconf(1) built-in
command. First, note that the 'builtin' built-in command can bind
a libcmd built-in command to any path: for example, 'builtin
/foo/bar/getconf' works. As of 519bb08, path-bound built-ins can
be invoked using their canonical path, not just the command name,
so invoking a command by its path no longer guarantees that an
external command is run. Consequently, if the built-in is bound to
the same path that conf.sh detected for the external command, there
is an infinite recursion ending in a C stack overflow: b_getconf()
in src/lib/libcmd/getconf.c keeps invoking itself via sh_run().

src/lib/libcmd/getconf.c:
- b_getconf(): Use 'command -x' to invoke the fallback getconf
  command to guarantee that no path-bound built-in is run.

src/lib/libast/port/astconf.c:
- Fix another bug found in lookup() while I was tracing the above
  one with ASan: an off-by-one error caused a out-of-bounds access
  just beyond the conf array when looking up certain names. The
  last element is lo + conf_elements - 1, not lo + conf_elements.
- Also fix the confusing way in which these variables are declared.

NEWS

@@ -2,6 +2,11 @@ This documents significant changes in the 1.0 branch of ksh 93u+m.
 For full details, see the git log at: https://github.com/ksh93/ksh/tree/1.0
 Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.
 
+2024-03-22:
+
+- Fixed a crash in the getconf built-in that could occur after the 'builtin'
+  command was used to bind it to the same path as the external getconf command.
+
 2024-03-20:
 
 - Android with Termux is now a supported environment for ksh 93u+m. Testing

src/cmd/ksh93/include/version.h

@@ -18,7 +18,7 @@
 
 #define SH_RELEASE_FORK	"93u+m"		/* only change if you develop a new ksh93 fork */
 #define SH_RELEASE_SVER	"1.0.9-beta"	/* semantic version number: https://semver.org */
-#define SH_RELEASE_DATE	"2024-03-20"	/* must be in this format for $((.sh.version)) */
+#define SH_RELEASE_DATE	"2024-03-22"	/* must be in this format for $((.sh.version)) */
 #define SH_RELEASE_CPYR	"(c) 2020-2024 Contributors to ksh " SH_RELEASE_FORK
 
 /* Scripts sometimes field-split ${.sh.version}, so don't change amount of whitespace. */

src/cmd/ksh93/tests/path.sh

@@ -318,6 +318,7 @@ if builtin getconf 2> /dev/null; then
 fi
 
 PATH=$path
+builtin -d /bin/getconf
 
 scr=$tmp/script
 exp=126
@@ -1022,5 +1023,19 @@ got=${ whence -t whence_t_test 2>&1; }
 got=${ type -t whence_t_test 2>&1; }
 [[ $got == "$exp" ]] || err_exit "incorrect 'type -t' output for undefined function (expected '$exp', got '$got')"
 
+# ======
+(
+	builtin getconf 2>/dev/null || exit 1
+	p=$(getconf GETCONF)
+	[[ $p == /*/getconf ]] || exit 2
+	builtin -d getconf
+	builtin "$p"
+	PATH=${p%/getconf}
+	getconf some_nonexistent_config_variable  # be sure to trigger fallback to external command
+	exit 0
+) >/dev/null 2>&1
+(((e = $?) > 1)) && err_exit 'getconf builtin fails when on same path as external getconf' \
+	"(got status $e$( ((e>128)) && print -n /SIG && kill -l "$e"))"
+
 # ======
 exit $((Errors<125?Errors:125))

src/lib/libast/port/astconf.c

@@ -790,9 +790,9 @@ feature(Feature_t* fp, const char* name, const char* path, const char* value, un
 static int
 lookup(Lookup_t* look, const char* name, unsigned int flags)
 {
-	Conf_t*		mid = (Conf_t*)conf;
-	Conf_t*		lo = mid;
-	Conf_t*		hi = mid + conf_elements;
+	Conf_t*		lo = (Conf_t*)conf;
+	Conf_t*		mid = lo;
+	Conf_t*		hi = lo + conf_elements - 1;
 	int		v = 0;
 	int		c;
 	char*		e;

src/lib/libcmd/getconf.c

@@ -139,6 +139,7 @@ b_getconf(int argc, char** argv, Shbltin_t* context)
 	int			flags;
 	int			n;
 	char**			oargv;
+	char**			new_argv;
 	static const char	empty[] = "-";
 
 	cmdinit(argc, argv, context, ERROR_CATALOG, 0);
@@ -274,8 +275,12 @@ b_getconf(int argc, char** argv, Shbltin_t* context)
 	/*
 	 * Run the external getconf command
 	 */
-	oargv[0] = native;
-	if ((n = sh_run(context, argc, oargv)) >= EXIT_NOEXEC)
+	new_argv = stkalloc(stkstd, (argc + 3) * sizeof(char*));
+	new_argv[0] = "command";
+	new_argv[1] = "-x";
+	new_argv[2] = native;
+	memcpy(new_argv + 3, oargv + 1, argc * sizeof(char*));
+	if ((n = sh_run(context, argc + 2, new_argv)) >= EXIT_NOEXEC)
 		error(ERROR_SYSTEM|2, "%s: exec error [%d]", native, n);
 	return n;
 }