[hackers] [sbase][PATCH] printf: Fixes and tweaks

From: Santtu Lakkala <inz_AT_inz.fi>
Date: Wed, 31 Aug 2022 13:08:32 +0300

Allow the use of multiple flags per conversion, as most flags are not
mutually exclusive.

Remove all dynamic memory usage, relying on stack buffer and variables
instead for generated format strings and character arguments.

Fix reading past format string end (with check before strchr) and use
of strtoll.

Only allow %% verbatim and simplify setting cooldown and process all
literal data in one iteration of the loop.

Fix incorrect default "width" value, and allow negative widths via *.

Consume away any length specifiers (l and h).

---
 printf.c | 121 +++++++++++++++++++++++++------------------------------
 1 file changed, 54 insertions(+), 67 deletions(-)
diff --git a/printf.c b/printf.c
index 039dac7..aa0a2df 100644
--- a/printf.c
+++ b/printf.c
_AT_@ -9,6 +9,8 @@
 #include "utf.h"
 #include "util.h"
 
+static const char FLAGS[] = "#0- +";
+
 static void
 usage(void)
 {
_AT_@ -18,12 +20,13 @@ usage(void)
 int
 main(int argc, char *argv[])
 {
-	Rune *rarg;
+	Rune rarg;
+	char fmtbuf[sizeof(FLAGS) + sizeof("%*.*ll")];
 	size_t i, j, argi, lastargi, formatlen, blen;
 	long long num;
 	double dou;
 	int cooldown = 0, width, precision, ret = 0;
-	char *format, *tmp, *arg, *fmt, flag;
+	char *format, *tmp, *arg;
 
 	argv0 = argv[0];
 	if (argc < 2)
_AT_@ -38,40 +41,46 @@ main(int argc, char *argv[])
 	if (formatlen == 0)
 		return 0;
 	lastargi = 0;
-	for (i = 0, argi = 2; !cooldown || i < formatlen; i++, i = cooldown ? i : (i % formatlen)) {
+	for (i = 0, argi = 2;
+	     !cooldown || i < formatlen;
+	     cooldown = argi >= argc, i = (i + 1) % (formatlen + cooldown)) {
+		char flags[sizeof(FLAGS)] = { 0 };
 		if (i == 0) {
 			if (lastargi == argi)
 				break;
 			lastargi = argi;
 		}
 		if (format[i] != '%') {
-			putchar(format[i]);
+			size_t n = strcspn(format + i + 1, "%");
+			fwrite(format + i, sizeof(*format), n + 1, stdout);
+			i += n;
 			continue;
 		}
 
-		/* flag */
-		for (flag = '\0', i++; strchr("#-+ 0", format[i]); i++) {
-			flag = format[i];
+		if (format[++i] == '%') {
+			putchar('%');
+			continue;
 		}
 
+		/* flag */
+		for (; i < formatlen && strchr(FLAGS, format[i]); i++)
+			flags[strcspn(flags, (const char[]){ format[i], '\0' })] = format[i];
+
 		/* field width */
-		width = -1;
+		width = 0;
 		if (format[i] == '*') {
 			if (argi < argc)
-				width = estrtonum(argv[argi++], 0, INT_MAX);
-			else
-				cooldown = 1;
+				width = estrtonum(argv[argi++], INT_MIN, INT_MAX);
 			i++;
 		} else {
-			j = i;
-			for (; strchr("+-0123456789", format[i]); i++);
-			if (j != i) {
-				tmp = estrndup(format + j, i - j);
-				width = estrtonum(tmp, 0, INT_MAX);
-				free(tmp);
-			} else {
-				width = 0;
+			num = strtoll(format + i, &tmp, 10);
+			if (num > INT_MAX) {
+				if (tmp - format - i > INT_MAX)
+					tmp = format + i + INT_MAX;
+				eprintf("field width %.*s not in range\n", (int)(tmp - format - i), format + i);
 			}
+			width = num;
+			i = tmp - format;
 		}
 
 		/* field precision */
_AT_@ -80,33 +89,25 @@ main(int argc, char *argv[])
 			if (format[++i] == '*') {
 				if (argi < argc)
 					precision = estrtonum(argv[argi++], 0, INT_MAX);
-				else
-					cooldown = 1;
 				i++;
 			} else {
-				j = i;
-				for (; strchr("+-0123456789", format[i]); i++);
-				if (j != i) {
-					tmp = estrndup(format + j, i - j);
-					precision = estrtonum(tmp, 0, INT_MAX);
-					free(tmp);
-				} else {
-					precision = 0;
+				num = strtoll(format + i, &tmp, 10);
+				if (num < 0 || num > INT_MAX) {
+					if (tmp - format - i > INT_MAX)
+						tmp = format + i + INT_MAX;
+					eprintf("field precision %.*s not in range\n", (int)(tmp - format - i), format + i);
 				}
+				precision = num;
+				i = tmp - format;
 			}
 		}
 
-		if (format[i] != '%') {
-			if (argi < argc)
-				arg = argv[argi++];
-			else {
-				arg = "";
-				cooldown = 1;
-			}
-		} else {
-			putchar('%');
-			continue;
-		}
+		if (argi < argc)
+			arg = argv[argi++];
+		else
+			arg = "";
+
+		i += strspn(format + i, "hl");
 
 		switch (format[i]) {
 		case 'b':
_AT_@ -121,26 +122,20 @@ main(int argc, char *argv[])
 			break;
 		case 'c':
 			unescape(arg);
-			rarg = ereallocarray(NULL, utflen(arg) + 1, sizeof(*rarg));
-			utftorunestr(arg, rarg);
-			efputrune(rarg, stdout, "<stdout>");
-			free(rarg);
+			chartorune(&rarg, arg);
+			efputrune(&rarg, stdout, "<stdout>");
 			break;
 		case 's':
-			fmt = estrdup(flag ? "%#*.*s" : "%*.*s");
-			if (flag)
-				fmt[1] = flag;
-			printf(fmt, width, precision, arg);
-			free(fmt);
+			snprintf(fmtbuf, sizeof(fmtbuf), "%%%s*.*s", flags);
+			printf(fmtbuf, width, precision, arg);
 			break;
 		case 'd': case 'i': case 'o': case 'u': case 'x': case 'X':
 			for (j = 0; isspace(arg[j]); j++);
 			if (arg[j] == '\'' || arg[j] == '\"') {
 				arg += j + 1;
 				unescape(arg);
-				rarg = ereallocarray(NULL, utflen(arg) + 1, sizeof(*rarg));
-				utftorunestr(arg, rarg);
-				num = rarg[0];
+				chartorune(&rarg, arg);
+				num = rarg;
 			} else if (arg[0]) {
 				errno = 0;
 				if (format[i] == 'd' || format[i] == 'i')
_AT_@ -161,27 +156,19 @@ main(int argc, char *argv[])
 			} else {
 					num = 0;
 			}
-			fmt = estrdup(flag ? "%#*.*ll#" : "%*.*ll#");
-			if (flag)
-				fmt[1] = flag;
-			fmt[flag ? 7 : 6] = format[i];
-			printf(fmt, width, precision, num);
-			free(fmt);
+			snprintf(fmtbuf, sizeof(fmtbuf), "%%%s*.*ll%c", flags, format[i]);
+			printf(fmtbuf, width, precision, num);
 			break;
 		case 'a': case 'A': case 'e': case 'E': case 'f': case 'F': case 'g': case 'G':
-			fmt = estrdup(flag ? "%#*.*#" : "%*.*#");
-			if (flag)
-				fmt[1] = flag;
-			fmt[flag ? 5 : 4] = format[i];
-			dou = (strlen(arg) > 0) ? estrtod(arg) : 0;
-			printf(fmt, width, precision, dou);
-			free(fmt);
+			snprintf(fmtbuf, sizeof(fmtbuf), "%%%s*.*%c", flags, format[i]);
+			dou = *arg ? estrtod(arg) : 0;
+			printf(fmtbuf, width, precision, dou);
 			break;
+		case '\0':
+			eprintf("Missing format specifier.\n");
 		default:
 			eprintf("Invalid format specifier '%c'.\n", format[i]);
 		}
-		if (argi >= argc)
-			cooldown = 1;
 	}
 
 	return fshut(stdout, "<stdout>") | ret;
-- 
2.25.1

Received on Wed Aug 31 2022 - 12:08:32 CEST