ar: handle invalid ascii numbers better

The atoi helper handles signed 32-bit integers, and expects the input
strings to be NUL terminated.  Some of the fields are larger than what
signed 32-bit can handle, and none of them are NUL terminated.  The
code currently works because it stops processing once it reaches text
that is not numeric, and the content that follows each field is always
non-numeric (e.g. a space).

Add a helper function that leverages strtoll as all of the fields can
fit into a signed 64-bit number.  If the number is invalid, flag it as
such, and normalize it to 0 so the rest of the code can continue on.

Bug: https://bugs.gentoo.org/890577
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

paxinc.c

@@ -50,6 +50,42 @@ archive_handle *ar_open(const char *filename, bool verbose)
 	return ret;
 }
 
+static uint64_t ar_read_ascii_number(const char *numstr, size_t ndigits, int base)
+{
+	/* Largest field ar headers have is 16 bytes. */
+	char buf[17];
+	char *endp;
+	long long ret;
+
+	memcpy(buf, numstr, ndigits);
+	buf[ndigits] = '\0';
+
+	ret = strtoll(buf, &endp, base);
+	/* Numbers are padded with whitespace. */
+	if (*endp != '\0' && *endp != ' ') {
+		warn("ar: invalid number: %s", buf);
+		ret = 0;
+	}
+
+	/*
+	 * Unsigned 64-bit numbers use up to 20 digits, and signed 64-bit numbers use
+	 * up to 19 digits, but ndigits is always less than that.  So we'd never handle
+	 * a number that requires all 64-bits.  If it's negative, it's because the input
+	 * was negative e.g. "-1", and none of these fields should ever be negative.
+	 */
+	if (ret < 0) {
+		warn("ar: invalid number: %s", buf);
+		ret = 0;
+	}
+
+	return ret;
+}
+#define read_octal_number(s, n) ar_read_ascii_number(s, n, 8)
+#define read_decimal_number(s, n) ar_read_ascii_number(s, n, 10)
+/* For char[] arrays rather than dynamic pointers. */
+#define read_octal_number_fixed(s) read_octal_number(s, sizeof(s))
+#define read_decimal_number_fixed(s) read_decimal_number(s, sizeof(s))
+
 archive_member *ar_next(archive_handle *ar)
 {
 	char *s;
@@ -84,12 +120,13 @@ archive_member *ar_next(archive_handle *ar)
 		goto close_and_ret;
 	}
 
+	/* System V extended filename section. */
 	if (ret.buf.formatted.name[0] == '/' && ret.buf.formatted.name[1] == '/') {
 		if (ar->extfn != NULL) {
 			warn("%s: Duplicate GNU extended filename section", ar->filename);
 			goto close_and_ret;
 		}
-		len = atoi(ret.buf.formatted.size);
+		len = read_decimal_number_fixed(ret.buf.formatted.size);
 		ar->extfn = xmalloc(sizeof(char) * (len + 1));
 		if (read(ar->fd, ar->extfn, len) != len)
 			goto close_and_ret;
@@ -104,7 +141,7 @@ archive_member *ar_next(archive_handle *ar)
 	s = ret.buf.formatted.name;
 	if (s[0] == '#' && s[1] == '1' && s[2] == '/') {
 		/* BSD extended filename, always in use on Darwin */
-		len = atoi(s + 3);
+		len = read_decimal_number(s + 3, sizeof(ret.buf.formatted.name) - 3);
 		if (len <= (ssize_t)sizeof(ret.buf.formatted.name)) {
 			if (read(ar->fd, ret.buf.formatted.name, len) != len)
 				goto close_and_ret;
@@ -120,18 +157,18 @@ archive_member *ar_next(archive_handle *ar)
 			warn("%s: GNU extended filename without special data section", ar->filename);
 			goto close_and_ret;
 		}
-		s = ar->extfn + atoi(s + 1);
+		s = ar->extfn + read_decimal_number(s + 1, sizeof(ret.buf.formatted.name) - 1);
 	}
 
 	snprintf(ret.name, sizeof(ret.name), "%s:%s", ar->filename, s);
 	ret.name[sizeof(ret.name) - 1] = '\0';
 	if ((s=strchr(ret.name+strlen(ar->filename), '/')) != NULL)
 		*s = '\0';
-	ret.date = atoi(ret.buf.formatted.date);
-	ret.uid = atoi(ret.buf.formatted.uid);
-	ret.gid = atoi(ret.buf.formatted.gid);
-	ret.mode = strtol(ret.buf.formatted.mode, NULL, 8);
-	ret.size = atoi(ret.buf.formatted.size);
+	ret.date = read_decimal_number_fixed(ret.buf.formatted.date);
+	ret.uid = read_decimal_number_fixed(ret.buf.formatted.uid);
+	ret.gid = read_decimal_number_fixed(ret.buf.formatted.gid);
+	ret.mode = read_octal_number_fixed(ret.buf.formatted.mode);
+	ret.size = read_decimal_number_fixed(ret.buf.formatted.size);
 	ar->skip = ret.size - len;
 
 	return &ret;