Handle strange format strings better.

Make sure that the allocated buffers are not zero sized even for an empty
format string. Also do not call strftime if the buffer is empty. The return
value of strftime does not distinguish between an empty format string and
an overflow of the output buffer. Finally auto scale the size of the outbuf
in case strftime fails. Some format specifiers expand to 25 and more chars
so it is hard to guess in advance what size is required.
This may waste some memory but it keeps the code as simple as possible.
OK tb@

1 files changed, 13 insertions, 7 deletions

diff --git a/usr.bin/ts/ts.c b/usr.bin/ts/ts.c
index 5bb55939f3f..ccfe21f8b17 100644
--- a/usr.bin/ts/ts.c
+++ b/usr.bin/ts/ts.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ts.c,v 1.7 2022/07/06 07:59:03 claudio Exp $	*/
+/*	$OpenBSD: ts.c,v 1.8 2022/07/07 10:40:25 claudio Exp $	*/
 /*
  * Copyright (c) 2022 Job Snijders <job@openbsd.org>
  * Copyright (c) 2022 Claudio Jeker <claudio@openbsd.org>
@@ -31,6 +31,7 @@ static char		*format = "%b %d %H:%M:%S";
 static char		*buf;
 static char		*outbuf;
 static size_t		 bufsize;
+static size_t		 obsize;
 
 static void		 fmtfmt(const struct timespec *);
 static void __dead	 usage(void);
@@ -77,14 +78,14 @@ main(int argc, char *argv[])
 	if (argc == 1)
 		format = *argv;
 
-	bufsize = strlen(format);
+	bufsize = strlen(format) + 1;
 	if (bufsize > SIZE_MAX / 10)
 		errx(1, "format string too big");
-
 	bufsize *= 10;
+	obsize = bufsize;
 	if ((buf = calloc(1, bufsize)) == NULL)
 		err(1, NULL);
-	if ((outbuf = calloc(1, bufsize)) == NULL)
+	if ((outbuf = calloc(1, obsize)) == NULL)
 		err(1, NULL);
 
 	/* force UTC for interval calculations */
@@ -165,9 +166,14 @@ fmtfmt(const struct timespec *ts)
 		}
 	} while (*f != '\0');
 
-	if (strftime(outbuf, bufsize, buf, tm) == 0)
-		errx(1, "strftime");
-
+	*outbuf = '\0';
+	if (*buf != '\0') {
+		while (strftime(outbuf, obsize, buf, tm) == 0) {
+			if ((outbuf = reallocarray(outbuf, 2, obsize)) == NULL)
+				err(1, NULL);
+			obsize *= 2;
+		}
+	}
 	fprintf(stdout, "%s ", outbuf);
 	if (ferror(stdout))
 		exit(1);