Have a common routine for converting dates and times to strings.

Have a routine that takes a buffer, a strftime format, and a struct tm *
as arguments, and:

* checks whether the struct tm * is null and, if so, returns a string
indicating that the date and time couldn't be converted;

* otherwise, passes it to strftime(), along with the buffer and the
format argument and, if strftime() returns 0, meaning the string didn't
fit into the buffer and thus that the buffer's contents are undefined,
returns a string indicating that the date and time didn't fit into the
buffer;

* otherwise, returns a pointer to the buffer.

Call that routine instead of directly calling strftime() in printers;
that prevents printing a buffer with undefined data if the buffer isn't
big enough for the string.

Also, when generating file names using an strftime format, check the
return value of strftime() to make sure the buffer didn't overflow.

9 files changed, 77 insertions, 61 deletions

diff --git a/netdissect.h b/netdissect.h
index 5c16be66..b1074ef7 100644
--- a/netdissect.h
+++ b/netdissect.h
@@ -423,6 +423,9 @@ extern void ts_print(netdissect_options *, const struct timeval *);
 extern void signed_relts_print(netdissect_options *, int32_t);
 extern void unsigned_relts_print(netdissect_options *, uint32_t);
 
+extern const char *nd_format_time(char *buf, size_t bufsize,
+    const char *format, const struct tm *timeptr);
+
 extern void fn_print_char(netdissect_options *, u_char);
 extern void fn_print_str(netdissect_options *, const u_char *);
 extern u_int nd_printztn(netdissect_options *, const u_char *, u_int, const u_char *);
diff --git a/ntp.c b/ntp.c
index 10fabe4b..ec8f659a 100644
--- a/ntp.c
+++ b/ntp.c
@@ -54,8 +54,8 @@ p_ntp_time(netdissect_options *ndo,
 	if (i) {
 	    int64_t seconds_64bit = (int64_t)i - JAN_1970;
 	    time_t seconds;
-	    struct tm *tm;
 	    char time_buf[128];
+	    const char *time_string;
 
 	    seconds = (time_t)seconds_64bit;
 	    if (seconds != seconds_64bit) {
@@ -63,21 +63,12 @@ p_ntp_time(netdissect_options *ndo,
 		 * It doesn't fit into a time_t, so we can't hand it
 		 * to gmtime.
 		 */
-		ND_PRINT(" (unrepresentable)");
+		time_string = "[Time is too large to fit into a time_t]";
 	    } else {
-		tm = gmtime(&seconds);
-		if (tm == NULL) {
-		    /*
-		     * gmtime() can't handle it.
-		     * (Yes, that might happen with some version of
-		     * Microsoft's C library.)
-		     */
-		    ND_PRINT(" (unrepresentable)");
-		} else {
-		    /* use ISO 8601 (RFC3339) format */
-		    strftime(time_buf, sizeof (time_buf), "%Y-%m-%dT%H:%M:%SZ", tm);
-		    ND_PRINT(" (%s)", time_buf);
-		}
+		/* use ISO 8601 (RFC3339) format */
+		time_string = nd_format_time(time_buf, sizeof (time_buf),
+		  "%Y-%m-%dT%H:%M:%SZ", gmtime(&seconds));
 	    }
+	    ND_PRINT(" (%s)", time_string);
 	}
 }
diff --git a/print-ahcp.c b/print-ahcp.c
index 9859f760..d57edda9 100644
--- a/print-ahcp.c
+++ b/print-ahcp.c
@@ -102,18 +102,14 @@ ahcp_time_print(netdissect_options *ndo,
                 const u_char *cp, uint8_t len)
 {
 	time_t t;
-	struct tm *tm;
-	char buf[BUFSIZE];
+	char buf[sizeof("-yyyyyyyyyy-mm-dd hh:mm:ss UTC")];
 
 	if (len != 4)
 		goto invalid;
 	t = GET_BE_U_4(cp);
-	if (NULL == (tm = gmtime(&t)))
-		ND_PRINT(": gmtime() error");
-	else if (0 == strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", tm))
-		ND_PRINT(": strftime() error");
-	else
-		ND_PRINT(": %s UTC", buf);
+	ND_PRINT(": %s",
+	    nd_format_time(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S UTC",
+	      gmtime(&t)));
 	return;
 
 invalid:
diff --git a/print-arista.c b/print-arista.c
index 039a1ffd..079ad684 100644
--- a/print-arista.c
+++ b/print-arista.c
@@ -10,7 +10,6 @@
 
 #include "netdissect.h"
 #include "extract.h"
-#include "addrtoname.h"
 
 /*
 
@@ -93,17 +92,13 @@ arista_print_date_hms_time(netdissect_options *ndo, uint32_t seconds,
 		uint32_t nanoseconds)
 {
 	time_t ts;
-	struct tm *tm;
-	char buf[BUFSIZE];
+	char buf[sizeof("-yyyyyyyyyy-mm-dd hh:mm:ss")];
 
 	ts = seconds + (nanoseconds / 1000000000);
 	nanoseconds %= 1000000000;
-	if (NULL == (tm = gmtime(&ts)))
-		ND_PRINT("gmtime() error");
-	else if (0 == strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S", tm))
-		ND_PRINT("strftime() error");
-	else
-		ND_PRINT("%s.%09u", buf, nanoseconds);
+	ND_PRINT("%s.%09u",
+	    nd_format_time(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S",
+	       gmtime(&ts)), nanoseconds);
 }
 
 int
diff --git a/print-rx.c b/print-rx.c
index 26b51c19..0a1a8d12 100644
--- a/print-rx.c
+++ b/print-rx.c
@@ -794,12 +794,12 @@ rx_cache_find(netdissect_options *ndo, const struct rx_header *rxh,
 			ND_PRINT(" %" PRIu64, _i); \
 		}
 
-#define DATEOUT() { time_t _t; struct tm *tm; char str[256]; \
+#define DATEOUT() { time_t _t; char str[256]; \
 			_t = (time_t) GET_BE_S_4(bp); \
 			bp += sizeof(int32_t); \
-			tm = localtime(&_t); \
-			strftime(str, 256, "%Y/%m/%d %H:%M:%S", tm); \
-			ND_PRINT(" %s", str); \
+			ND_PRINT(" %s", \
+			    nd_format_time(str, sizeof(str), \
+			      "%Y/%m/%d %H:%M:%S", localtime(&_t))); \
 		}
 
 #define STOREATTROUT() { uint32_t mask, _i; \
diff --git a/print-zep.c b/print-zep.c
index 8119a19e..52901e78 100644
--- a/print-zep.c
+++ b/print-zep.c
@@ -82,12 +82,11 @@ static void zep_print_ts(netdissect_options *ndo, const u_char *p)
 	 */
 	if (i) {
 		time_t seconds = i - JAN_1970;
-		struct tm *tm;
 		char time_buf[128];
 
-		tm = localtime(&seconds);
-		strftime(time_buf, sizeof (time_buf), "%Y/%m/%d %H:%M:%S", tm);
-		ND_PRINT(" (%s)", time_buf);
+		ND_PRINT(" (%s)",
+		    nd_format_time(time_buf, sizeof (time_buf), "%Y/%m/%d %H:%M:%S",
+		      localtime(&seconds)));
 	}
 }
 
diff --git a/smbutil.c b/smbutil.c
index 9e19909a..97217a8d 100644
--- a/smbutil.c
+++ b/smbutil.c
@@ -768,9 +768,8 @@ smb_fdata1(netdissect_options *ndo,
 	case 'T':
 	  {
 	    time_t t;
-	    struct tm *lt;
 	    const char *tstring;
-	    char buffer[sizeof("Www Mmm dd hh:mm:ss yyyyy\n")];
+	    char buffer[sizeof("Www Mmm dd hh:mm:ss yyyyy")];
 	    uint32_t x;
 
 	    switch (atoi(fmt + 1)) {
@@ -800,16 +799,11 @@ smb_fdata1(netdissect_options *ndo,
 		break;
 	    }
 	    if (t != 0) {
-		lt = localtime(&t);
-		if (lt != NULL) {
-		    strftime(buffer, sizeof(buffer), "%a %b %e %T %Y%n", lt);
-		    tstring = buffer;
-		}
-		else
-		    tstring = "(Can't convert time)\n";
+		    tstring = nd_format_time(buffer, sizeof(buffer), "%a %b %e %T %Y",
+		    localtime(&t));
 	    } else
-		tstring = "NULL\n";
-	    ND_PRINT("%s", tstring);
+		tstring = "NULL";
+	    ND_PRINT("%s\n", tstring);
 	    fmt++;
 	    while (ND_ASCII_ISDIGIT(*fmt))
 		fmt++;
diff --git a/tcpdump.c b/tcpdump.c
index 78d0871a..0b654158 100644
--- a/tcpdump.c
+++ b/tcpdump.c
@@ -843,6 +843,8 @@ MakeFilename(char *buffer, char *orig_name, int cnt, int max_chars)
         char *filename = malloc(PATH_MAX + 1);
         if (filename == NULL)
             error("%s: malloc", __func__);
+        if (strlen(orig_name) == 0)
+            error("an empty string is not a valid file name");
 
         /* Process with strftime if Gflag is set. */
         if (Gflag != 0) {
@@ -854,9 +856,25 @@ MakeFilename(char *buffer, char *orig_name, int cnt, int max_chars)
           }
 
           /* There's no good way to detect an error in strftime since a return
-           * value of 0 isn't necessarily failure.
+           * value of 0 isn't necessarily failure; if orig_name is an empty
+           * string, the formatted string will be empty.
+           *
+           * However, the C90 standard says that, if there *is* a
+           * buffer overflow, the content of the buffer is undefined,
+           * so we must check for a buffer overflow.
+           *
+           * So we check above for an empty orig_name, and only call
+           * strftime() if it's non-empty, in which case the return
+           * value will only be 0 if the formatted date doesn't fit
+           * in the buffer.
+           *
+           * (We check above because, even if we don't use -G, we
+           * want a better error message than "tcpdump: : No such
+           * file or directory" for this case.)
            */
-          strftime(filename, PATH_MAX, orig_name, local_tm);
+          if (strftime(filename, PATH_MAX, orig_name, local_tm) == 0) {
+            error("%s: strftime", __func__);
+          }
         } else {
           strncpy(filename, orig_name, PATH_MAX);
         }
diff --git a/util-print.c b/util-print.c
index 8b206497..05483378 100644
--- a/util-print.c
+++ b/util-print.c
@@ -230,7 +230,8 @@ ts_date_hmsfrac_print(netdissect_options *ndo, long sec, long usec,
 {
 	time_t Time = sec;
 	struct tm *tm;
-	char timestr[32];
+	char timebuf[32];
+	const char *timestr;
 
 	if ((unsigned)sec & 0x80000000) {
 		ND_PRINT("[Error converting time]");
@@ -242,14 +243,13 @@ ts_date_hmsfrac_print(netdissect_options *ndo, long sec, long usec,
 	else
 		tm = gmtime(&Time);
 
-	if (!tm) {
-		ND_PRINT("[Error converting time]");
-		return;
+	if (date_flag == WITH_DATE) {
+		timestr = nd_format_time(timebuf, sizeof(timebuf),
+		    "%Y-%m-%d %H:%M:%S", tm);
+	} else {
+		timestr = nd_format_time(timebuf, sizeof(timebuf),
+		    "%H:%M:%S", tm);
 	}
-	if (date_flag == WITH_DATE)
-		strftime(timestr, sizeof(timestr), "%Y-%m-%d %H:%M:%S", tm);
-	else
-		strftime(timestr, sizeof(timestr), "%H:%M:%S", tm);
 	ND_PRINT("%s", timestr);
 
 	ts_frac_print(ndo, usec);
@@ -405,6 +405,26 @@ signed_relts_print(netdissect_options *ndo,
 	unsigned_relts_print(ndo, secs);
 }
 
+/*
+ * Format a struct tm with strftime().
+ * If the pointer to the struct tm is null, that means that the
+ * routine to convert a time_t to a struct tm failed; the localtime()
+ * and gmtime() in the Microsoft Visual Studio C library will fail,
+ * returning null, if the value is before the UNIX Epoch.
+ */
+const char *
+nd_format_time(char *buf, size_t bufsize, const char *format,
+         const struct tm *timeptr)
+{
+	if (timeptr != NULL) {
+		if (strftime(buf, bufsize, format, timeptr) != 0)
+			return (buf);
+		else
+			return ("[nd_format_time() buffer is too small]");
+	} else
+		return ("[localtime() or gmtime() couldn't convert the date and time]");
+}
+
 /* Print the truncated string */
 void nd_print_trunc(netdissect_options *ndo)
 {