This patch was submitted upstream by Jens Elkner, who reported it on #pkg5;

it was accepted after the 5.3.1 release.

--- zsh-5.0.7/Src/watch.c.orig	Thu Jul 31 20:41:49 2014

+++ zsh-5.0.7/Src/watch.c	Wed Jan 11 16:37:49 2017

@@ -87,6 +87,9 @@

 #if !defined(WATCH_STRUCT_UTMP) && defined(HAVE_STRUCT_UTMPX) && defined(REAL_UTMPX_FILE)

 # define WATCH_STRUCT_UTMP struct utmpx

+# define setutent setutxent

+# define getutent getutxent

+# define endutent endutxent 

 /*

  * In utmpx, the ut_name field is replaced by ut_user.

  * Howver, on some systems ut_name may already be defined this

@@ -141,9 +144,9 @@

 #  define WATCH_WTMP_FILE "/dev/null"

 # endif

-static int wtabsz;

-static WATCH_STRUCT_UTMP *wtab;

-static time_t lastutmpcheck;

+static int wtabsz = 0;

+static WATCH_STRUCT_UTMP *wtab = NULL;

+static time_t lastutmpcheck = 0;

 /* get the time of login/logout for WATCH */

@@ -449,34 +452,44 @@

 /* initialize the user List */

 /**/

-static void

-readwtab(void)

+static int

+readwtab(WATCH_STRUCT_UTMP **head, int initial_sz)

 {

-    WATCH_STRUCT_UTMP *uptr;

-    int wtabmax = 32;

-    FILE *in;

+    WATCH_STRUCT_UTMP *uptr, *tmp;

+    int wtabmax = initial_sz < 2 ? 32 : initial_sz;

+    int sz = 0;

-    wtabsz = 0;

-    if (!(in = fopen(WATCH_UTMP_FILE, "r")))

-	return;

-    uptr = wtab = (WATCH_STRUCT_UTMP *)zalloc(wtabmax * sizeof(WATCH_STRUCT_UTMP));

-    while (fread(uptr, sizeof(WATCH_STRUCT_UTMP), 1, in))

+

+    uptr = *head = (WATCH_STRUCT_UTMP *)zalloc(wtabmax * sizeof(WATCH_STRUCT_UTMP));

+	setutent();

+    while ((tmp = getutent()) != NULL)

 # ifdef USER_PROCESS

-	if   (uptr->ut_type == USER_PROCESS)

+	if   (tmp->ut_type == USER_PROCESS)

 # else /* !USER_PROCESS */

-	if   (uptr->ut_name[0])

+	if   (tmp->ut_name[0])

 # endif /* !USER_PROCESS */

 	{

+		memcpy(uptr, tmp, sizeof (WATCH_STRUCT_UTMP));

 	    uptr++;

-	    if (++wtabsz == wtabmax)

-		uptr = (wtab = (WATCH_STRUCT_UTMP *)realloc((void *) wtab, (wtabmax *= 2) *

-						      sizeof(WATCH_STRUCT_UTMP))) + wtabsz;

+	    if (++sz == wtabmax) {

+			uptr = (WATCH_STRUCT_UTMP *)

+				realloc(*head, (wtabmax *= 2) * sizeof(WATCH_STRUCT_UTMP));

+			if (uptr == NULL) {

+				/* memory pressure - so stop consuming and use, what we have

+				 * Other option is to exit() here, as zmalloc does on error */

+				sz--;

+				break;

+			}

+			*head = uptr;

+			uptr += sz;

+		}

 	}

-    fclose(in);

+    endutent();

-    if (wtabsz)

-	qsort((void *) wtab, wtabsz, sizeof(WATCH_STRUCT_UTMP),

+    if (sz)

+	qsort((void *) *head, sz, sizeof(WATCH_STRUCT_UTMP),

 	           (int (*) _((const void *, const void *)))ucmp);

+	return sz;

 }

 /* Check for login/logout events; executed before *

@@ -486,55 +499,28 @@

 void

 dowatch(void)

 {

-    FILE *in;

     WATCH_STRUCT_UTMP *utab, *uptr, *wptr;

     struct stat st;

     char **s;

     char *fmt;

-    int utabsz = 0, utabmax = wtabsz + 4;

-    int uct, wct;

+    int utabsz, uct, wct;

     s = watch;

     holdintr();

-    if (!wtab) {

-	readwtab();

-	noholdintr();

-	return;

-    }

+    if (!wtab)

+	wtabsz = readwtab(&wtab, 32);

     if ((stat(WATCH_UTMP_FILE, &st) == -1) || (st.st_mtime <= lastutmpcheck)) {

 	noholdintr();

 	return;

     }

     lastutmpcheck = st.st_mtime;

-    uptr = utab = (WATCH_STRUCT_UTMP *) zalloc(utabmax * sizeof(WATCH_STRUCT_UTMP));

-

-    if (!(in = fopen(WATCH_UTMP_FILE, "r"))) {

-	free(utab);

-	noholdintr();

-	return;

-    }

-    while (fread(uptr, sizeof *uptr, 1, in))

-# ifdef USER_PROCESS

-	if (uptr->ut_type == USER_PROCESS)

-# else /* !USER_PROCESS */

-	if (uptr->ut_name[0])

-# endif /* !USER_PROCESS */

-	{

-	    uptr++;

-	    if (++utabsz == utabmax)

-		uptr = (utab = (WATCH_STRUCT_UTMP *)realloc((void *) utab, (utabmax *= 2) *

-						      sizeof(WATCH_STRUCT_UTMP))) + utabsz;

-	}

-    fclose(in);

+    utabsz = readwtab(&utab, wtabsz + 4);

     noholdintr();

     if (errflag) {

 	free(utab);

 	return;

     }

-    if (utabsz)

-	qsort((void *) utab, utabsz, sizeof(WATCH_STRUCT_UTMP),

-	           (int (*) _((const void *, const void *)))ucmp);

     wct = wtabsz;

     uct = utabsz;