check return from pread, don't divide -1 for count

diff --git a/libexec/comsat/comsat.c b/libexec/comsat/comsat.c
index ef9a0b4..df7283b 100644 (file)
--- a/libexec/comsat/comsat.c
+++ b/libexec/comsat/comsat.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: comsat.c,v 1.47 2017/04/03 17:07:58 deraadt Exp $     */
+/*     $OpenBSD: comsat.c,v 1.48 2017/04/03 17:23:39 tedu Exp $        */
 
 /*
  * Copyright (c) 1980, 1993
@@ -170,6 +170,7 @@ doreadutmp(void)
        static u_int utmpsize;          /* last malloced size for utmp */
        static time_t utmpmtime;        /* last modification time for utmp */
        struct stat statbf;
+       int n;
 
        if (time(NULL) - lastmsgtime >= MAXIDLE)
                exit(0);
@@ -195,7 +196,10 @@ doreadutmp(void)
                        utmp = u;
                        utmpsize = nutmpsize;
                }
-               nutmp = pread(uf, utmp, statbf.st_size, 0)/sizeof(struct utmp);
+               n = pread(uf, utmp, statbf.st_size, 0);
+               if (n == -1)
+                       n = 0;
+               nutmp = n / sizeof(struct utmp);
                dsyslog(LOG_DEBUG, "read %d utmp entries", nutmp);
        }
        (void)alarm(15);