RE: SIGSEGV, Segmentation fault.

[Jan-Henrik Haukeland]

I'm not sure and I may be wrong, but from the top of my head I do not think
this is a buffer-size problem i.e. it's not necessary to add 1 byte to the
buffer when snprintf is used. The buffer is not going to get overrun and
snprintf adds a '\0' char at the end of the buffer. The man page for *printf
says:

   sprintf  stores the output in the specified char array str
   and snprintf limits number of characters written to str to
   at  most  size (including terminating 0)...

And as you can see in the strange string Igor got when he ran gdb,  the NUL
char was added, the rest of the garble is normal (probably) since the string
was uninitialized. It seems that the problem is vsnprintf and it fails (with
malloc!?) because it has problems with the format string? Again from the man
page:

  For sprintf and snprintf, the behavior is also  undefined  if  the  output
  *<[str>>  overlaps with one of the arguments.

Undefined behaviour usually means SIGSEGV :-) So my two cents are on the
vsnprintf statement and on the format argument. (I'm on windows right now and
helping my brother building a house in another town so I cannot check the patch
right now, but I'll be back next week).

Cheers!

Jan-Henrik

> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden
> Behalf Of Martin Pala
> Sent: 20. mai 2003 21:45
> To: This is the general mailing list for monit
> Subject: Re: SIGSEGV, Segmentation fault.
>
>
> This kind of error (i think it was the cause of problem) was in the
> sources more then once - new patch which should generaly fix it
> attached, please try it, Igor.
>
> Thanks,
> Martin
>
> Martin wrote:
>
> >Hi Igor,
> >
> >can you try attached patch?
> >
> >Thanks,
> >
> >Cheers,
> >Martin
> >
> >----- Původní zpráva -----
> >Od: Igor Homyakov <address@hidden>
> >Datum: úterý, 20. května 2003 v 9:32 dop.
> >Předmět: SIGSEGV, Segmentation fault.
> >
> >
> >
> >>address@hidden monit-3.2]# gdb ./monit
> >>GNU gdb ALT Linux (5.2.1-alt2)
> >>Copyright 2002 Free Software Foundation, Inc.
> >>GDB is free software, covered by the GNU
> >>General Public License, and you are
> >>welcome to change it and/or distribute copies
> >>of it under certain conditions.
> >>Type "show copying" to see the conditions.
> >>There is absolutely no warranty for GDB.
> >>Type "show warranty" for details.
> >>This GDB was configured as "i586-alt-linux"...
> >>(gdb) break do_default
> >>Breakpoint 1 at 0x804f09c: file monitor.c,
> >>line 496.
> >>(gdb) run
> >>Starting program:
> >>/home/homyakov/RPM/BUILD/monit-3.2/monit
> >>[New Thread 1024 (LWP 14649)]
> >>[Switching to Thread 1024 (LWP 14649)]
> >>
> >>Breakpoint 1, do_default () at monitor.c:496
> >>496       if(Run.isdaemon) {
> >>(gdb) n
> >>498         if(do_wakeupcall()) {
> >>(gdb) n
> >>504         log("Starting %s daemon\n", prog);
> >>(gdb) s
> >>log (format=0x80619e0 "Starting %s daemon\n")
> >>at log.c:116
> >>116       ASSERT(format);
> >>(gdb) s
> >>118       va_start(ap,format);
> >>(gdb) n
> >>119       vsnprintf(msg, STRLEN, format, ap);
> >>(gdb) n
> >>122       if(! Run.dolog) goto nolog;
> >>(gdb) n
> >>124       if(Run.use_syslog) {
> >>(gdb) n
> >>126         syslog(LOG_ERR|LOG_USER, "%s", msg);
> >>(gdb) print msg
> >>$1 = "Starting monit
> >>
> >>
> >>
> >daemon\n\0*???\177t?\004\bH5\a\b\220??\177\210??\177;?\004\b/var/run
> /mon\0\0\0\0id\0*???*x??*0??*???*???*\e\0?*?\232?*\220R?*\200N?*???\1
> 77\216??*\235\035?*???*x??*0??*\0\0\0\0???*\0\0\0\00??*0??\177?D?*\e\
> address@hidden(??\177uC\005\bH5\a\b\0\0\0\0(??\177L\214?
> *L\214?*`\234?*"...(gdb)
> >n
> >
> >
> >>
> >>Program received signal SIGSEGV, Segmentation
> >>fault.0x2ac6011a in malloc () from
> >>/lib/libc.so.6(gdb) where
> >>#0  0x2ac6011a in malloc () from /lib/libc.so.6
> >>#1  0x2ac5fc7e in malloc () from /lib/libc.so.6
> >>#2  0x2ac57997 in open_memstream () from
> >>/lib/libc.so.6#3  0x2acb90a9 in vsyslog ()
> >>from /lib/libc.so.6
> >>#4  0x2acb8ebd in syslog () from /lib/libc.so.6
> >>#5  0x0804d4f5 in log (format=0x80619e0
> >>"Starting %s daemon\n") at log.c:126
> >>#6  0x0804f0cf in do_default () at monitor.c:504
> >>#7  0x0804ec5d in do_action (args=0x7ffff8f4)
> >>at monitor.c:316
> >>#8  0x0804e917 in main (argc=1,
> >>argv=0x7ffff8f4) at monitor.c:96
> >>#9  0x2ac0b652 in __libc_start_main () from
> >>/lib/libc.so.6
> >>
> >>--
> >>Igor Homyakov
> >><homyakov AT ramax.spb.ru>
> >>
> >>
> >>--
> >>To unsubscribe:
> >>http://mail.nongnu.org/mailman/listinfo/monit-
> >>general
> >>
>
>