On Fri, May 15, 2009 at 09:02:39AM +0200, Ed Schouten wrote:
> Hi Kostik,
>
> * Konstantin Belousov <k...@freebsd.org> wrote:
> > Log:
> > Do not advance req->oldidx when sysctl_old_user returning an
> > error due to copyout failure or short buffer.
> >
> > The later breaks the usermode iterators of the sysctl results that pack
> > arbitrary number of variable-sized structures. Iterator expects that
> > kernel filled exactly oldlen bytes, and tries to interpret half-filled
> > or garbage structure at the end of the buffer. In particular,
> > kinfo_getfile(3) segfaulted.
> >
> > Reported and tested by: pho
> > MFC after: 3 weeks
>
> Is it possible that this change introduces a regression? Right now
> `pstat -t' gets stuck in an infinite loop. I've added the following
> printf:
>
> | Index: pstat.c
> | ===================================================================
> | --- pstat.c (revision 192128)
> | +++ pstat.c (working copy)
> | @@ -263,6 +263,7 @@
> | if (errno != ENOMEM)
> | err(1, "sysctlbyname()");
> | len *= 2;
> | + printf("Going to %zu\n", len);
> | if ((xttys = realloc(xttys, len)) == NULL)
> | err(1, "realloc()");
> | }
>
> pstat on -CURRENT prints:
>
> | LINE INQ CAN LIN LOW OUTQ USE LOW COL SESS PGID STATE
> | Going to 0
> | Going to 0
> | Going to 0
> | ...
>
> If I use the same patch on RELENG_6, I get the expected result:
>
> | LINE RAW CAN OUT IHIWT ILOWT OHWT LWT COL STATE SESS PGID
> DISC
> | Going to 272
> | Going to 544
> | Going to 1088
> | Going to 2176
> | Going to 4352
> | Going to 8704
> | sysmouse 0 0 0 0 0 0 0 0 - 0 0
> term
> | ...
>
> So the problem is that sysctl overwrites the len argument with 0, even
> if it returns back to userspace with ENOMEM.
>
> I see we have two changes in sysctl. In theory it could also be related
> to jhb@'s changes to sysctl locking, but I suspect it's less likely.
>
I can confirm that it is r192094 that triggers the loop.
- Peter
> --
> Ed Schouten <e...@80386.nl>
> WWW: http://80386.nl/
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