Date: Fri, 15 May 2009 09:02:39 +0200 From: Ed Schouten <ed@80386.nl> To: Konstantin Belousov <kib@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r192094 - head/sys/kern Message-ID: <20090515070239.GQ58540@hoeg.nl> In-Reply-To: <200905141054.n4EAsvp1088977@svn.freebsd.org> References: <200905141054.n4EAsvp1088977@svn.freebsd.org>
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Hi Kostik,
* Konstantin Belousov <kib@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.
--
Ed Schouten <ed@80386.nl>
WWW: http://80386.nl/
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