Re: [PATCH 1/2] exec: Make do_coredump more robust and safer when using pipes in core_pattern: recursive dump detection

Neil Horman
2009-06-26T20:18:16Z

On Fri, Jun 26, 2009 at 12:37:23PM -0700, Andrew Morton wrote:
> On Fri, 26 Jun 2009 14:02:22 -0400
> Neil Horman <nhorman@tuxdriver.com> wrote:
>
> >
> > core_pattern: Change how we detect recursive dumps with core_pattern pipes
> >
> > Change how we detect recursive dumps. Currently we have a mechanism by which
> > we try to compare pathnames of the crashing process to the core_pattern path.
> > This is broken for a dozen reasons, and just doesn't work in any sort of robust
> > way. I'm replacing it with the use of a 0 RLIMIT_CORE value. Since helper
> > apps set RLIMIT_CORE to zero, we don't write out core files for any process with
> > that particular limit set. It the core_pattern is a pipe, any non-zero limit is
> > translated to RLIM_INFINITY. This allows complete dumps to be captured, but
> > prevents infinite recursion in the event that the core_pattern process itself
> > crashes.
> >
>
> The patch appears to be against 2.6.30 or something. I get rejects due
> to some other patch in exec.c which was added three weeks ago. Please
> don't do that :(
>

No, this patch is against a branch I made from the 2.6.28-rc2 tag, to which I
cleanly applied your -mm patch that I got from kernel.org.

> >
> >
> > exec.c | 32 +++++++++++++++++++-------------
> > 1 file changed, 19 insertions(+), 13 deletions(-)
> >
> > diff --git a/fs/exec.c b/fs/exec.c
> > index ebe359f..163cfa7 100644
> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -1802,22 +1802,28 @@ int do_coredump(long signr, int exit_code, struct pt_regs * regs)
> > goto fail_unlock;
> >
> > if (ispipe) {
> > - helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc);
> > - /* Terminate the string before the first option */
> > - delimit = strchr(corename, ' ');
> > - if (delimit)
> > - *delimit = '\0';
> > - delimit = strrchr(helper_argv[0], '/');
> > - if (delimit)
> > - delimit++;
> > - else
> > - delimit = helper_argv[0];
> > - if (!strcmp(delimit, current->comm)) {
> > - printk(KERN_NOTICE "Recursive core dump detected, "
> > - "aborting\n");
> > + if (core_limit == 0) {
> > + /*
> > + * Normally core limits are irrelevant to pipes, since
> > + * we're not writing to the file system, but we use
> > + * core_limit of 0 here as a speacial value. Any
> > + * non-zero limit gets set to RLIM_INFINITY below, but
> > + * a limit of 0 skips the dump. This is a consistent
> > + * way to catch recursive crashes. We can still crash
> > + * if the core_pattern binary sets RLIM_CORE = !0
> > + * but it runs as root, and can do lots of stupid things
> > + * Note that we use task_tgid_vnr here to grab the pid of the
> > + * process group leader. That way we get the right pid if a thread
> > + * in a multi-threaded core_pattern process dies.
> > + */
> > + printk(KERN_WARNING "Process %d(%s) has RLIMIT_CORE set to 0\n",
> > + task_tgid_vnr(current), current->comm);
> > + printk(KERN_WARNING "Aborting core\n");
> > goto fail_unlock;
> > }
>
> A few cosmetic things:
>
> - The asterisks don't line up in the comment block. Normally we'll do
>
> /*
> *
> *
>
> rather than
>
> /*
> *
> *
>
I'll fix that

> - The comment overflows 80 columns and makes a mess.
>
> - Would it not be neater to do this check in a separate function?
> Then the comment block can go above the function rather than being
> all scrunched to the right and do_coredump() (which is already >150
> lines) just gets
>
> if (ispipe) {
> + if (core_limit_is_zero())
> + goto fail_unlock;
Yeah, I can do that.
Neil

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