Re: [PATCH 1/3] exec: Make do_coredump more resilient to recursive crashes (v8)

Neil Horman
2009-07-07T16:14:23Z

Reposting with Oleg CC'd for him to ACK

On Fri, Jul 03, 2009 at 06:50:08AM -0400, Neil Horman 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.
>
> Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
> Reported-by: Earl Chew <earl_chew@agilent.com>
>
>
> exec.c | 43 +++++++++++++++++++++----------------------
> 1 file changed, 21 insertions(+), 22 deletions(-)
>
> diff --git a/fs/exec.c b/fs/exec.c
> index 9e05bd8..9defd20 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1776,35 +1776,34 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs)
> lock_kernel();
> ispipe = format_corename(corename, signr);
> unlock_kernel();
> - /*
> - * Don't bother to check the RLIMIT_CORE value if core_pattern points
> - * to a pipe. Since we're not writing directly to the filesystem
> - * RLIMIT_CORE doesn't really apply, as no actual core file will be
> - * created unless the pipe reader choses to write out the core file
> - * at which point file size limits and permissions will be imposed
> - * as it does with any other process
> - */
> +
> if (ispipe) {
> + 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;
> + }
> +
> helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc);
> if (!helper_argv) {
> printk(KERN_WARNING "%s failed to allocate memory\n",
> __func__);
> goto fail_unlock;
> }
> - /* 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");
> - goto fail_unlock;
> - }
>
> core_limit = RLIM_INFINITY;
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
>