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

    >
    >
    > 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

    /*
    *
    *

    - 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;


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