Re: [PATCH 1/3] exec: Make do_coredump more resilient to recursive crashes (v5)

Neil Horman
2009-07-01T15:30:35Z

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;