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

From: Neil Horman
Date: Fri Jun 26 2009 - 14:02:39 EST



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@xxxxxxxxxxxxx>
Reported-by: Earl Chew <earl_chew@xxxxxxxxxxx>


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;
}

+ helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc);
+
core_limit = RLIM_INFINITY;

/* SIGPIPE can happen, but it's just never processed */
--
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