exec: make do_coredump() more resilient to recursive crashes

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.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Reported-by: Earl Chew <earl_chew@agilent.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 22 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 5c833c18d0d4..735d9c18ec71 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1799,38 +1799,39 @@ 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) && (core_limit < binfmt->min_coredump))
                 goto fail_unlock;
 
         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;