On Fri, Sep 11, 2020 at 02:01:56AM +0200, Jann Horn wrote:

quoted

On Fri, Sep 11, 2020 at 1:49 AM Kees Cook [off-list ref] wrote:

quoted

On Thu, Sep 10, 2020 at 01:21:06PM -0700, Kees Cook wrote:

quoted

diff --git a/fs/coredump.c b/fs/coredump.c
index 76e7c10edfc0..d4ba4e1828d5 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c

@@ -51,6 +51,7 @@
 #include "internal.h"

 #include <trace/events/sched.h>
+#include <fbfam/fbfam.h>

 int core_uses_pid;
 unsigned int core_pipe_limit;

@@ -825,6 +826,7 @@ void do_coredump(const kernel_siginfo_t *siginfo)
 fail_creds:
      put_cred(cred);
 fail:
+     fbfam_handle_attack(siginfo->si_signo);

I don't think this is the right place for detecting a crash -- isn't
this only for the "dumping core" condition? In other words, don't you
want to do this in get_signal()'s "fatal" block? (i.e. very close to the
do_coredump, but without the "should I dump?" check?)

Hmm, but maybe I'm wrong? It looks like you're looking at noticing the
process taking a signal from SIG_KERNEL_COREDUMP_MASK ?

(Better yet: what are fatal conditions that do NOT match
SIG_KERNEL_COREDUMP_MASK, and should those be covered?)

Regardless, *this* looks like the only place without an LSM hook. And it
doesn't seem unreasonable to add one here. I assume it would probably
just take the siginfo pointer, which is also what you're checking.

Good point, making this an LSM might be a good idea.

quoted

e.g. for include/linux/lsm_hook_defs.h:

LSM_HOOK(int, 0, task_coredump, const kernel_siginfo_t *siginfo);

I guess it should probably be an LSM_RET_VOID hook? And since, as you
said, it's not really semantically about core dumping, maybe it should
be named task_fatal_signal or something like that.

If I understand correctly you propose to add a new LSM hook without return
value and place it here:

diff --git a/kernel/signal.c b/kernel/signal.c
index a38b3edc6851..074492d23e98 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c

@@ -2751,6 +2751,8 @@ bool get_signal(struct ksignal *ksig)
                        do_coredump(&ksig->info);
                }

+               // Add the new LSM hook here
+
                /*
                 * Death signals, no core dump.
                 */