On Fri, Sep 11, 2020 at 1:49 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > On Thu, Sep 10, 2020 at 01:21:06PM -0700, Kees Cook wrote: > > From: John Wood <john.wood@xxxxxxx> > > > > To detect a fork brute force attack it is necessary to compute the > > crashing rate of the application. This calculation is performed in each > > fatal fail of a task, or in other words, when a core dump is triggered. > > If this rate shows that the application is crashing quickly, there is a > > clear signal that an attack is happening. > > > > Since the crashing rate is computed in milliseconds per fault, if this > > rate goes under a certain threshold a warning is triggered. > > > > Signed-off-by: John Wood <john.wood@xxxxxxx> > > --- > > fs/coredump.c | 2 ++ > > include/fbfam/fbfam.h | 2 ++ > > security/fbfam/fbfam.c | 39 +++++++++++++++++++++++++++++++++++++++ > > 3 files changed, 43 insertions(+) > > > > 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. > 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.
