On Fri, Sep 11, 2015 at 03:02:36PM +0200, Daniel Borkmann wrote: > On 09/11/2015 02:20 AM, Tycho Andersen wrote: > >In the next patch, we're going to add a way to access the underlying > >filters via bpf fds. This means that we need to ref-count both the > >struct seccomp_filter objects and the struct bpf_prog objects separately, > >in case a process dies but a filter is still referred to by another > >process. > > > >Additionally, we mark classic converted seccomp filters as seccomp eBPF > >programs, since they are a subset of what is supported in seccomp eBPF. > > > >Signed-off-by: Tycho Andersen <tycho.andersen@xxxxxxxxxxxxx> > >CC: Kees Cook <keescook@xxxxxxxxxxxx> > >CC: Will Drewry <wad@xxxxxxxxxxxx> > >CC: Oleg Nesterov <oleg@xxxxxxxxxx> > >CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > >CC: Pavel Emelyanov <xemul@xxxxxxxxxxxxx> > >CC: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx> > >CC: Alexei Starovoitov <ast@xxxxxxxxxx> > >CC: Daniel Borkmann <daniel@xxxxxxxxxxxxx> > >--- > > kernel/seccomp.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > >diff --git a/kernel/seccomp.c b/kernel/seccomp.c > >index 245df6b..afaeddf 100644 > >--- a/kernel/seccomp.c > >+++ b/kernel/seccomp.c > >@@ -378,6 +378,8 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog) > > } > > > > atomic_set(&sfilter->usage, 1); > >+ atomic_set(&sfilter->prog->aux->refcnt, 1); > >+ sfilter->prog->type = BPF_PROG_TYPE_SECCOMP; > > So, if you do this, then this breaks the assumption of eBPF JITs > that, currently, all classic converted BPF programs always have a > prog->type of BPF_PROG_TYPE_UNSPEC (see: bpf_prog_was_classic()). > > Currently, JITs make use of this information to determine whether > A and X mappings for such programs should or should not be cleared > in the prologue (s390 currently). > > In the seccomp_prepare_filter() stage, we're already past that, so > it will not cause an issue, but we certainly would need to be very > careful in future, if bpf_prog_was_classic() is then used at a later > stage when we already have a generated bpf_prog somewhere, as then > this assumption will break. The only reason we need to do this is to allow BPF_DUMP_PROG to work, since we were restricting it to only allow dumping of seccomp programs, since those don't have maps. Instead, perhaps we could allow dumping of BPF_PROG_TYPE_SECCOMP and BPF_PROG_TYPE_UNSPEC? Tycho -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
