On 09/11/2015 04:44 PM, Tycho Andersen wrote:
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?
There are possibilities that BPF_PROG_TYPE_UNSPEC is calling helpers
already today, at least in networking case, not seccomp. So, since
you want to export [classic -> eBPF] only for seccomp, put fds on them
and dump these via bpf(2), you could allow that (with a big comment
stating why it's safe), but mid-term we really need to sanitize all
this stuff properly as this is needed for other types, too.
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