We're working on a user space control plane for the BPF sk_lookup hook [1]. The hook attaches to a network namespace and allows control over which socket receives a new connection / packet.
Roughly, applications can give a socket to our user space component to participate in custom bind semantics. This creates an edge case where an application can provide us with a socket that lives in a different network namespace than our BPF sk_lookup program. We'd like to return an error in this case.
Additionally, we have some user space state that is tied to the network namespace. We currently use the inode of the nsfs entry in a directory name, but this is suffers from inode reuse.
I'm proposing to fix both of these issues by adding a new SO_NETNS_COOKIE socket option as well as a NS_GET_COOKIE ioctl. Using these we get a stable, unique identifier for a network namespace and check whether a socket belongs to the "correct" namespace.
NS_GET_COOKIE could be renamed to NS_GET_NET_COOKIE. I kept the name generic because it seems like other namespace types could benefit from a cookie as well.
I'm trying to land this via the bpf tree since this is where the netns cookie originated, please let me know if this isn't appropriate.
1: https://www.kernel.org/doc/html/latest/bpf/prog_sk_lookup.html
Cc: bpf@vger.kernel.org Cc: linux-alpha@vger.kernel.org Cc: linux-api@vger.kernel.org Cc: linux-arch@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Cc: linux-mips@vger.kernel.org Cc: linux-parisc@vger.kernel.org Cc: netdev@vger.kernel.org Cc: sparclinux@vger.kernel.org
Lorenz Bauer (4): net: add SO_NETNS_COOKIE socket option nsfs: add an ioctl to discover the network namespace cookie tools/testing: add test for NS_GET_COOKIE tools/testing: add a selftest for SO_NETNS_COOKIE
arch/alpha/include/uapi/asm/socket.h | 2 + arch/mips/include/uapi/asm/socket.h | 2 + arch/parisc/include/uapi/asm/socket.h | 2 + arch/sparc/include/uapi/asm/socket.h | 2 + fs/nsfs.c | 9 +++ include/linux/sock_diag.h | 20 ++++++ include/net/net_namespace.h | 11 ++++ include/uapi/asm-generic/socket.h | 2 + include/uapi/linux/nsfs.h | 2 + net/core/filter.c | 9 ++- net/core/sock.c | 7 +++ tools/testing/selftests/net/.gitignore | 1 + tools/testing/selftests/net/Makefile | 2 +- tools/testing/selftests/net/so_netns_cookie.c | 61 +++++++++++++++++++ tools/testing/selftests/nsfs/.gitignore | 1 + tools/testing/selftests/nsfs/Makefile | 2 +- tools/testing/selftests/nsfs/netns.c | 57 +++++++++++++++++ 17 files changed, 185 insertions(+), 7 deletions(-) create mode 100644 tools/testing/selftests/net/so_netns_cookie.c create mode 100644 tools/testing/selftests/nsfs/netns.c