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Date: Fri, 31 Mar 2023 19:24:31 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
Cc: willemdebruijn.kernel@...il.com, gnoack3000@...il.com,
linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org, yusongping@...wei.com,
artem.kuzin@...wei.com
Subject: Re: [PATCH v10 09/13] landlock: Add network rules and TCP hooks
support
On 23/03/2023 09:52, Konstantin Meskhidze wrote:
> This commit adds network rules support in the ruleset management
> helpers and the landlock_create_ruleset syscall.
> Refactor user space API to support network actions. Add new network
> access flags, network rule and network attributes. Increment Landlock
> ABI version. Expand access_masks_t to u32 to be sure network access
> rights can be stored. Implement socket_bind() and socket_connect()
> LSM hooks, which enable to restrict TCP socket binding and connection
> to specific ports.
>
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
> ---
>
> Changes since v9:
> * Changes UAPI port field to __u64.
> * Moves shared code into check_socket_access().
> * Adds get_raw_handled_net_accesses() and
> get_current_net_domain() helpers.
> * Minor fixes.
>
> Changes since v8:
> * Squashes commits.
> * Refactors commit message.
> * Changes UAPI port field to __be16.
> * Changes logic of bind/connect hooks with AF_UNSPEC families.
> * Adds address length checking.
> * Minor fixes.
>
> Changes since v7:
> * Squashes commits.
> * Increments ABI version to 4.
> * Refactors commit message.
> * Minor fixes.
>
> Changes since v6:
> * Renames landlock_set_net_access_mask() to landlock_add_net_access_mask()
> because it OR values.
> * Makes landlock_add_net_access_mask() more resilient incorrect values.
> * Refactors landlock_get_net_access_mask().
> * Renames LANDLOCK_MASK_SHIFT_NET to LANDLOCK_SHIFT_ACCESS_NET and use
> LANDLOCK_NUM_ACCESS_FS as value.
> * Updates access_masks_t to u32 to support network access actions.
> * Refactors landlock internal functions to support network actions with
> landlock_key/key_type/id types.
>
> Changes since v5:
> * Gets rid of partial revert from landlock_add_rule
> syscall.
> * Formats code with clang-format-14.
>
> Changes since v4:
> * Refactors landlock_create_ruleset() - splits ruleset and
> masks checks.
> * Refactors landlock_create_ruleset() and landlock mask
> setters/getters to support two rule types.
> * Refactors landlock_add_rule syscall add_rule_path_beneath
> function by factoring out get_ruleset_from_fd() and
> landlock_put_ruleset().
>
> Changes since v3:
> * Splits commit.
> * Adds network rule support for internal landlock functions.
> * Adds set_mask and get_mask for network.
> * Adds rb_root root_net_port.
>
> ---
> include/uapi/linux/landlock.h | 49 +++++
> security/landlock/Kconfig | 1 +
> security/landlock/Makefile | 2 +
> security/landlock/limits.h | 6 +-
> security/landlock/net.c | 198 +++++++++++++++++++
> security/landlock/net.h | 26 +++
> security/landlock/ruleset.c | 52 ++++-
> security/landlock/ruleset.h | 63 +++++-
> security/landlock/setup.c | 2 +
> security/landlock/syscalls.c | 72 ++++++-
> tools/testing/selftests/landlock/base_test.c | 2 +-
> 11 files changed, 450 insertions(+), 23 deletions(-)
> create mode 100644 security/landlock/net.c
> create mode 100644 security/landlock/net.h
[...]
> diff --git a/security/landlock/net.c b/security/landlock/net.c
[...]
> +static int check_addrlen(const struct sockaddr *const address, int addrlen)
const int addrlen
> +{
> + if (addrlen < offsetofend(struct sockaddr, sa_family))
> + return -EINVAL;
> + switch (address->sa_family) {
> + case AF_UNSPEC:
> + case AF_INET:
> + if (addrlen < sizeof(struct sockaddr_in))
> + return -EINVAL;
> + return 0;
> +#if IS_ENABLED(CONFIG_IPV6)
> + case AF_INET6:
> + if (addrlen < SIN6_LEN_RFC2133)
> + return -EINVAL;
> + return 0;
> +#endif
> + }
> + WARN_ON_ONCE(1);
> + return 0;
> +}
> +
> +static u16 get_port(const struct sockaddr *const address)
> +{
> + /* Gets port value in host byte order. */
> + switch (address->sa_family) {
> + case AF_UNSPEC:
> + case AF_INET: {
> + const struct sockaddr_in *const sockaddr =
> + (struct sockaddr_in *)address;
> + return ntohs(sockaddr->sin_port);
Storing ports in big endian (in rulesets) would avoid converting them
every time the kernel checks a socket port. The above comment should
then be updated too.
> + }
> +#if IS_ENABLED(CONFIG_IPV6)
> + case AF_INET6: {
> + const struct sockaddr_in6 *const sockaddr_ip6 =
> + (struct sockaddr_in6 *)address;
> + return ntohs(sockaddr_ip6->sin6_port);
> + }
> +#endif
> + }
> + WARN_ON_ONCE(1);
> + return 0;
> +}
> +
> +static int check_socket_access(struct socket *sock, struct sockaddr *address, int addrlen, u16 port,
> + access_mask_t access_request)
> +{
> + int ret;
> + bool allowed = false;
> + layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_NET] = {};
> + const struct landlock_rule *rule;
> + access_mask_t handled_access;
> + const struct landlock_id id = {
> + .key.data = port,
> + .type = LANDLOCK_KEY_NET_PORT,
> + };
> + const struct landlock_ruleset *const domain = get_current_net_domain();
> +
> + if (WARN_ON_ONCE(!domain))
> + return 0;
> + if (WARN_ON_ONCE(domain->num_layers < 1))
> + return -EACCES;
> + /* Check if it's a TCP socket. */
> + if (sock->type != SOCK_STREAM)
> + return 0;
> +
> + ret = check_addrlen(address, addrlen);
> + if (ret)
> + return ret;
> +
> + switch (address->sa_family) {
> + case AF_UNSPEC:
> + /*
> + * Connecting to an address with AF_UNSPEC dissolves the TCP
> + * association, which have the same effect as closing the
> + * connection while retaining the socket object (i.e., the file
> + * descriptor). As for dropping privileges, closing
> + * connections is always allowed.
> + */
> + if (access_request == LANDLOCK_ACCESS_NET_CONNECT_TCP)
> + return 0;
> +
> + /*
> + * For compatibility reason, accept AF_UNSPEC for bind
> + * accesses (mapped to AF_INET) only if the address is
> + * INADDR_ANY (cf. __inet_bind). Checking the address is
> + * required to not wrongfully return -EACCES instead of
> + * -EAFNOSUPPORT.
> + */
> + if (access_request == LANDLOCK_ACCESS_NET_BIND_TCP) {
> + const struct sockaddr_in *const sockaddr =
> + (struct sockaddr_in *)address;
> +
> + if (sockaddr->sin_addr.s_addr != htonl(INADDR_ANY))
> + return -EAFNOSUPPORT;
> + }
> +
> + fallthrough;
> + case AF_INET:
> +#if IS_ENABLED(CONFIG_IPV6)
> + case AF_INET6:
> +#endif
> + rule = landlock_find_rule(domain, id);
> + handled_access = landlock_init_layer_masks(
> + domain, access_request, &layer_masks,
> + LANDLOCK_KEY_NET_PORT);
> + allowed = landlock_unmask_layers(rule, handled_access,
> + &layer_masks,
> + ARRAY_SIZE(layer_masks));
> + }
> + return allowed ? 0 : -EACCES;
> +}
> +
> +static int hook_socket_bind(struct socket *sock, struct sockaddr *address,
> + int addrlen)
> +{
> + return check_socket_access(sock, address, addrlen, get_port(address),
> + LANDLOCK_ACCESS_NET_BIND_TCP);
> +}
> +
> +static int hook_socket_connect(struct socket *sock, struct sockaddr *address,
> + int addrlen)
> +{
> + return check_socket_access(sock, address, addrlen, get_port(address),
> + LANDLOCK_ACCESS_NET_CONNECT_TCP);
> +}
[...]
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