[PATCH bpf-next] bpf: Fix verifier assumptions about socket->sk

[PATCH bpf-next] bpf: Fix verifier assumptions about socket->sk

[Alexei Starovoitov]

From: Alexei Starovoitov <ast@kernel.org>

The verifier assumes that 'sk' field in 'struct socket' is valid
and non-NULL when 'socket' pointer itself is trusted and non-NULL.
That may not be the case when socket was just created and
passed to LSM socket_accept hook.
Fix this verifier assumption and adjust tests.

Reported-by: Liam Wisehart <liamwisehart@meta.com>
Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/verifier.c                         | 23 +++++++++++++++----
 .../selftests/bpf/progs/local_storage.c       | 20 ++++++++--------
 .../testing/selftests/bpf/progs/lsm_cgroup.c  |  8 +++++--
 3 files changed, 35 insertions(+), 16 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4e474ef44e9c..c2780a5c396a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2368,6 +2368,8 @@ static void mark_btf_ld_reg(struct bpf_verifier_env *env,
 	regs[regno].type = PTR_TO_BTF_ID | flag;
 	regs[regno].btf = btf;
 	regs[regno].btf_id = btf_id;
+	if (type_may_be_null(flag))
+		regs[regno].id = ++env->id_gen;
 }
 
 #define DEF_NOT_SUBREG	(0)
@@ -5400,8 +5402,6 @@ static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
 		 */
 		mark_btf_ld_reg(env, cur_regs(env), value_regno, PTR_TO_BTF_ID, kptr_field->kptr.btf,
 				kptr_field->kptr.btf_id, btf_ld_kptr_type(env, kptr_field));
-		/* For mark_ptr_or_null_reg */
-		val_reg->id = ++env->id_gen;
 	} else if (class == BPF_STX) {
 		val_reg = reg_state(env, value_regno);
 		if (!register_is_null(val_reg) &&
@@ -5719,7 +5719,8 @@ static bool is_trusted_reg(const struct bpf_reg_state *reg)
 		return true;
 
 	/* Types listed in the reg2btf_ids are always trusted */
-	if (reg2btf_ids[base_type(reg->type)])
+	if (reg2btf_ids[base_type(reg->type)] &&
+	    !bpf_type_has_unsafe_modifiers(reg->type))
 		return true;
 
 	/* If a register is not referenced, it is trusted if it has the
@@ -6339,6 +6340,7 @@ static int bpf_map_direct_read(struct bpf_map *map, int off, int size, u64 *val,
 #define BTF_TYPE_SAFE_RCU(__type)  __PASTE(__type, __safe_rcu)
 #define BTF_TYPE_SAFE_RCU_OR_NULL(__type)  __PASTE(__type, __safe_rcu_or_null)
 #define BTF_TYPE_SAFE_TRUSTED(__type)  __PASTE(__type, __safe_trusted)
+#define BTF_TYPE_SAFE_TRUSTED_OR_NULL(__type)  __PASTE(__type, __safe_trusted_or_null)
 
 /*
  * Allow list few fields as RCU trusted or full trusted.
@@ -6402,7 +6404,7 @@ BTF_TYPE_SAFE_TRUSTED(struct dentry) {
 	struct inode *d_inode;
 };
 
-BTF_TYPE_SAFE_TRUSTED(struct socket) {
+BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket) {
 	struct sock *sk;
 };
 
@@ -6437,11 +6439,20 @@ static bool type_is_trusted(struct bpf_verifier_env *env,
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct linux_binprm));
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct file));
 	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct dentry));
-	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED(struct socket));
 
 	return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id, "__safe_trusted");
 }
 
+static bool type_is_trusted_or_null(struct bpf_verifier_env *env,
+				    struct bpf_reg_state *reg,
+				    const char *field_name, u32 btf_id)
+{
+	BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket));
+
+	return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id,
+					  "__safe_trusted_or_null");
+}
+
 static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
 				   struct bpf_reg_state *regs,
 				   int regno, int off, int size,
@@ -6550,6 +6561,8 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
 		 */
 		if (type_is_trusted(env, reg, field_name, btf_id)) {
 			flag |= PTR_TRUSTED;
+		} else if (type_is_trusted_or_null(env, reg, field_name, btf_id)) {
+			flag |= PTR_TRUSTED | PTR_MAYBE_NULL;
 		} else if (in_rcu_cs(env) && !type_may_be_null(reg->type)) {
 			if (type_is_rcu(env, reg, field_name, btf_id)) {
 				/* ignore __rcu tag and mark it MEM_RCU */
diff --git a/tools/testing/selftests/bpf/progs/local_storage.c b/tools/testing/selftests/bpf/progs/local_storage.c
index e5e3a8b8dd07..637e75df2e14 100644
--- a/tools/testing/selftests/bpf/progs/local_storage.c
+++ b/tools/testing/selftests/bpf/progs/local_storage.c
@@ -140,11 +140,12 @@ int BPF_PROG(socket_bind, struct socket *sock, struct sockaddr *address,
 {
 	__u32 pid = bpf_get_current_pid_tgid() >> 32;
 	struct local_storage *storage;
+	struct sock *sk = sock->sk;
 
-	if (pid != monitored_pid)
+	if (pid != monitored_pid || !sk)
 		return 0;
 
-	storage = bpf_sk_storage_get(&sk_storage_map, sock->sk, 0, 0);
+	storage = bpf_sk_storage_get(&sk_storage_map, sk, 0, 0);
 	if (!storage)
 		return 0;
 
@@ -155,24 +156,24 @@ int BPF_PROG(socket_bind, struct socket *sock, struct sockaddr *address,
 	/* This tests that we can associate multiple elements
 	 * with the local storage.
 	 */
-	storage = bpf_sk_storage_get(&sk_storage_map2, sock->sk, 0,
+	storage = bpf_sk_storage_get(&sk_storage_map2, sk, 0,
 				     BPF_LOCAL_STORAGE_GET_F_CREATE);
 	if (!storage)
 		return 0;
 
-	if (bpf_sk_storage_delete(&sk_storage_map2, sock->sk))
+	if (bpf_sk_storage_delete(&sk_storage_map2, sk))
 		return 0;
 
-	storage = bpf_sk_storage_get(&sk_storage_map2, sock->sk, 0,
+	storage = bpf_sk_storage_get(&sk_storage_map2, sk, 0,
 				     BPF_LOCAL_STORAGE_GET_F_CREATE);
 	if (!storage)
 		return 0;
 
-	if (bpf_sk_storage_delete(&sk_storage_map, sock->sk))
+	if (bpf_sk_storage_delete(&sk_storage_map, sk))
 		return 0;
 
 	/* Ensure that the sk_storage_map is disconnected from the storage. */
-	if (!sock->sk->sk_bpf_storage || sock->sk->sk_bpf_storage->smap)
+	if (!sk->sk_bpf_storage || sk->sk_bpf_storage->smap)
 		return 0;
 
 	sk_storage_result = 0;
@@ -185,11 +186,12 @@ int BPF_PROG(socket_post_create, struct socket *sock, int family, int type,
 {
 	__u32 pid = bpf_get_current_pid_tgid() >> 32;
 	struct local_storage *storage;
+	struct sock *sk = sock->sk;
 
-	if (pid != monitored_pid)
+	if (pid != monitored_pid || !sk)
 		return 0;
 
-	storage = bpf_sk_storage_get(&sk_storage_map, sock->sk, 0,
+	storage = bpf_sk_storage_get(&sk_storage_map, sk, 0,
 				     BPF_LOCAL_STORAGE_GET_F_CREATE);
 	if (!storage)
 		return 0;
diff --git a/tools/testing/selftests/bpf/progs/lsm_cgroup.c b/tools/testing/selftests/bpf/progs/lsm_cgroup.c
index 02c11d16b692..d7598538aa2d 100644
--- a/tools/testing/selftests/bpf/progs/lsm_cgroup.c
+++ b/tools/testing/selftests/bpf/progs/lsm_cgroup.c
@@ -103,11 +103,15 @@ static __always_inline int real_bind(struct socket *sock,
 				     int addrlen)
 {
 	struct sockaddr_ll sa = {};
+	struct sock *sk = sock->sk;
 
-	if (sock->sk->__sk_common.skc_family != AF_PACKET)
+	if (!sk)
+		return 1;
+
+	if (sk->__sk_common.skc_family != AF_PACKET)
 		return 1;
 
-	if (sock->sk->sk_kern_sock)
+	if (sk->sk_kern_sock)
 		return 1;
 
 	bpf_probe_read_kernel(&sa, sizeof(sa), address);
-- 
2.43.0

Re: [PATCH bpf-next] bpf: Fix verifier assumptions about socket->sk

[Andrii Nakryiko]

On Fri, Apr 26, 2024 at 11:56 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> The verifier assumes that 'sk' field in 'struct socket' is valid
> and non-NULL when 'socket' pointer itself is trusted and non-NULL.
> That may not be the case when socket was just created and
> passed to LSM socket_accept hook.
> Fix this verifier assumption and adjust tests.
>
> Reported-by: Liam Wisehart <liamwisehart@meta.com>
> Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.")
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
>  kernel/bpf/verifier.c                         | 23 +++++++++++++++----
>  .../selftests/bpf/progs/local_storage.c       | 20 ++++++++--------
>  .../testing/selftests/bpf/progs/lsm_cgroup.c  |  8 +++++--
>  3 files changed, 35 insertions(+), 16 deletions(-)
>

Makes sense, but can you also fix up one of benchmark's programs, see
[0], veristat-based CI run caught success->failure change (in
bench_local_storage_create.bpf.o)

  [0] https://github.com/kernel-patches/bpf/actions/runs/8853140420/job/24313511057

pw-bot: cr

> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 4e474ef44e9c..c2780a5c396a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2368,6 +2368,8 @@ static void mark_btf_ld_reg(struct bpf_verifier_env *env,
>         regs[regno].type = PTR_TO_BTF_ID | flag;
>         regs[regno].btf = btf;
>         regs[regno].btf_id = btf_id;
> +       if (type_may_be_null(flag))
> +               regs[regno].id = ++env->id_gen;
>  }
>
>  #define DEF_NOT_SUBREG (0)

[...]

Re: [PATCH bpf-next] bpf: Fix verifier assumptions about socket->sk

[Kumar Kartikeya Dwivedi]

On Fri, 26 Apr 2024 at 20:56, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> From: Alexei Starovoitov <ast@kernel.org>
>
> The verifier assumes that 'sk' field in 'struct socket' is valid
> and non-NULL when 'socket' pointer itself is trusted and non-NULL.
> That may not be the case when socket was just created and
> passed to LSM socket_accept hook.
> Fix this verifier assumption and adjust tests.
>
> Reported-by: Liam Wisehart <liamwisehart@meta.com>
> Fixes: 6fcd486b3a0a ("bpf: Refactor RCU enforcement in the verifier.")
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>