@@ -193,7 +193,6 @@ enum bpf_arg_type {
ARG_PTR_TO_CTX, /* pointer to context */
ARG_ANYTHING, /* any (initialized) argument is ok */
- ARG_PTR_TO_SOCKET, /* pointer to bpf_sock */
ARG_PTR_TO_SPIN_LOCK, /* pointer to bpf_spin_lock */
ARG_PTR_TO_SOCK_COMMON, /* pointer to sock_common */
};
@@ -66,6 +66,46 @@ struct bpf_reg_state {
* same reference to the socket, to determine proper reference freeing.
*/
u32 id;
+ /* PTR_TO_SOCKET and PTR_TO_TCP_SOCK could be a ptr returned
+ * from a pointer-cast helper, bpf_sk_fullsock() and
+ * bpf_tcp_sock().
+ *
+ * Consider the following where "sk" is a reference counted
+ * pointer returned from "sk = bpf_sk_lookup_tcp();":
+ *
+ * 1: sk = bpf_sk_lookup_tcp();
+ * 2: if (!sk) { return 0; }
+ * 3: fullsock = bpf_sk_fullsock(sk);
+ * 4: if (!fullsock) { bpf_sk_release(sk); return 0; }
+ * 5: tp = bpf_tcp_sock(fullsock);
+ * 6: if (!tp) { bpf_sk_release(sk); return 0; }
+ * 7: bpf_sk_release(sk);
+ * 8: snd_cwnd = tp->snd_cwnd; // verifier will complain
+ *
+ * After bpf_sk_release(sk) at line 7, both "fullsock" ptr and
+ * "tp" ptr should be invalidated also. In order to do that,
+ * the reg holding "fullsock" and "sk" need to remember
+ * the original refcounted ptr id (i.e. sk_reg->id) in ref_obj_id
+ * such that the verifier can reset all regs which have
+ * ref_obj_id matching the sk_reg->id.
+ *
+ * sk_reg->ref_obj_id is set to sk_reg->id at line 1.
+ * sk_reg->id will stay as NULL-marking purpose only.
+ * After NULL-marking is done, sk_reg->id can be reset to 0.
+ *
+ * After "fullsock = bpf_sk_fullsock(sk);" at line 3,
+ * fullsock_reg->ref_obj_id is set to sk_reg->ref_obj_id.
+ *
+ * After "tp = bpf_tcp_sock(fullsock);" at line 5,
+ * tp_reg->ref_obj_id is set to fullsock_reg->ref_obj_id
+ * which is the same as sk_reg->ref_obj_id.
+ *
+ * From the verifier perspective, if sk, fullsock and tp
+ * are not NULL, they are the same ptr with different
+ * reg->type. In particular, bpf_sk_release(tp) is also
+ * allowed and has the same effect as bpf_sk_release(sk).
+ */
+ u32 ref_obj_id;
/* For scalar types (SCALAR_VALUE), this represents our knowledge of
* the actual value.
* For pointer types, this represents the variable part of the offset
@@ -212,7 +212,7 @@ struct bpf_call_arg_meta {
int access_size;
s64 msize_smax_value;
u64 msize_umax_value;
- int ptr_id;
+ int ref_obj_id;
int func_id;
};
@@ -346,35 +346,15 @@ static bool reg_type_may_be_null(enum bpf_reg_type type)
type == PTR_TO_TCP_SOCK_OR_NULL;
}
-static bool type_is_refcounted(enum bpf_reg_type type)
-{
- return type == PTR_TO_SOCKET;
-}
-
-static bool type_is_refcounted_or_null(enum bpf_reg_type type)
-{
- return type == PTR_TO_SOCKET || type == PTR_TO_SOCKET_OR_NULL;
-}
-
-static bool reg_is_refcounted(const struct bpf_reg_state *reg)
-{
- return type_is_refcounted(reg->type);
-}
-
static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg)
{
return reg->type == PTR_TO_MAP_VALUE &&
map_value_has_spin_lock(reg->map_ptr);
}
-static bool reg_is_refcounted_or_null(const struct bpf_reg_state *reg)
+static bool arg_type_may_be_refcounted(enum bpf_arg_type type)
{
- return type_is_refcounted_or_null(reg->type);
-}
-
-static bool arg_type_is_refcounted(enum bpf_arg_type type)
-{
- return type == ARG_PTR_TO_SOCKET;
+ return type == ARG_PTR_TO_SOCK_COMMON;
}
/* Determine whether the function releases some resources allocated by another
@@ -392,6 +372,12 @@ static bool is_acquire_function(enum bpf_func_id func_id)
func_id == BPF_FUNC_sk_lookup_udp;
}
+static bool is_ptr_cast_function(enum bpf_func_id func_id)
+{
+ return func_id == BPF_FUNC_tcp_sock ||
+ func_id == BPF_FUNC_sk_fullsock;
+}
+
/* string representation of 'enum bpf_reg_type' */
static const char * const reg_type_str[] = {
[NOT_INIT] = "?",
@@ -465,7 +451,8 @@ static void print_verifier_state(struct bpf_verifier_env *env,
if (t == PTR_TO_STACK)
verbose(env, ",call_%d", func(env, reg)->callsite);
} else {
- verbose(env, "(id=%d", reg->id);
+ verbose(env, "(id=%d ref_obj_id=%d", reg->id,
+ reg->ref_obj_id);
if (t != SCALAR_VALUE)
verbose(env, ",off=%d", reg->off);
if (type_is_pkt_pointer(t))
@@ -2414,16 +2401,15 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
/* Any sk pointer can be ARG_PTR_TO_SOCK_COMMON */
if (!type_is_sk_pointer(type))
goto err_type;
- } else if (arg_type == ARG_PTR_TO_SOCKET) {
- expected_type = PTR_TO_SOCKET;
- if (type != expected_type)
- goto err_type;
- if (meta->ptr_id || !reg->id) {
- verbose(env, "verifier internal error: mismatched references meta=%d, reg=%d\n",
- meta->ptr_id, reg->id);
- return -EFAULT;
+ if (reg->ref_obj_id) {
+ if (meta->ref_obj_id) {
+ verbose(env, "verifier internal error: more than one arg with ref_obj_id R%d %u %u\n",
+ regno, reg->ref_obj_id,
+ meta->ref_obj_id);
+ return -EFAULT;
+ }
+ meta->ref_obj_id = reg->ref_obj_id;
}
- meta->ptr_id = reg->id;
} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
if (meta->func_id == BPF_FUNC_spin_lock) {
if (process_spin_lock(env, regno, true))
@@ -2740,32 +2726,38 @@ static bool check_arg_pair_ok(const struct bpf_func_proto *fn)
return true;
}
-static bool check_refcount_ok(const struct bpf_func_proto *fn)
+static bool check_refcount_ok(const struct bpf_func_proto *fn, int func_id)
{
int count = 0;
- if (arg_type_is_refcounted(fn->arg1_type))
+ if (arg_type_may_be_refcounted(fn->arg1_type))
count++;
- if (arg_type_is_refcounted(fn->arg2_type))
+ if (arg_type_may_be_refcounted(fn->arg2_type))
count++;
- if (arg_type_is_refcounted(fn->arg3_type))
+ if (arg_type_may_be_refcounted(fn->arg3_type))
count++;
- if (arg_type_is_refcounted(fn->arg4_type))
+ if (arg_type_may_be_refcounted(fn->arg4_type))
count++;
- if (arg_type_is_refcounted(fn->arg5_type))
+ if (arg_type_may_be_refcounted(fn->arg5_type))
count++;
+ /* A reference acquiring function cannot acquire
+ * another refcounted ptr.
+ */
+ if (is_acquire_function(func_id) && count)
+ return false;
+
/* We only support one arg being unreferenced at the moment,
* which is sufficient for the helper functions we have right now.
*/
return count <= 1;
}
-static int check_func_proto(const struct bpf_func_proto *fn)
+static int check_func_proto(const struct bpf_func_proto *fn, int func_id)
{
return check_raw_mode_ok(fn) &&
check_arg_pair_ok(fn) &&
- check_refcount_ok(fn) ? 0 : -EINVAL;
+ check_refcount_ok(fn, func_id) ? 0 : -EINVAL;
}
/* Packet data might have moved, any old PTR_TO_PACKET[_META,_END]
@@ -2799,19 +2791,20 @@ static void clear_all_pkt_pointers(struct bpf_verifier_env *env)
}
static void release_reg_references(struct bpf_verifier_env *env,
- struct bpf_func_state *state, int id)
+ struct bpf_func_state *state,
+ int ref_obj_id)
{
struct bpf_reg_state *regs = state->regs, *reg;
int i;
for (i = 0; i < MAX_BPF_REG; i++)
- if (regs[i].id == id)
+ if (regs[i].ref_obj_id == ref_obj_id)
mark_reg_unknown(env, regs, i);
bpf_for_each_spilled_reg(i, state, reg) {
if (!reg)
continue;
- if (reg_is_refcounted(reg) && reg->id == id)
+ if (reg->ref_obj_id == ref_obj_id)
__mark_reg_unknown(reg);
}
}
@@ -2820,15 +2813,20 @@ static void release_reg_references(struct bpf_verifier_env *env,
* resources. Identify all copies of the same pointer and clear the reference.
*/
static int release_reference(struct bpf_verifier_env *env,
- struct bpf_call_arg_meta *meta)
+ int ref_obj_id)
{
struct bpf_verifier_state *vstate = env->cur_state;
+ int err;
int i;
+ err = release_reference_state(cur_func(env), ref_obj_id);
+ if (err)
+ return err;
+
for (i = 0; i <= vstate->curframe; i++)
- release_reg_references(env, vstate->frame[i], meta->ptr_id);
+ release_reg_references(env, vstate->frame[i], ref_obj_id);
- return release_reference_state(cur_func(env), meta->ptr_id);
+ return 0;
}
static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
@@ -3047,7 +3045,7 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
memset(&meta, 0, sizeof(meta));
meta.pkt_access = fn->pkt_access;
- err = check_func_proto(fn);
+ err = check_func_proto(fn, func_id);
if (err) {
verbose(env, "kernel subsystem misconfigured func %s#%d\n",
func_id_name(func_id), func_id);
@@ -3093,7 +3091,7 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
return err;
}
} else if (is_release_function(func_id)) {
- err = release_reference(env, &meta);
+ err = release_reference(env, meta.ref_obj_id);
if (err) {
verbose(env, "func %s#%d reference has not been acquired before\n",
func_id_name(func_id), func_id);
@@ -3154,8 +3152,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
if (id < 0)
return id;
- /* For release_reference() */
+ /* For mark_ptr_or_null_reg() */
regs[BPF_REG_0].id = id;
+ /* For release_reference() */
+ regs[BPF_REG_0].ref_obj_id = id;
} else {
/* For mark_ptr_or_null_reg() */
regs[BPF_REG_0].id = ++env->id_gen;
@@ -3170,6 +3170,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
return -EINVAL;
}
+ if (is_ptr_cast_function(func_id))
+ /* For release_reference() */
+ regs[BPF_REG_0].ref_obj_id = meta.ref_obj_id;
+
do_refine_retval_range(regs, fn->ret_type, func_id, &meta);
err = check_map_func_compatibility(env, meta.map_ptr, func_id);
@@ -4665,11 +4669,19 @@ static void mark_ptr_or_null_reg(struct bpf_func_state *state,
} else if (reg->type == PTR_TO_TCP_SOCK_OR_NULL) {
reg->type = PTR_TO_TCP_SOCK;
}
- if (is_null || !(reg_is_refcounted(reg) ||
- reg_may_point_to_spin_lock(reg))) {
- /* We don't need id from this point onwards anymore,
- * thus we should better reset it, so that state
- * pruning has chances to take effect.
+ if (is_null) {
+ /* We don't need id and ref_obj_id from this point
+ * onwards anymore, thus we should better reset it,
+ * so that state pruning has chances to take effect.
+ */
+ reg->id = 0;
+ reg->ref_obj_id = 0;
+ } else if (!reg_may_point_to_spin_lock(reg)) {
+ /* For not-NULL ptr, reg->ref_obj_id will be reset
+ * in release_reg_references().
+ *
+ * reg->id is still used by spin_lock ptr. Other
+ * than spin_lock ptr type, reg->id can be reset.
*/
reg->id = 0;
}
@@ -4684,11 +4696,16 @@ static void mark_ptr_or_null_regs(struct bpf_verifier_state *vstate, u32 regno,
{
struct bpf_func_state *state = vstate->frame[vstate->curframe];
struct bpf_reg_state *reg, *regs = state->regs;
+ u32 ref_obj_id = regs[regno].ref_obj_id;
u32 id = regs[regno].id;
int i, j;
- if (reg_is_refcounted_or_null(®s[regno]) && is_null)
- release_reference_state(state, id);
+ if (ref_obj_id && ref_obj_id == id && is_null)
+ /* regs[regno] is in the " == NULL" branch.
+ * No one could have freed the reference state before
+ * doing the NULL check.
+ */
+ WARN_ON_ONCE(release_reference_state(state, id));
for (i = 0; i < MAX_BPF_REG; i++)
mark_ptr_or_null_reg(state, ®s[i], id, is_null);
@@ -1796,8 +1796,6 @@ static const struct bpf_func_proto bpf_skb_pull_data_proto = {
BPF_CALL_1(bpf_sk_fullsock, struct sock *, sk)
{
- sk = sk_to_full_sk(sk);
-
return sk_fullsock(sk) ? (unsigned long)sk : (unsigned long)NULL;
}
@@ -5266,7 +5264,7 @@ static const struct bpf_func_proto bpf_sk_release_proto = {
.func = bpf_sk_release,
.gpl_only = false,
.ret_type = RET_INTEGER,
- .arg1_type = ARG_PTR_TO_SOCKET,
+ .arg1_type = ARG_PTR_TO_SOCK_COMMON,
};
BPF_CALL_5(bpf_xdp_sk_lookup_udp, struct xdp_buff *, ctx,
@@ -5407,8 +5405,6 @@ u32 bpf_tcp_sock_convert_ctx_access(enum bpf_access_type type,
BPF_CALL_1(bpf_tcp_sock, struct sock *, sk)
{
- sk = sk_to_full_sk(sk);
-
if (sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP)
return (unsigned long)sk;
Lorenz Bauer [thanks!] reported that a ptr returned by bpf_tcp_sock(sk) can still be accessed after bpf_sk_release(sk). Both bpf_tcp_sock() and bpf_sk_fullsock() have the same issue. This patch addresses them together. A simple reproducer looks like this: sk = bpf_sk_lookup_tcp(); /* if (!sk) ... */ tp = bpf_tcp_sock(sk); /* if (!tp) ... */ bpf_sk_release(sk); snd_cwnd = tp->snd_cwnd; /* oops! The verifier does not complain. */ The problem is the verifier did not scrub the register's states of the tcp_sock ptr (tp) after bpf_sk_release(sk). [ Note that when calling bpf_tcp_sock(sk), the sk is not always refcount-acquired. e.g. bpf_tcp_sock(skb->sk). The verifier works fine for this case. ] Currently, the verifier does not track if a helper's return ptr (in REG_0) is "carry"-ing one of its argument's refcount status. To carry this info, the reg1->id needs to be stored in reg0. One approach was tried, like "reg0->id = reg1->id", when calling "bpf_tcp_sock()". The main idea was to avoid adding another "ref_obj_id" for the same reg. However, overlapping the NULL marking and ref tracking purpose in one "id" does not work well: ref_sk = bpf_sk_lookup_tcp(); fullsock = bpf_sk_fullsock(ref_sk); tp = bpf_tcp_sock(ref_sk); if (!fullsock) { bpf_sk_release(ref_sk); return 0; } /* fullsock_reg->id is marked for NOT-NULL. * Same for tp_reg->id because they have the same id. */ /* oops. verifier did not complain about the missing !tp check */ snd_cwnd = tp->snd_cwnd; Hence, a new "ref_obj_id" is needed in "struct bpf_reg_state". With a new ref_obj_id, when bpf_sk_release(sk) is called, the verifier can scrub all reg states which has a ref_obj_id match. It is done with the changes in release_reg_references() in this patch. While fixing it, sk_to_full_sk() is removed from bpf_tcp_sock() and bpf_sk_fullsock() to avoid these helpers from returning another ptr. It will make bpf_sk_release(tp) possible: sk = bpf_sk_lookup_tcp(); /* if (!sk) ... */ tp = bpf_tcp_sock(sk); /* if (!tp) ... */ bpf_sk_release(tp); A separate helper "bpf_get_listener_sock()" will be added in a later patch to do sk_to_full_sk(). Misc change notes: - To allow bpf_sk_release(tp), the arg of bpf_sk_release() is changed from ARG_PTR_TO_SOCKET to ARG_PTR_TO_SOCK_COMMON. ARG_PTR_TO_SOCKET is removed from bpf.h since no helper is using it. - arg_type_is_refcounted() is renamed to arg_type_may_be_refcounted() because ARG_PTR_TO_SOCK_COMMON is the only one and skb->sk is not refcounted. All bpf_sk_release(), bpf_sk_fullsock() and bpf_tcp_sock() take ARG_PTR_TO_SOCK_COMMON. - check_refcount_ok() ensures is_acquire_function() cannot take arg_type_may_be_refcounted() as its argument. - The check_func_arg() can only allow one refcount-ed arg. It is guaranteed by check_refcount_ok() which ensures at most one arg can be refcounted. Hence, it is a verifier internal error if >1 refcount arg found in check_func_arg(). - In release_reference(), release_reference_state() is called first to ensure a match on "reg->ref_obj_id" can be found before scrubbing the reg states with release_reg_references(). - reg_is_refcounted() is no longer needed. 1. In mark_ptr_or_null_regs(), its usage is replaced by "ref_obj_id && ref_obj_id == id" because, when is_null == true, release_reference_state() should only be called on the ref_obj_id obtained by a acquire helper (i.e. is_acquire_function() == true). Otherwise, the following would happen: sk = bpf_sk_lookup_tcp(); /* if (!sk) { ... } */ fullsock = bpf_sk_fullsock(sk); if (!fullsock) { /* * release_reference_state(fullsock_reg->ref_obj_id) * where fullsock_reg->ref_obj_id == sk_reg->ref_obj_id. * * Hence, the following bpf_sk_release(sk) will fail * because the ref state has already been released in the * earlier release_reference_state(fullsock_reg->ref_obj_id). */ bpf_sk_release(sk); } 2. In release_reg_references(), the current reg_is_refcounted() call is unnecessary because the id check is enough. - The type_is_refcounted() and type_is_refcounted_or_null() are no longer needed also because reg_is_refcounted() is removed. Fixes: 655a51e536c0 ("bpf: Add struct bpf_tcp_sock and BPF_FUNC_tcp_sock") Reported-by: Lorenz Bauer <lmb@cloudflare.com> Signed-off-by: Martin KaFai Lau <kafai@fb.com> --- include/linux/bpf.h | 1 - include/linux/bpf_verifier.h | 40 +++++++++++ kernel/bpf/verifier.c | 131 ++++++++++++++++++++--------------- net/core/filter.c | 6 +- 4 files changed, 115 insertions(+), 63 deletions(-)