bpf, sockmap: fix sock_map_ctx_update_elem race with exist/noexist
The current code in sock_map_ctx_update_elem() allows for BPF_EXIST
and BPF_NOEXIST map update flags. While on array-like maps this approach
is rather uncommon, e.g. bpf_fd_array_map_update_elem() and others
enforce map update flags to be BPF_ANY such that xchg() can be used
directly, the current implementation in sock map does not guarantee
that such operation with BPF_EXIST / BPF_NOEXIST is atomic.
The initial test does a READ_ONCE(stab->sock_map[i]) to fetch the
socket from the slot which is then tested for NULL / non-NULL. However
later after __sock_map_ctx_update_elem(), the actual update is done
through osock = xchg(&stab->sock_map[i], sock). Problem is that in
the meantime a different CPU could have updated / deleted a socket
on that specific slot and thus flag contraints won't hold anymore.
I've been thinking whether best would be to just break UAPI and do
an enforcement of BPF_ANY to check if someone actually complains,
however trouble is that already in BPF kselftest we use BPF_NOEXIST
for the map update, and therefore it might have been copied into
applications already. The fix to keep the current behavior intact
would be to add a map lock similar to the sock hash bucket lock only
for covering the whole map.
Fixes: 174a79ff95 ("bpf: sockmap with sk redirect support")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann
Alexei Starovoitov
Родитель
166ab6f0a0
Коммит
585f5a6252
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@ -58,6 +58,7 @@ struct bpf_stab {
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struct bpf_map map;
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struct sock **sock_map;
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struct bpf_sock_progs progs;
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raw_spinlock_t lock;
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};
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struct bucket {
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@ -89,9 +90,9 @@ enum smap_psock_state {
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struct smap_psock_map_entry {
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struct list_head list;
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struct bpf_map *map;
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struct sock **entry;
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struct htab_elem __rcu *hash_link;
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struct bpf_htab __rcu *htab;
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};
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struct smap_psock {
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@ -343,13 +344,18 @@ static void bpf_tcp_close(struct sock *sk, long timeout)
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e = psock_map_pop(sk, psock);
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while (e) {
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if (e->entry) {
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osk = cmpxchg(e->entry, sk, NULL);
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struct bpf_stab *stab = container_of(e->map, struct bpf_stab, map);
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raw_spin_lock_bh(&stab->lock);
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osk = *e->entry;
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if (osk == sk) {
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*e->entry = NULL;
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smap_release_sock(psock, sk);
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}
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raw_spin_unlock_bh(&stab->lock);
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} else {
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struct htab_elem *link = rcu_dereference(e->hash_link);
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struct bpf_htab *htab = rcu_dereference(e->htab);
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struct bpf_htab *htab = container_of(e->map, struct bpf_htab, map);
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struct hlist_head *head;
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struct htab_elem *l;
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struct bucket *b;
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@ -1642,6 +1648,7 @@ static struct bpf_map *sock_map_alloc(union bpf_attr *attr)
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return ERR_PTR(-ENOMEM);
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bpf_map_init_from_attr(&stab->map, attr);
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raw_spin_lock_init(&stab->lock);
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/* make sure page count doesn't overflow */
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cost = (u64) stab->map.max_entries * sizeof(struct sock *);
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@ -1716,14 +1723,15 @@ static void sock_map_free(struct bpf_map *map)
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* and a grace period expire to ensure psock is really safe to remove.
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*/
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rcu_read_lock();
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raw_spin_lock_bh(&stab->lock);
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for (i = 0; i < stab->map.max_entries; i++) {
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struct smap_psock *psock;
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struct sock *sock;
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sock = xchg(&stab->sock_map[i], NULL);
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sock = stab->sock_map[i];
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if (!sock)
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continue;
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stab->sock_map[i] = NULL;
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psock = smap_psock_sk(sock);
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/* This check handles a racing sock event that can get the
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* sk_callback_lock before this case but after xchg happens
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@ -1735,6 +1743,7 @@ static void sock_map_free(struct bpf_map *map)
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smap_release_sock(psock, sock);
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}
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}
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raw_spin_unlock_bh(&stab->lock);
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rcu_read_unlock();
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sock_map_remove_complete(stab);
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@ -1778,14 +1787,16 @@ static int sock_map_delete_elem(struct bpf_map *map, void *key)
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if (k >= map->max_entries)
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return -EINVAL;
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sock = xchg(&stab->sock_map[k], NULL);
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raw_spin_lock_bh(&stab->lock);
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sock = stab->sock_map[k];
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stab->sock_map[k] = NULL;
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raw_spin_unlock_bh(&stab->lock);
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if (!sock)
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return -EINVAL;
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psock = smap_psock_sk(sock);
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if (!psock)
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goto out;
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return 0;
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if (psock->bpf_parse) {
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write_lock_bh(&sock->sk_callback_lock);
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smap_stop_sock(psock, sock);
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@ -1793,7 +1804,6 @@ static int sock_map_delete_elem(struct bpf_map *map, void *key)
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}
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smap_list_map_remove(psock, &stab->sock_map[k]);
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smap_release_sock(psock, sock);
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out:
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return 0;
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}
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@ -1829,11 +1839,9 @@ out:
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static int __sock_map_ctx_update_elem(struct bpf_map *map,
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struct bpf_sock_progs *progs,
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struct sock *sock,
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struct sock **map_link,
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void *key)
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{
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struct bpf_prog *verdict, *parse, *tx_msg;
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struct smap_psock_map_entry *e = NULL;
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struct smap_psock *psock;
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bool new = false;
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int err = 0;
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@ -1906,14 +1914,6 @@ static int __sock_map_ctx_update_elem(struct bpf_map *map,
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new = true;
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}
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if (map_link) {
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e = kzalloc(sizeof(*e), GFP_ATOMIC | __GFP_NOWARN);
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if (!e) {
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err = -ENOMEM;
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goto out_free;
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}
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}
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/* 3. At this point we have a reference to a valid psock that is
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* running. Attach any BPF programs needed.
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*/
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@ -1935,17 +1935,6 @@ static int __sock_map_ctx_update_elem(struct bpf_map *map,
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write_unlock_bh(&sock->sk_callback_lock);
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}
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/* 4. Place psock in sockmap for use and stop any programs on
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* the old sock assuming its not the same sock we are replacing
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* it with. Because we can only have a single set of programs if
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* old_sock has a strp we can stop it.
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*/
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if (map_link) {
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e->entry = map_link;
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spin_lock_bh(&psock->maps_lock);
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list_add_tail(&e->list, &psock->maps);
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spin_unlock_bh(&psock->maps_lock);
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}
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return err;
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out_free:
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smap_release_sock(psock, sock);
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@ -1956,7 +1945,6 @@ out_progs:
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}
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if (tx_msg)
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bpf_prog_put(tx_msg);
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kfree(e);
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return err;
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}
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@ -1966,36 +1954,57 @@ static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops,
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{
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struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
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struct bpf_sock_progs *progs = &stab->progs;
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struct sock *osock, *sock;
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struct sock *osock, *sock = skops->sk;
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struct smap_psock_map_entry *e;
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struct smap_psock *psock;
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u32 i = *(u32 *)key;
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int err;
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if (unlikely(flags > BPF_EXIST))
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return -EINVAL;
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if (unlikely(i >= stab->map.max_entries))
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return -E2BIG;
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sock = READ_ONCE(stab->sock_map[i]);
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if (flags == BPF_EXIST && !sock)
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return -ENOENT;
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else if (flags == BPF_NOEXIST && sock)
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return -EEXIST;
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e = kzalloc(sizeof(*e), GFP_ATOMIC | __GFP_NOWARN);
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if (!e)
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return -ENOMEM;
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sock = skops->sk;
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err = __sock_map_ctx_update_elem(map, progs, sock, &stab->sock_map[i],
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key);
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err = __sock_map_ctx_update_elem(map, progs, sock, key);
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if (err)
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goto out;
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osock = xchg(&stab->sock_map[i], sock);
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if (osock) {
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struct smap_psock *opsock = smap_psock_sk(osock);
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smap_list_map_remove(opsock, &stab->sock_map[i]);
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smap_release_sock(opsock, osock);
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/* psock guaranteed to be present. */
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psock = smap_psock_sk(sock);
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raw_spin_lock_bh(&stab->lock);
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osock = stab->sock_map[i];
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if (osock && flags == BPF_NOEXIST) {
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err = -EEXIST;
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goto out_unlock;
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}
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if (!osock && flags == BPF_EXIST) {
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err = -ENOENT;
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goto out_unlock;
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}
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e->entry = &stab->sock_map[i];
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e->map = map;
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spin_lock_bh(&psock->maps_lock);
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list_add_tail(&e->list, &psock->maps);
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spin_unlock_bh(&psock->maps_lock);
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stab->sock_map[i] = sock;
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if (osock) {
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psock = smap_psock_sk(osock);
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smap_list_map_remove(psock, &stab->sock_map[i]);
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smap_release_sock(psock, osock);
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}
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raw_spin_unlock_bh(&stab->lock);
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return 0;
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out_unlock:
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smap_release_sock(psock, sock);
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raw_spin_unlock_bh(&stab->lock);
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out:
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kfree(e);
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return err;
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}
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@ -2358,7 +2367,7 @@ static int sock_hash_ctx_update_elem(struct bpf_sock_ops_kern *skops,
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b = __select_bucket(htab, hash);
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head = &b->head;
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err = __sock_map_ctx_update_elem(map, progs, sock, NULL, key);
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err = __sock_map_ctx_update_elem(map, progs, sock, key);
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if (err)
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goto err;
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@ -2384,8 +2393,7 @@ static int sock_hash_ctx_update_elem(struct bpf_sock_ops_kern *skops,
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}
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rcu_assign_pointer(e->hash_link, l_new);
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rcu_assign_pointer(e->htab,
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container_of(map, struct bpf_htab, map));
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e->map = map;
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spin_lock_bh(&psock->maps_lock);
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list_add_tail(&e->list, &psock->maps);
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spin_unlock_bh(&psock->maps_lock);
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