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bpf: tcp: Make sure iter->batch always contains a full bucket snapshot

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Require that iter->batch always contains a full bucket snapshot. This
invariant is important to avoid skipping or repeating sockets during
iteration when combined with the next few patches. Before, there were
two cases where a call to bpf_iter_tcp_batch may only capture part of a
bucket:

1. When bpf_iter_tcp_realloc_batch() returns -ENOMEM.
2. When more sockets are added to the bucket while calling
   bpf_iter_tcp_realloc_batch(), making the updated batch size
   insufficient.

In cases where the batch size only covers part of a bucket, it is
possible to forget which sockets were already visited, especially if we
have to process a bucket in more than two batches. This forces us to
choose between repeating or skipping sockets, so don't allow this:

1. Stop iteration and propagate -ENOMEM up to userspace if reallocation
   fails instead of continuing with a partial batch.
2. Try bpf_iter_tcp_realloc_batch() with GFP_USER just as before, but if
   we still aren't able to capture the full bucket, call
   bpf_iter_tcp_realloc_batch() again while holding the bucket lock to
   guarantee the bucket does not change. On the second attempt use
   GFP_NOWAIT since we hold onto the spin lock.

I did some manual testing to exercise the code paths where GFP_NOWAIT is
used and where ERR_PTR(err) is returned. I used the realloc test cases
included later in this series to trigger a scenario where a realloc
happens inside bpf_iter_tcp_batch and made a small code tweak to force
the first realloc attempt to allocate a too-small batch, thus requiring
another attempt with GFP_NOWAIT. Some printks showed both reallocs with
the tests passing:

Jun 27 00:00:53 crow kernel: again GFP_USER
Jun 27 00:00:53 crow kernel: again GFP_NOWAIT
Jun 27 00:00:53 crow kernel: again GFP_USER
Jun 27 00:00:53 crow kernel: again GFP_NOWAIT

With this setup, I also forced each of the bpf_iter_tcp_realloc_batch
calls to return -ENOMEM to ensure that iteration ends and that the
read() in userspace fails.

Signed-off-by: Jordan Rife <jordan@jrife.io>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
This commit is contained in:
Jordan Rife
2025-07-14 11:09:06 -07:00
committed by Martin KaFai Lau
parent 8271bec9fc
commit cdec67a489
1 changed files with 78 additions and 33 deletions
Download Patch File Download Diff File Expand all files Collapse all files

111
net/ipv4/tcp_ipv4.c
View File

@@ -3057,7 +3057,7 @@ static int bpf_iter_tcp_realloc_batch(struct bpf_tcp_iter_state *iter,
if (!new_batch)
return -ENOMEM;
bpf_iter_tcp_put_batch(iter);
memcpy(new_batch, iter->batch, sizeof(*iter->batch) * iter->end_sk);
kvfree(iter->batch);
iter->batch = new_batch;
iter->max_sk = new_batch_sz;
@@ -3066,69 +3066,95 @@ static int bpf_iter_tcp_realloc_batch(struct bpf_tcp_iter_state *iter,
}
static unsigned int bpf_iter_tcp_listening_batch(struct seq_file *seq,
struct sock *start_sk)
struct sock **start_sk)
{
struct inet_hashinfo *hinfo = seq_file_net(seq)->ipv4.tcp_death_row.hashinfo;
struct bpf_tcp_iter_state *iter = seq->private;
struct tcp_iter_state *st = &iter->state;
struct hlist_nulls_node *node;
unsigned int expected = 1;
struct sock *sk;
sock_hold(start_sk);
iter->batch[iter->end_sk++] = start_sk;
sock_hold(*start_sk);
iter->batch[iter->end_sk++] = *start_sk;
sk = sk_nulls_next(start_sk);
sk = sk_nulls_next(*start_sk);
*start_sk = NULL;
sk_nulls_for_each_from(sk, node) {
if (seq_sk_match(seq, sk)) {
if (iter->end_sk < iter->max_sk) {
sock_hold(sk);
iter->batch[iter->end_sk++] = sk;
} else if (!*start_sk) {
/* Remember where we left off. */
*start_sk = sk;
}
expected++;
}
}
spin_unlock(&hinfo->lhash2[st->bucket].lock);
return expected;
}
static unsigned int bpf_iter_tcp_established_batch(struct seq_file *seq,
struct sock *start_sk)
struct sock **start_sk)
{
struct inet_hashinfo *hinfo = seq_file_net(seq)->ipv4.tcp_death_row.hashinfo;
struct bpf_tcp_iter_state *iter = seq->private;
struct tcp_iter_state *st = &iter->state;
struct hlist_nulls_node *node;
unsigned int expected = 1;
struct sock *sk;
sock_hold(start_sk);
iter->batch[iter->end_sk++] = start_sk;
sock_hold(*start_sk);
iter->batch[iter->end_sk++] = *start_sk;
sk = sk_nulls_next(start_sk);
sk = sk_nulls_next(*start_sk);
*start_sk = NULL;
sk_nulls_for_each_from(sk, node) {
if (seq_sk_match(seq, sk)) {
if (iter->end_sk < iter->max_sk) {
sock_hold(sk);
iter->batch[iter->end_sk++] = sk;
} else if (!*start_sk) {
/* Remember where we left off. */
*start_sk = sk;
}
expected++;
}
}
spin_unlock_bh(inet_ehash_lockp(hinfo, st->bucket));
return expected;
}
static unsigned int bpf_iter_fill_batch(struct seq_file *seq,
struct sock **start_sk)
{
struct bpf_tcp_iter_state *iter = seq->private;
struct tcp_iter_state *st = &iter->state;
if (st->state == TCP_SEQ_STATE_LISTENING)
return bpf_iter_tcp_listening_batch(seq, start_sk);
else
return bpf_iter_tcp_established_batch(seq, start_sk);
}
static void bpf_iter_tcp_unlock_bucket(struct seq_file *seq)
{
struct inet_hashinfo *hinfo = seq_file_net(seq)->ipv4.tcp_death_row.hashinfo;
struct bpf_tcp_iter_state *iter = seq->private;
struct tcp_iter_state *st = &iter->state;
if (st->state == TCP_SEQ_STATE_LISTENING)
spin_unlock(&hinfo->lhash2[st->bucket].lock);
else
spin_unlock_bh(inet_ehash_lockp(hinfo, st->bucket));
}
static struct sock *bpf_iter_tcp_batch(struct seq_file *seq)
{
struct inet_hashinfo *hinfo = seq_file_net(seq)->ipv4.tcp_death_row.hashinfo;
struct bpf_tcp_iter_state *iter = seq->private;
struct tcp_iter_state *st = &iter->state;
unsigned int expected;
bool resized = false;
struct sock *sk;
int err;
/* The st->bucket is done. Directly advance to the next
* bucket instead of having the tcp_seek_last_pos() to skip
@@ -3145,33 +3171,52 @@ static struct sock *bpf_iter_tcp_batch(struct seq_file *seq)
}
}
again:
/* Get a new batch */
iter->cur_sk = 0;
iter->end_sk = 0;
iter->st_bucket_done = false;
iter->st_bucket_done = true;
sk = tcp_seek_last_pos(seq);
if (!sk)
return NULL; /* Done */
if (st->state == TCP_SEQ_STATE_LISTENING)
expected = bpf_iter_tcp_listening_batch(seq, sk);
else
expected = bpf_iter_tcp_established_batch(seq, sk);
expected = bpf_iter_fill_batch(seq, &sk);
if (likely(iter->end_sk == expected))
goto done;
if (iter->end_sk == expected) {
iter->st_bucket_done = true;
return sk;
/* Batch size was too small. */
bpf_iter_tcp_unlock_bucket(seq);
bpf_iter_tcp_put_batch(iter);
err = bpf_iter_tcp_realloc_batch(iter, expected * 3 / 2,
GFP_USER);
if (err)
return ERR_PTR(err);
iter->cur_sk = 0;
iter->end_sk = 0;
sk = tcp_seek_last_pos(seq);
if (!sk)
return NULL; /* Done */
expected = bpf_iter_fill_batch(seq, &sk);
if (likely(iter->end_sk == expected))
goto done;
/* Batch size was still too small. Hold onto the lock while we try
* again with a larger batch to make sure the current bucket's size
* does not change in the meantime.
*/
err = bpf_iter_tcp_realloc_batch(iter, expected, GFP_NOWAIT);
if (err) {
bpf_iter_tcp_unlock_bucket(seq);
return ERR_PTR(err);
}
if (!resized && !bpf_iter_tcp_realloc_batch(iter, expected * 3 / 2,
GFP_USER)) {
resized = true;
goto again;
}
return sk;
expected = bpf_iter_fill_batch(seq, &sk);
WARN_ON_ONCE(iter->end_sk != expected);
done:
bpf_iter_tcp_unlock_bucket(seq);
return iter->batch[0];
}
static void *bpf_iter_tcp_seq_start(struct seq_file *seq, loff_t *pos)