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From: Martin KaFai Lau <kafai@fb.com>
To: <bpf@vger.kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Eric Dumazet <edumazet@google.com>, <kernel-team@fb.com>,
	Neal Cardwell <ncardwell@google.com>, <netdev@vger.kernel.org>,
	Yonghong Song <yhs@fb.com>, Yuchung Cheng <ycheng@google.com>
Subject: [PATCH v2 bpf-next 1/8] tcp: seq_file: Avoid skipping sk during tcp_seek_last_pos
Date: Thu, 1 Jul 2021 13:05:41 -0700	[thread overview]
Message-ID: <20210701200541.1033917-1-kafai@fb.com> (raw)
In-Reply-To: <20210701200535.1033513-1-kafai@fb.com>

st->bucket stores the current bucket number.
st->offset stores the offset within this bucket that is the sk to be
seq_show().  Thus, st->offset only makes sense within the same
st->bucket.

These two variables are an optimization for the common no-lseek case.
When resuming the seq_file iteration (i.e. seq_start()),
tcp_seek_last_pos() tries to continue from the st->offset
at bucket st->bucket.

However, it is possible that the bucket pointed by st->bucket
has changed and st->offset may end up skipping the whole st->bucket
without finding a sk.  In this case, tcp_seek_last_pos() currently
continues to satisfy the offset condition in the next (and incorrect)
bucket.  Instead, regardless of the offset value, the first sk of the
next bucket should be returned.  Thus, "bucket == st->bucket" check is
added to tcp_seek_last_pos().

The chance of hitting this is small and the issue is a decade old,
so targeting for the next tree.

Fixes: a8b690f98baf ("tcp: Fix slowness in read /proc/net/tcp")
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
 net/ipv4/tcp_ipv4.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index e66ad6bfe808..26b7b2056585 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2451,6 +2451,7 @@ static void *tcp_get_idx(struct seq_file *seq, loff_t pos)
 static void *tcp_seek_last_pos(struct seq_file *seq)
 {
 	struct tcp_iter_state *st = seq->private;
+	int bucket = st->bucket;
 	int offset = st->offset;
 	int orig_num = st->num;
 	void *rc = NULL;
@@ -2461,7 +2462,7 @@ static void *tcp_seek_last_pos(struct seq_file *seq)
 			break;
 		st->state = TCP_SEQ_STATE_LISTENING;
 		rc = listening_get_next(seq, NULL);
-		while (offset-- && rc)
+		while (offset-- && rc && bucket == st->bucket)
 			rc = listening_get_next(seq, rc);
 		if (rc)
 			break;
@@ -2472,7 +2473,7 @@ static void *tcp_seek_last_pos(struct seq_file *seq)
 		if (st->bucket > tcp_hashinfo.ehash_mask)
 			break;
 		rc = established_get_first(seq);
-		while (offset-- && rc)
+		while (offset-- && rc && bucket == st->bucket)
 			rc = established_get_next(seq, rc);
 	}
 
-- 
2.30.2


  reply	other threads:[~2021-07-01 20:05 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-01 20:05 [PATCH v2 bpf-next 0/8] bpf: Allow bpf tcp iter to do bpf_(get|set)sockopt Martin KaFai Lau
2021-07-01 20:05 ` Martin KaFai Lau [this message]
2021-07-22 14:16   ` [PATCH v2 bpf-next 1/8] tcp: seq_file: Avoid skipping sk during tcp_seek_last_pos Kuniyuki Iwashima
2021-07-22 15:08     ` Kuniyuki Iwashima
2021-07-22 21:42       ` Martin KaFai Lau
2021-07-22 22:06         ` Kuniyuki Iwashima
2021-07-01 20:05 ` [PATCH v2 bpf-next 2/8] tcp: seq_file: Refactor net and family matching Martin KaFai Lau
2021-07-01 20:05 ` [PATCH v2 bpf-next 3/8] bpf: tcp: seq_file: Remove bpf_seq_afinfo from tcp_iter_state Martin KaFai Lau
2021-07-01 20:06 ` [PATCH v2 bpf-next 4/8] tcp: seq_file: Add listening_get_first() Martin KaFai Lau
2021-07-01 20:06 ` [PATCH v2 bpf-next 5/8] tcp: seq_file: Replace listening_hash with lhash2 Martin KaFai Lau
2021-07-01 20:06 ` [PATCH v2 bpf-next 6/8] bpf: tcp: bpf iter batching and lock_sock Martin KaFai Lau
2021-07-01 20:06 ` [PATCH v2 bpf-next 7/8] bpf: tcp: Support bpf_(get|set)sockopt in bpf tcp iter Martin KaFai Lau
2021-07-01 20:06 ` [PATCH v2 bpf-next 8/8] bpf: selftest: Test batching and " Martin KaFai Lau
2021-07-02 10:50 ` [PATCH v2 bpf-next 0/8] bpf: Allow bpf tcp iter to do bpf_(get|set)sockopt David Laight
2021-07-06 15:44   ` Martin KaFai Lau
2021-07-15  1:29 ` Alexei Starovoitov
2021-07-20 18:05   ` Alexei Starovoitov
2021-07-20 18:42     ` Eric Dumazet
2021-07-22 13:25 ` Eric Dumazet
2021-07-22 21:01   ` Martin KaFai Lau
2021-07-22 14:53 ` Kuniyuki Iwashima

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