[PATCH 6.1 069/127] tcp_metrics: fix data-race in tcpm_suck_dst() vs fastopen

Greg Kroah-Hartman
2023-08-09T10:55:41Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit ddf251fa2bc1d3699eec0bae6ed0bc373b8fda79 ]

Whenever tcpm_new() reclaims an old entry, tcpm_suck_dst()
would overwrite data that could be read from tcp_fastopen_cache_get()
or tcp_metrics_fill_info().

We need to acquire fastopen_seqlock to maintain consistency.

For newly allocated objects, tcpm_new() can switch to kzalloc()
to avoid an extra fastopen_seqlock acquisition.

Fixes: 1fe4c481ba63 ("net-tcp: Fast Open client - cookie cache")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230802131500.1478140-7-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/tcp_metrics.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 4fd274836a48f..99ac5efe244d3 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -93,6 +93,7 @@ static struct tcpm_hash_bucket *tcp_metrics_hash __read_mostly;
static unsigned int tcp_metrics_hash_log __read_mostly;

static DEFINE_SPINLOCK(tcp_metrics_lock);
+static DEFINE_SEQLOCK(fastopen_seqlock);

static void tcpm_suck_dst(struct tcp_metrics_block *tm,
const struct dst_entry *dst,
@@ -129,11 +130,13 @@ static void tcpm_suck_dst(struct tcp_metrics_block *tm,
tcp_metric_set(tm, TCP_METRIC_REORDERING,
dst_metric_raw(dst, RTAX_REORDERING));
if (fastopen_clear) {
+ write_seqlock(&fastopen_seqlock);
tm->tcpm_fastopen.mss = 0;
tm->tcpm_fastopen.syn_loss = 0;
tm->tcpm_fastopen.try_exp = 0;
tm->tcpm_fastopen.cookie.exp = false;
tm->tcpm_fastopen.cookie.len = 0;
+ write_sequnlock(&fastopen_seqlock);
}
}

@@ -194,7 +197,7 @@ static struct tcp_metrics_block *tcpm_new(struct dst_entry *dst,
}
tm = oldest;
} else {
- tm = kmalloc(sizeof(*tm), GFP_ATOMIC);
+ tm = kzalloc(sizeof(*tm), GFP_ATOMIC);
if (!tm)
goto out_unlock;
}
@@ -204,7 +207,7 @@ static struct tcp_metrics_block *tcpm_new(struct dst_entry *dst,
tm->tcpm_saddr = *saddr;
tm->tcpm_daddr = *daddr;

- tcpm_suck_dst(tm, dst, true);
+ tcpm_suck_dst(tm, dst, reclaim);

if (likely(!reclaim)) {
tm->tcpm_next = tcp_metrics_hash[hash].chain;
@@ -556,8 +559,6 @@ bool tcp_peer_is_proven(struct request_sock *req, struct dst_entry *dst)
return ret;
}

-static DEFINE_SEQLOCK(fastopen_seqlock);
-
void tcp_fastopen_cache_get(struct sock *sk, u16 *mss,
struct tcp_fastopen_cookie *cookie)
{
--
2.40.1