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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Jakub Sitnicki <jakub@cloudflare.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>
Subject: [PATCH 5.4 23/96] bpf, sockhash: Synchronize_rcu before freeing map
Date:   Thu, 13 Feb 2020 07:20:30 -0800
Message-Id: <20200213151848.153137952@linuxfoundation.org>
In-Reply-To: <20200213151839.156309910@linuxfoundation.org>
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From: Jakub Sitnicki <jakub@cloudflare.com>

commit 0b2dc83906cf1e694e48003eae5df8fa63f76fd9 upstream.

We need to have a synchronize_rcu before free'ing the sockhash because any
outstanding psock references will have a pointer to the map and when they
use it, this could trigger a use after free.

This is a sister fix for sockhash, following commit 2bb90e5cc90e ("bpf:
sockmap, synchronize_rcu before free'ing map") which addressed sockmap,
which comes from a manual audit.

Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200206111652.694507-3-jakub@cloudflare.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/core/sock_map.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -250,6 +250,7 @@ static void sock_map_free(struct bpf_map
 	}
 	raw_spin_unlock_bh(&stab->lock);
 
+	/* wait for psock readers accessing its map link */
 	synchronize_rcu();
 
 	bpf_map_area_free(stab->sks);
@@ -873,6 +874,9 @@ static void sock_hash_free(struct bpf_ma
 		raw_spin_unlock_bh(&bucket->lock);
 	}
 
+	/* wait for psock readers accessing its map link */
+	synchronize_rcu();
+
 	bpf_map_area_free(htab->buckets);
 	kfree(htab);
 }