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63 lines
2.5 KiB
Diff
63 lines
2.5 KiB
Diff
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From 1f5495019fce5680d54f94204500ee59d43fa15a Mon Sep 17 00:00:00 2001
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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
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Date: Wed, 9 Sep 2020 13:58:15 +0200
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Subject: [PATCH 116/124] wireguard: peerlookup: take lock before checking hash
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in replace operation
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commit 6147f7b1e90ff09bd52afc8b9206a7fcd133daf7 upstream.
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Eric's suggested fix for the previous commit's mentioned race condition
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was to simply take the table->lock in wg_index_hashtable_replace(). The
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table->lock of the hash table is supposed to protect the bucket heads,
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not the entires, but actually, since all the mutator functions are
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already taking it, it makes sense to take it too for the test to
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hlist_unhashed, as a defense in depth measure, so that it no longer
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races with deletions, regardless of what other locks are protecting
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individual entries. This is sensible from a performance perspective
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because, as Eric pointed out, the case of being unhashed is already the
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unlikely case, so this won't add common contention. And comparing
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instructions, this basically doesn't make much of a difference other
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than pushing and popping %r13, used by the new `bool ret`. More
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generally, I like the idea of locking consistency across table mutator
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functions, and this might let me rest slightly easier at night.
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Suggested-by: Eric Dumazet <edumazet@google.com>
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Link: https://lore.kernel.org/wireguard/20200908145911.4090480-1-edumazet@google.com/
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Fixes: e7096c131e51 ("net: WireGuard secure network tunnel")
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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---
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drivers/net/wireguard/peerlookup.c | 11 ++++++++---
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1 file changed, 8 insertions(+), 3 deletions(-)
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--- a/drivers/net/wireguard/peerlookup.c
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+++ b/drivers/net/wireguard/peerlookup.c
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@@ -167,9 +167,13 @@ bool wg_index_hashtable_replace(struct i
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struct index_hashtable_entry *old,
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struct index_hashtable_entry *new)
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{
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- if (unlikely(hlist_unhashed(&old->index_hash)))
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- return false;
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+ bool ret;
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+
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spin_lock_bh(&table->lock);
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+ ret = !hlist_unhashed(&old->index_hash);
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+ if (unlikely(!ret))
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+ goto out;
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+
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new->index = old->index;
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hlist_replace_rcu(&old->index_hash, &new->index_hash);
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@@ -180,8 +184,9 @@ bool wg_index_hashtable_replace(struct i
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* simply gets dropped, which isn't terrible.
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*/
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INIT_HLIST_NODE(&old->index_hash);
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+out:
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spin_unlock_bh(&table->lock);
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- return true;
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+ return ret;
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}
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void wg_index_hashtable_remove(struct index_hashtable *table,
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