[PATCH v4 net-next] net: Remove redundant calls of sk_tx_queue_clear().

From: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
To: "David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	Eric Dumazet <edumazet@google.com>
Cc: Amit Shah <aams@amazon.de>,
	Kuniyuki Iwashima <kuniyu@amazon.co.jp>,
	Kuniyuki Iwashima <kuni1840@gmail.com>, <netdev@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	Tariq Toukan <tariqt@mellanox.com>,
	"Boris Pismenny" <borisp@mellanox.com>
Subject: [PATCH v4 net-next] net: Remove redundant calls of sk_tx_queue_clear().
Date: Thu, 28 Jan 2021 21:42:29 +0900	[thread overview]
Message-ID: <20210128124229.78315-1-kuniyu@amazon.co.jp> (raw)

The commit 41b14fb8724d ("net: Do not clear the sock TX queue in
sk_set_socket()") removes sk_tx_queue_clear() from sk_set_socket() and adds
it instead in sk_alloc() and sk_clone_lock() to fix an issue introduced in
the commit e022f0b4a03f ("net: Introduce sk_tx_queue_mapping"). On the
other hand, the original commit had already put sk_tx_queue_clear() in
sk_prot_alloc(): the callee of sk_alloc() and sk_clone_lock(). Thus
sk_tx_queue_clear() is called twice in each path.

If we remove sk_tx_queue_clear() in sk_alloc() and sk_clone_lock(), it
currently works well because (i) sk_tx_queue_mapping is defined between
sk_dontcopy_begin and sk_dontcopy_end, and (ii) sock_copy() called after
sk_prot_alloc() in sk_clone_lock() does not overwrite sk_tx_queue_mapping.
However, if we move sk_tx_queue_mapping out of the no copy area, it
introduces a bug unintentionally.

Therefore, this patch adds a compile-time check to take care of the order
of sock_copy() and sk_tx_queue_clear() and removes sk_tx_queue_clear() from
sk_prot_alloc() so that it does the only allocation and its callers
initialize fields.

v4:
* Fix typo in the changelog (runtime -> compile-time)

v3: https://lore.kernel.org/netdev/20210128021905.57471-1-kuniyu@amazon.co.jp/
* Remove Fixes: tag
* Add BUILD_BUG_ON
* Remove sk_tx_queue_clear() from sk_prot_alloc()
  instead of sk_alloc() and sk_clone_lock()

v2: https://lore.kernel.org/netdev/20210127132215.10842-1-kuniyu@amazon.co.jp/
* Remove Reviewed-by: tag

v1: https://lore.kernel.org/netdev/20210127125018.7059-1-kuniyu@amazon.co.jp/

CC: Tariq Toukan <tariqt@mellanox.com>
CC: Boris Pismenny <borisp@mellanox.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
---
 net/core/sock.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index bbcd4b97eddd..cfbd62a5e079 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1657,6 +1657,16 @@ static void sock_copy(struct sock *nsk, const struct sock *osk)
 #ifdef CONFIG_SECURITY_NETWORK
 	void *sptr = nsk->sk_security;
 #endif
+
+	/* If we move sk_tx_queue_mapping out of the private section,
+	 * we must check if sk_tx_queue_clear() is called after
+	 * sock_copy() in sk_clone_lock().
+	 */
+	BUILD_BUG_ON(offsetof(struct sock, sk_tx_queue_mapping) <
+		     offsetof(struct sock, sk_dontcopy_begin) ||
+		     offsetof(struct sock, sk_tx_queue_mapping) >=
+		     offsetof(struct sock, sk_dontcopy_end));
+
 	memcpy(nsk, osk, offsetof(struct sock, sk_dontcopy_begin));
 
 	memcpy(&nsk->sk_dontcopy_end, &osk->sk_dontcopy_end,
@@ -1690,7 +1700,6 @@ static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,
 
 		if (!try_module_get(prot->owner))
 			goto out_free_sec;
-		sk_tx_queue_clear(sk);
 	}
 
 	return sk;
-- 
2.17.2 (Apple Git-113)

