netdev - [PATCH v2] packet: fix leakage of tx

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Date:	Fri,  1 Feb 2013 18:21:41 +0100
From:	Phil Sutter <phil.sutter@...rinet.com>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, Johann Baudy <johann.baudy@...-log.net>,
	Daniel Borkmann <dborkman@...hat.com>
Subject: [PATCH v2] packet: fix leakage of tx_ring memory

When releasing a packet socket, the routine packet_set_ring() is reused
to free rings instead of allocating them. But when calling it for the
first time, it fills req->tp_block_nr with the value of rb->pg_vec_len
which in the second invocation makes it bail out since req->tp_block_nr
is greater zero but req->tp_block_size is zero.

This patch solves the problem by passing a zeroed auto-variable to
packet_set_ring() upon each invocation from packet_release().

As far as I can tell, this issue exists even since 69e3c75 (net: TX_RING
and packet mmap), i.e. the original inclusion of TX ring support into
af_packet, but applies only to sockets with both RX and TX ring
allocated, which is probably why this was unnoticed all the time.

Signed-off-by: Phil Sutter <phil.sutter@...rinet.com>
Cc: Johann Baudy <johann.baudy@...-log.net>
Cc: Daniel Borkmann <dborkman@...hat.com>

---
Changes since v1:
- less functions
- more code duplication
---
 net/packet/af_packet.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index a91fd0b..07c9483 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2364,13 +2364,15 @@ static int packet_release(struct socket *sock)

 	packet_flush_mclist(sk);

-	memset(&req_u, 0, sizeof(req_u));
-
-	if (po->rx_ring.pg_vec)
+	if (po->rx_ring.pg_vec) {
+		memset(&req_u, 0, sizeof(req_u));
 		packet_set_ring(sk, &req_u, 1, 0);
+	}

-	if (po->tx_ring.pg_vec)
+	if (po->tx_ring.pg_vec) {
+		memset(&req_u, 0, sizeof(req_u));
 		packet_set_ring(sk, &req_u, 1, 1);
+	}

 	fanout_release(sk);

-- 
1.7.12.3

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