[PATCH 58/81] packet: fix leakage of tx_ring memory

[Herton Ronaldo Krzesinski]

3.5.7.6 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Phil Sutter <phil.sutter@xxxxxxxxxxxx>

commit 9665d5d62487e8e7b1f546c00e11107155384b9a upstream.

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@xxxxxxxxxxxx>
Cc: Johann Baudy <johann.baudy@xxxxxxxxxxx>
Cc: Daniel Borkmann <dborkman@xxxxxxxxxx>
Acked-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@xxxxxxxxxxxxx>
---
 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 901cffd..02b1ef8 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2450,13 +2450,15 @@ 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);
 
-- 
1.7.9.5

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