packet: fix leakage of tx_ring memory

[ Upstream commit 9665d5d62487e8e7b1f546c00e11107155384b9a ]

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@viprinet.com>
Cc: Johann Baudy <johann.baudy@gnu-log.net>
Cc: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 1ab5a0203ac..4058afe0c5a 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1349,13 +1349,15 @@ static int packet_release(struct socket *sock)
 
         packet_flush_mclist(sk);
 
-        memset(&req, 0, sizeof(req));
-
-        if (po->rx_ring.pg_vec)
+        if (po->rx_ring.pg_vec) {
+                memset(&req, 0, sizeof(req));
                 packet_set_ring(sk, &req, 1, 0);
+        }
 
-        if (po->tx_ring.pg_vec)
+        if (po->tx_ring.pg_vec) {
+                memset(&req, 0, sizeof(req));
                 packet_set_ring(sk, &req, 1, 1);
+        }
 
         synchronize_net();
         /*