[PATCH 5.4 06/52] firewire: fix potential uaf in outbound_phy_packet_callback()

[Greg Kroah-Hartman]

From: Chengfeng Ye <cyeaa@xxxxxxxxxxxxxx>

commit b7c81f80246fac44077166f3e07103affe6db8ff upstream.

&e->event and e point to the same address, and &e->event could
be freed in queue_event. So there is a potential uaf issue if
we dereference e after calling queue_event(). Fix this by adding
a temporary variable to maintain e->client in advance, this can
avoid the potential uaf issue.

Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Chengfeng Ye <cyeaa@xxxxxxxxxxxxxx>
Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220409041243.603210-2-o-takashi@xxxxxxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/firewire/core-cdev.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/firewire/core-cdev.c
+++ b/drivers/firewire/core-cdev.c
@@ -1482,6 +1482,7 @@ static void outbound_phy_packet_callback
 {
 	struct outbound_phy_packet_event *e =
 		container_of(packet, struct outbound_phy_packet_event, p);
+	struct client *e_client;
 
 	switch (status) {
 	/* expected: */
@@ -1498,9 +1499,10 @@ static void outbound_phy_packet_callback
 	}
 	e->phy_packet.data[0] = packet->timestamp;
 
+	e_client = e->client;
 	queue_event(e->client, &e->event, &e->phy_packet,
 		    sizeof(e->phy_packet) + e->phy_packet.length, NULL, 0);
-	client_put(e->client);
+	client_put(e_client);
 }
 
 static int ioctl_send_phy_packet(struct client *client, union ioctl_arg *arg)