[PATCH 4.14 17/31] cifs: fix potential use-after-free in cifs_echo_request()

From: Greg Kroah-Hartman
Date: Thu Dec 10 2020 - 13:29:12 EST


From: Paulo Alcantara <pc@xxxxxx>

commit 212253367dc7b49ed3fc194ce71b0992eacaecf2 upstream.

This patch fixes a potential use-after-free bug in
cifs_echo_request().

For instance,

thread 1
--------
cifs_demultiplex_thread()
clean_demultiplex_info()
kfree(server)

thread 2 (workqueue)
--------
apic_timer_interrupt()
smp_apic_timer_interrupt()
irq_exit()
__do_softirq()
run_timer_softirq()
call_timer_fn()
cifs_echo_request() <- use-after-free in server ptr

Signed-off-by: Paulo Alcantara (SUSE) <pc@xxxxxx>
CC: Stable <stable@xxxxxxxxxxxxxxx>
Reviewed-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/cifs/connect.c | 2 ++
1 file changed, 2 insertions(+)

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -756,6 +756,8 @@ static void clean_demultiplex_info(struc
list_del_init(&server->tcp_ses_list);
spin_unlock(&cifs_tcp_ses_lock);

+ cancel_delayed_work_sync(&server->echo);
+
spin_lock(&GlobalMid_Lock);
server->tcpStatus = CifsExiting;
spin_unlock(&GlobalMid_Lock);