[PATCH 5.4 20/54] cifs: fix potential use-after-free in cifs_echo_request()

Greg Kroah-Hartman
2020-12-10T16:55:47Z

From: Paulo Alcantara <pc@cjr.nz>

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@cjr.nz>
CC: Stable <stable@vger.kernel.org>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -975,6 +975,8 @@ 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);