slcan: Fix double-free on slcan_open() error path

Commit 9ebd796e2400 ("can: slcan: Fix use-after-free Read in
slcan_open") was incorrectly backported to 4.4 and 4.9 stable
branches.

Since they do not have commit cf124db566e6 ("net: Fix inconsistent
teardown and release of private netdev state."), the destructor
function slc_free_netdev() is already responsible for calling
free_netdev() and slcan_open() must not call both of them.

yangerkun previously fixed the same bug in slip.

Fixes: ce624b2089ea ("can: slcan: Fix use-after-free Read in slcan_open") # 4.4
Fixes: f59604a80fa4 ("slcan: not call free_netdev before rtnl_unlock ...") # 4.4
Fixes: 56635a1e6ffb ("can: slcan: Fix use-after-free Read in slcan_open") # 4.9
Fixes: a1c9b23142ac ("slcan: not call free_netdev before rtnl_unlock ...") # 4.9
Cc: yangerkun <yangerkun@huawei.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/can/slcan.c b/drivers/net/can/slcan.c
index d0435c7631ff9eb5d594e9b244b5673cccfc2dbb..9c938f9892b2794c43f2499769ece7e4a480821a 100644 (file)
--- a/drivers/net/can/slcan.c
+++ b/drivers/net/can/slcan.c
@@ -618,10 +618,9 @@ err_free_chan:
        sl->tty = NULL;
        tty->disc_data = NULL;
        clear_bit(SLF_INUSE, &sl->flags);
-       slc_free_netdev(sl->dev);
        /* do not call free_netdev before rtnl_unlock */
        rtnl_unlock();
-       free_netdev(sl->dev);
+       slc_free_netdev(sl->dev);
        return err;
 
 err_exit: