pppoatm: fix module_put() race

The pppoatm used module_put() during unassignment from vcc with
hope that we have BKL. This assumption is no longer true.

Now owner field in atmvcc is used to move this module_put()
to vcc_destroy_socket().

Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c
index f27a07a3c546..b23c6723e87c 100644
--- a/net/atm/pppoatm.c
+++ b/net/atm/pppoatm.c
@@ -60,6 +60,7 @@ struct pppoatm_vcc {
         struct atm_vcc  *atmvcc;        /* VCC descriptor */
         void (*old_push)(struct atm_vcc *, struct sk_buff *);
         void (*old_pop)(struct atm_vcc *, struct sk_buff *);
+        struct module *old_owner;
                                         /* keep old push/pop for detaching */
         enum pppoatm_encaps encaps;
         atomic_t inflight;
@@ -155,8 +156,6 @@ static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
         ppp_unregister_channel(&pvcc->chan);
         atmvcc->user_back = NULL;
         kfree(pvcc);
-        /* Gee, I hope we have the big kernel lock here... */
-        module_put(THIS_MODULE);
 }
 
 /* Called when an AAL5 PDU comes in */
@@ -165,9 +164,13 @@ static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
         struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
         pr_debug("\n");
         if (skb == NULL) {                      /* VCC was closed */
+                struct module *module;
+
                 pr_debug("removing ATMPPP VCC %p\n", pvcc);
+                module = pvcc->old_owner;
                 pppoatm_unassign_vcc(atmvcc);
                 atmvcc->push(atmvcc, NULL);     /* Pass along bad news */
+                module_put(module);
                 return;
         }
         atm_return(atmvcc, skb->truesize);
@@ -362,6 +365,7 @@ static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
         atomic_set(&pvcc->inflight, NONE_INFLIGHT);
         pvcc->old_push = atmvcc->push;
         pvcc->old_pop = atmvcc->pop;
+        pvcc->old_owner = atmvcc->owner;
         pvcc->encaps = (enum pppoatm_encaps) be.encaps;
         pvcc->chan.private = pvcc;
         pvcc->chan.ops = &pppoatm_ops;
@@ -378,6 +382,7 @@ static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
         atmvcc->push = pppoatm_push;
         atmvcc->pop = pppoatm_pop;
         __module_get(THIS_MODULE);
+        atmvcc->owner = THIS_MODULE;
 
         /* re-process everything received between connection setup and
            backend setup */