IB/uverbs: Get rid of null_obj_type

If the method fails after calling rdma_explicit_destroy (eg if
copy_to_user faults) then it will trigger a kernel oops:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD 800000000548d067 P4D 800000000548d067 PUD 54a0067 PMD 0
SMP PTI
CPU: 0 PID: 359 Comm: ibv_rc_pingpong Not tainted 4.18.0-rc1+ #28
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
RIP: 0010:          (null)
Code: Bad RIP value.
RSP: 0018:ffffc900001a3bf0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88000603bd00 RCX: 0000000000000003
RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffff88000603bd00
RBP: 0000000000000001 R08: ffffc900001a3cf8 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffc900001a3cf0
R13: 0000000000000000 R14: ffffc900001a3cf0 R15: 0000000000000000
FS:  00007fb00dda8700(0000) GS:ffff880007c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000000548e004 CR4: 00000000003606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 ? rdma_lookup_put_uobject+0x22/0x50 [ib_uverbs]
 ? uverbs_finalize_object+0x3b/0x60 [ib_uverbs]
 ? uverbs_finalize_attrs+0x128/0x140 [ib_uverbs]
 ? ib_uverbs_cmd_verbs+0x698/0x7c0 [ib_uverbs]
 ? find_held_lock+0x2d/0x90
 ? __might_fault+0x39/0x90
 ? ib_uverbs_ioctl+0x111/0x1f0 [ib_uverbs]
 ? do_vfs_ioctl+0xa0/0x6d0
 ? trace_hardirqs_on_caller+0xed/0x180
 ? _raw_spin_unlock_irq+0x24/0x40
 ? syscall_trace_enter+0x138/0x1d0
 ? ksys_ioctl+0x35/0x60
 ? __x64_sys_ioctl+0x11/0x20
 ? do_syscall_64+0x5b/0x1c0
 ? entry_SYSCALL_64_after_hwframe+0x49/0xbe

This is because the type was replaced with the null_type during explicit
destroy that cannot complete the destruction.

One of the side effects of replacing the type is to make the object
handle totally unreachable - so no other command could attempt to use
it, even though it remains on the uboject list.

We can get the same end result by just fully destroying the object inside
rdma_explicit_destroy and leaving the caller the residual kref for the
uobj with no attached HW object, and no presence in the ubojects list.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>

diff --git a/drivers/infiniband/core/rdma_core.c b/drivers/infiniband/core/rdma_core.c
index 847c6a2..aed7cc2 100644 (file)
--- a/drivers/infiniband/core/rdma_core.c
+++ b/drivers/infiniband/core/rdma_core.c
@@ -439,12 +439,17 @@ static int __must_check _rdma_remove_commit_uobject(struct ib_uobject *uobj,
        struct ib_uverbs_file *ufile = uobj->ufile;
        int ret;
 
+       if (!uobj->object)
+               return 0;
+
        ret = uobj->type->type_class->remove_commit(uobj, why);
        if (ib_is_destroy_retryable(ret, why, uobj)) {
                /* We couldn't remove the object, so just unlock the uobject */
                atomic_set(&uobj->usecnt, 0);
                uobj->type->type_class->lookup_put(uobj, true);
        } else {
+               uobj->object = NULL;
+
                mutex_lock(&ufile->uobjects_lock);
                list_del(&uobj->list);
                mutex_unlock(&ufile->uobjects_lock);
@@ -459,35 +464,13 @@ static int __must_check _rdma_remove_commit_uobject(struct ib_uobject *uobj,
 int __must_check rdma_remove_commit_uobject(struct ib_uobject *uobj)
 {
        int ret;
-       struct ib_uverbs_file *ufile = uobj->ufile;
 
-       /* put the ref count we took at lookup_get */
-       uverbs_uobject_put(uobj);
-       /* Cleanup is running. Calling this should have been impossible */
-       if (!down_read_trylock(&ufile->cleanup_rwsem)) {
-               WARN(true, "ib_uverbs: Cleanup is running while removing an uobject\n");
-               return 0;
-       }
-       assert_uverbs_usecnt(uobj, true);
-       ret = _rdma_remove_commit_uobject(uobj, RDMA_REMOVE_DESTROY);
-
-       up_read(&ufile->cleanup_rwsem);
+       ret = rdma_explicit_destroy(uobj);
+       /* Pairs with the lookup_get done by the caller */
+       rdma_lookup_put_uobject(uobj, true);
        return ret;
 }
 
-static int null_obj_type_class_remove_commit(struct ib_uobject *uobj,
-                                            enum rdma_remove_reason why)
-{
-       return 0;
-}
-
-static const struct uverbs_obj_type null_obj_type = {
-       .type_class = &((const struct uverbs_obj_type_class){
-                       .remove_commit = null_obj_type_class_remove_commit,
-                       /* be cautious */
-                       .needs_kfree_rcu = true}),
-};
-
 int rdma_explicit_destroy(struct ib_uobject *uobject)
 {
        int ret;
@@ -499,14 +482,8 @@ int rdma_explicit_destroy(struct ib_uobject *uobject)
                return 0;
        }
        assert_uverbs_usecnt(uobject, true);
-       ret = uobject->type->type_class->remove_commit(uobject,
-                                                      RDMA_REMOVE_DESTROY);
-       if (ret)
-               goto out;
-
-       uobject->type = &null_obj_type;
+       ret = _rdma_remove_commit_uobject(uobject, RDMA_REMOVE_DESTROY);
 
-out:
        up_read(&ufile->cleanup_rwsem);
        return ret;
 }