misc: sgi-gru: fix use-after-free error in gru_set_context_option, gru_fault and gru_handle_user_call_os

In some bad situation, the gts may be freed gru_check_chiplet_assignment.
The call chain can be gru_unload_context->gru_free_gru_context->gts_drop
and kfree finally. However, the caller didn't know if the gts is freed
or not and use it afterwards. This will trigger a Use after Free bug.

Fix it by introducing a return value to see if it's in error path or not.
Free the gts in caller if gru_check_chiplet_assignment check failed.

Fixes: 55484c45dbec ("gru: allow users to specify gru chiplet 2")
Signed-off-by: Zheng Wang <[e-mail]>
Acked-by: Dimitri Sivanich <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/sgi-gru/grufault.c

···
 	if ((cb & (GRU_HANDLE_STRIDE - 1)) || ucbnum >= GRU_NUM_CB)
 		return -EINVAL;
 
+again:
 	gts = gru_find_lock_gts(cb);
 	if (!gts)
 		return -EINVAL;
···
 	if (ucbnum >= gts->ts_cbr_au_count * GRU_CBR_AU_SIZE)
 		goto exit;
 
-	gru_check_context_placement(gts);
+	if (gru_check_context_placement(gts)) {
+		gru_unlock_gts(gts);
+		gru_unload_context(gts, 1);
+		goto again;
+	}
 
 	/*
 	 * CCH may contain stale data if ts_force_cch_reload is set.
···
 		} else {
 			gts->ts_user_blade_id = req.val1;
 			gts->ts_user_chiplet_id = req.val0;
-			gru_check_context_placement(gts);
+			if (gru_check_context_placement(gts)) {
+				gru_unlock_gts(gts);
+				gru_unload_context(gts, 1);
+				return ret;
+			}
 		}
 		break;
 	case sco_gseg_owner:

drivers/misc/sgi-gru/grumain.c

···
  * chiplet. Misassignment can occur if the process migrates to a different
  * blade or if the user changes the selected blade/chiplet.
  */
-void gru_check_context_placement(struct gru_thread_state *gts)
+int gru_check_context_placement(struct gru_thread_state *gts)
 {
 	struct gru_state *gru;
+	int ret = 0;
 
 	/*
 	 * If the current task is the context owner, verify that the
···
 	 * references. Pthread apps use non-owner references to the CBRs.
 	 */
 	gru = gts->ts_gru;
+	/*
+	 * If gru or gts->ts_tgid_owner isn't initialized properly, return
+	 * success to indicate that the caller does not need to unload the
+	 * gru context.The caller is responsible for their inspection and
+	 * reinitialization if needed.
+	 */
 	if (!gru || gts->ts_tgid_owner != current->tgid)
-		return;
+		return ret;
 
 	if (!gru_check_chiplet_assignment(gru, gts)) {
 		STAT(check_context_unload);
-		gru_unload_context(gts, 1);
+		ret = -EINVAL;
 	} else if (gru_retarget_intr(gts)) {
 		STAT(check_context_retarget_intr);
 	}
+
+	return ret;
 }
 
 
···
 	mutex_lock(&gts->ts_ctxlock);
 	preempt_disable();
 
-	gru_check_context_placement(gts);
+	if (gru_check_context_placement(gts)) {
+		preempt_enable();
+		mutex_unlock(&gts->ts_ctxlock);
+		gru_unload_context(gts, 1);
+		return VM_FAULT_NOPAGE;
+	}
 
 	if (!gts->ts_gru) {
 		STAT(load_user_context);

drivers/misc/sgi-gru/grutables.h

···
 extern int gru_user_unload_context(unsigned long arg);
 extern int gru_get_exception_detail(unsigned long arg);
 extern int gru_set_context_option(unsigned long address);
-extern void gru_check_context_placement(struct gru_thread_state *gts);
+extern int gru_check_context_placement(struct gru_thread_state *gts);
 extern int gru_cpu_fault_map_id(void);
 extern struct vm_area_struct *gru_find_vma(unsigned long vaddr);
 extern void gru_flush_all_tlb(struct gru_state *gru);