drivers/virt/fsl_hypervisor.c: dereferencing error pointers in ioctl

BugLink: https://bugs.launchpad.net/bugs/1830176

commit c8ea3663 upstream.

strndup_user() returns error pointers on error, and then in the error
handling we pass the error pointers to kfree().  It will cause an Oops.

Link: http://lkml.kernel.org/r/20181218082003.GD32567@kadam
Fixes: 6db71994 ("drivers/virt: introduce Freescale hypervisor management driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Timur Tabi <timur@freescale.com>
Cc: Mihai Caraman <mihai.caraman@freescale.com>
Cc: Kumar Gala <galak@kernel.crashing.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/virt/fsl_hypervisor.c

@@ -335,8 +335,8 @@ static long ioctl_dtprop(struct fsl_hv_ioctl_prop __user *p, int set)
 	struct fsl_hv_ioctl_prop param;
 	char __user *upath, *upropname;
 	void __user *upropval;
-	char *path = NULL, *propname = NULL;
-	void *propval = NULL;
+	char *path, *propname;
+	void *propval;
 	int ret = 0;
 
 	/* Get the parameters from the user. */
@@ -348,32 +348,30 @@ static long ioctl_dtprop(struct fsl_hv_ioctl_prop __user *p, int set)
 	upropval = (void __user *)(uintptr_t)param.propval;
 
 	path = strndup_user(upath, FH_DTPROP_MAX_PATHLEN);
-	if (IS_ERR(path)) {
-		ret = PTR_ERR(path);
-		goto out;
-	}
+	if (IS_ERR(path))
+		return PTR_ERR(path);
 
 	propname = strndup_user(upropname, FH_DTPROP_MAX_PATHLEN);
 	if (IS_ERR(propname)) {
 		ret = PTR_ERR(propname);
-		goto out;
+		goto err_free_path;
 	}
 
 	if (param.proplen > FH_DTPROP_MAX_PROPLEN) {
 		ret = -EINVAL;
-		goto out;
+		goto err_free_propname;
 	}
 
 	propval = kmalloc(param.proplen, GFP_KERNEL);
 	if (!propval) {
 		ret = -ENOMEM;
-		goto out;
+		goto err_free_propname;
 	}
 
 	if (set) {
 		if (copy_from_user(propval, upropval, param.proplen)) {
 			ret = -EFAULT;
-			goto out;
+			goto err_free_propval;
 		}
 
 		param.ret = fh_partition_set_dtprop(param.handle,
@@ -392,7 +390,7 @@ static long ioctl_dtprop(struct fsl_hv_ioctl_prop __user *p, int set)
 			if (copy_to_user(upropval, propval, param.proplen) ||
 			    put_user(param.proplen, &p->proplen)) {
 				ret = -EFAULT;
-				goto out;
+				goto err_free_propval;
 			}
 		}
 	}
@@ -400,10 +398,12 @@ static long ioctl_dtprop(struct fsl_hv_ioctl_prop __user *p, int set)
 	if (put_user(param.ret, &p->ret))
 		ret = -EFAULT;
 
-out:
-	kfree(path);
+err_free_propval:
 	kfree(propval);
+err_free_propname:
 	kfree(propname);
+err_free_path:
+	kfree(path);
 
 	return ret;
 }