HID: bpf: actually free hdev memory after attaching a HID-BPF program

Turns out that I got my reference counts wrong and each successful
bus_find_device() actually calls get_device(), and we need to manually
call put_device().

Ensure each bus_find_device() gets a matching put_device() when releasing
the bpf programs and fix all the error paths.

Cc: <[email protected]>
Fixes: f5c27da ("HID: initial BPF implementation")
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Benjamin Tissoires <[email protected]>

Author: Benjamin Tissoires

drivers/hid/bpf/hid_bpf_dispatch.c

@@ -292,7 +292,7 @@ hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags)
 	struct hid_device *hdev;
 	struct bpf_prog *prog;
 	struct device *dev;
-	int fd;
+	int err, fd;
 
 	if (!hid_bpf_ops)
 		return -EINVAL;
@@ -311,14 +311,24 @@ hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags)
 	 * on errors or when it'll be detached
 	 */
 	prog = bpf_prog_get(prog_fd);
-	if (IS_ERR(prog))
-		return PTR_ERR(prog);
+	if (IS_ERR(prog)) {
+		err = PTR_ERR(prog);
+		goto out_dev_put;
+	}
 
 	fd = do_hid_bpf_attach_prog(hdev, prog_fd, prog, flags);
-	if (fd < 0)
-		bpf_prog_put(prog);
+	if (fd < 0) {
+		err = fd;
+		goto out_prog_put;
+	}
 
 	return fd;
+
+ out_prog_put:
+	bpf_prog_put(prog);
+ out_dev_put:
+	put_device(dev);
+	return err;
 }
 
 /**
@@ -345,8 +355,10 @@ hid_bpf_allocate_context(unsigned int hid_id)
 	hdev = to_hid_device(dev);
 
 	ctx_kern = kzalloc(sizeof(*ctx_kern), GFP_KERNEL);
-	if (!ctx_kern)
+	if (!ctx_kern) {
+		put_device(dev);
 		return NULL;
+	}
 
 	ctx_kern->ctx.hid = hdev;
 
@@ -363,10 +375,15 @@ noinline void
 hid_bpf_release_context(struct hid_bpf_ctx *ctx)
 {
 	struct hid_bpf_ctx_kern *ctx_kern;
+	struct hid_device *hid;
 
 	ctx_kern = container_of(ctx, struct hid_bpf_ctx_kern, ctx);
+	hid = (struct hid_device *)ctx_kern->ctx.hid; /* ignore const */
 
 	kfree(ctx_kern);
+
+	/* get_device() is called by bus_find_device() */
+	put_device(&hid->dev);
 }
 
 /**

drivers/hid/bpf/hid_bpf_jmp_table.c

@@ -196,6 +196,7 @@ static void __hid_bpf_do_release_prog(int map_fd, unsigned int idx)
 static void hid_bpf_release_progs(struct work_struct *work)
 {
 	int i, j, n, map_fd = -1;
+	bool hdev_destroyed;
 
 	if (!jmp_table.map)
 		return;
@@ -220,6 +221,12 @@ static void hid_bpf_release_progs(struct work_struct *work)
 		if (entry->hdev) {
 			hdev = entry->hdev;
 			type = entry->type;
+			/*
+			 * hdev is still valid, even if we are called after hid_destroy_device():
+			 * when hid_bpf_attach() gets called, it takes a ref on the dev through
+			 * bus_find_device()
+			 */
+			hdev_destroyed = hdev->bpf.destroyed;
 
 			hid_bpf_populate_hdev(hdev, type);
 
@@ -232,12 +239,19 @@ static void hid_bpf_release_progs(struct work_struct *work)
 				if (test_bit(next->idx, jmp_table.enabled))
 					continue;
 
-				if (next->hdev == hdev && next->type == type)
+				if (next->hdev == hdev && next->type == type) {
+					/*
+					 * clear the hdev reference and decrement the device ref
+					 * that was taken during bus_find_device() while calling
+					 * hid_bpf_attach()
+					 */
 					next->hdev = NULL;
+					put_device(&hdev->dev);
+				}
 			}
 
-			/* if type was rdesc fixup, reconnect device */
-			if (type == HID_BPF_PROG_TYPE_RDESC_FIXUP)
+			/* if type was rdesc fixup and the device is not gone, reconnect device */
+			if (type == HID_BPF_PROG_TYPE_RDESC_FIXUP && !hdev_destroyed)
 				hid_bpf_reconnect(hdev);
 		}
 	}