Since the actual_length calculation is performed unsigned, packets
shorter than 7 bytes (e.g. packets without data or otherwise truncated)
or non-received packets ("zero" bytes) can cause buffer overflow.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=214437
Fixes: 42337b9d4d958("HID: add driver for U2F Zero built-in LED and RNG")
Signed-off-by: Andrej Shadura <redacted>
---
 drivers/hid/hid-u2fzero.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
index 95e0807878c7..d70cd3d7f583 100644
--- a/drivers/hid/hid-u2fzero.c
+++ b/drivers/hid/hid-u2fzero.c

@@ -198,7 +198,9 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
 	}
 
 	ret = u2fzero_recv(dev, &req, &resp);
-	if (ret < 0)
+
+	/* ignore errors or packets without data */
+	if (ret < offsetof(struct u2f_hid_msg, init.data))
 		return 0;