[ Upstream commit 4720f9707c783f642332dee3d56dccaefa850e42 ] Strings from the kernel are guaranteed to be null terminated and ynl_attr_validate() checks for this. But it doesn't check if the string has a len of 0, which would cause problems when trying to access data[len - 1]. Fix this by checking that len is positive. Signed-off-by: David Wei <dw@davidwei.uk> Link: https://patch.msgid.link/20250503043050.861238-1-dw@davidwei.uk Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org>