On Mon, Sep 28, 2020 at 09:00:54PM +0300, Dmitry Kasatkin wrote: > But why "we" should allow "discarding" failed part instead of failing > with EFAULT as a whole? Because there might very well be absolutely legitimate users of mount(2) passing it something smaller than 4Kb immediately followed by an unmapped area. What can mount(2) do? It can't go up to the first \0 and stop there, thanks to filesystems (NFS) that want to get struct some_shite filled by userland. It can't require the entire 4Kb from the pointer passed to mount(2) to be mapped and readable, simply because passing it a string literal for e.g. ext4 mount can violate that requirement, not to mention the result of strdup(3)/asprintf(3)/etc. And it can't even tell which semantics to use by looking at the filesystem type - NFS allows both the string and binary structure for options.
