FileSystemInfoHeader is misalligned

[josephlr]

Per the EDK2 source for EFI_FILE_SYSTEM_INFO, our FileSystemInfo struct should have the following layout (as a rust structure):

#[repr(C)]
pub struct FileSystemInfo {
    size: u64,
    read_only: bool,
    volume_size: u64,
    free_space: u64,
    block_size: u32,
    name: [Char16],
}

However, as the uefi-rs code uses separate structs for the header and name components. This causes the name field to be misalligned, and the unsafe pointer arithmetic in the module to be wrong.

The result of this is that using volume_label() field with FileSystemInfo can perform an out of bounds read if the length is empty (unfortunately this is the default for mkfs.fat), and it always returns an incorrect value for the label. Tested and confirmed on qemu-edk2 and a real system.

[HadrienG2]

Thanks for reporting! I expected the header/name split to have no effect on alignment, guess I need to review the C struct layout rules. If it does, then I suspect that can be worked around with judicious use of repr(packed) and padding... but it remains to be seen.

[josephlr]

I manged to get a WIP solution working where the only types are DSTs. However, I think the code would be a lot cleaner if there was a helper trait added that essentially said, "I am a DST and this is my last DST field". Then, each FileProtocolInfo field could simply implement this trait, and the rest of the implementation could be generic.