Re: [RFC PATCH 1/3] mmc: core: validate user input for RPMB block count

[Wolfram Sang <wsa@the-dreams.de>]

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Hi Avri,

thanks for your comments!

> > For RPMB, block count is a non-zero 16 bit wide number. Reject invalid
> Actually this is not what limits the number of rpmb frames to be read,
> As those are not indicated in the block_count field of the rpmb frame,
> But in CMD23.
> While it is true that by eMMCv52 RPMB_SIZE_MULT max value is 0x80,
> Which limits the RPMB are to 16M, or 65535 rpmb frames,
> I don't think that it is up to the host to validate the rpmb frame content - 

I wanted to fix the following issue:

Currently, in to-be-removed mmc_set_blockcount() we have:

	cmd.arg = blockcount & 0x0000FFFF;

So, sending a IOCTL with a value of 65537 will silently(!) produce a
block count of 1. I didn't like this.

I don't have the eMMC specs on this computer but I recall it is defined
somewhere that there are 2 bytes reserved for it in the packet frame?

But yes, standards may be extended, so I am not opposed to fill in
bigger numbers than 16 bit and let the card handle the error.

So you suggest dropping this patch and keep the others, did I get this
right? Would be fine with me.

Regards,

   Wolfram


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