Re: [PATCH 1/2] i2c: designware: Only check the first byte for SMBus block read length

[Sultan Alsawaf <sultan@kerneltoast.com>]

On Mon, Jun 15, 2020 at 12:40:19PM +0300, Andy Shevchenko wrote:
> On Sun, Jun 14, 2020 at 02:02:54PM -0700, Sultan Alsawaf wrote:
> > From: Sultan Alsawaf <sultan@kerneltoast.com>
> > 
> > SMBus block reads can be broken because the read function will just skip
> > over bytes it doesn't like until reaching a byte that conforms to the
> > length restrictions for block reads. This is problematic when it isn't
> > known if the incoming payload is indeed a conforming block read.
> > 
> > According to the SMBus specification, block reads will only send the
> > payload length in the first byte, so we can fix this by only considering
> > the first byte in a sequence for block read length purposes.
> 
> I'm wondering if this overlaps with [1]. AFAIU that one is also makes sure that
> the length is not a garbage.
> 
> [1]: https://lore.kernel.org/linux-i2c/20200613104109.2989-1-mans@mansr.com/T/#u

No overlap. That looks like a similar bug for a different driver. In my case,
the adapter provides native SMBus support, so emulation is never used. This is
clear to see by looking at i2c_transfer_buffer_flags(), which only uses the
master_xfer functions provided by the adapter; it doesn't call the emulation
path at all.

Sultan