From: David Howells
> Sent: 15 May 2020 16:20
> Christoph Hellwig <hch@xxxxxx> wrote:
>
> > > The advantage on using kernel_setsockopt here is that sctp module will
> > > only be loaded if dlm actually creates a SCTP socket. With this
> > > change, sctp will be loaded on setups that may not be actually using
> > > it. It's a quite big module and might expose the system.
> >
> > True. Not that the intent is to kill kernel space callers of setsockopt,
> > as I plan to remove the set_fs address space override used for it.
>
> For getsockopt, does it make sense to have the core kernel load optval/optlen
> into a buffer before calling the protocol driver? Then the driver need not
> see the userspace pointer at all.
>
> Similar could be done for setsockopt - allocate a buffer of the size requested
> by the user inside the kernel and pass it into the driver, then copy the data
> back afterwards.
Yes, it also simplifies all the compat code.
And there is a BPF test in setsockopt that also wants to
pass on a kernel buffer.
I'm willing to sit and write the patch.
Quoting from a post I made later on Friday.
Basically:
This patch sequence (to be written) does the following:
Patch 1: Change __sys_setsockopt() to allocate a kernel buffer,
copy the data into it then call set_fs(KERNEL_DS).
An on-stack buffer (say 64 bytes) will be used for
small transfers.
Patch 2: The same for __sys_getsockopt().
Patch 3: Compat setsockopt.
Patch 4: Compat getsockopt.
Patch 5: Remove the user copies from the global socket options code.
Patches 6 to n-1; Remove the user copies from the per-protocol code.
Patch n: Remove the set_fs(KERNEL_DS) from the entry points.
This should be bisectable.
David
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