Ocfs2 devel - May 2020 - [PATCH 27/33] sctp: export sctp_setsockopt_bindx

From: David Howells
> Sent: 15 May 2020 16:20
> Christoph Hellwig <hch at lst.de> 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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On Sat, May 16, 2020 at 03:11:40PM +0000, David Laight
wrote:
> From: David Howells
> > Sent: 15 May 2020 16:20
> > Christoph Hellwig <hch at lst.de> 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.
I appreciate your dedication to not publishing the source code to
your kernel module, but Christoph's patch series is actually better.
It's typesafe rather than passing void pointers around.