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@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. 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.
