Ocfs2 devel - May 2020 - [PATCH 32/33] sctp: add sctp_sock_get_primary_addr

From: Marcelo Ricardo Leitner
> Sent: 13 May 2020 19:03
> 
> On Wed, May 13, 2020 at 08:26:47AM +0200, Christoph Hellwig wrote:
> > Add a helper to directly get the SCTP_PRIMARY_ADDR sockopt from kernel
> > space without going through a fake uaccess.
> 
> Same comment as on the other dlm/sctp patch.
Wouldn't it be best to write sctp_[gs]etsockotp() that
use a kernel buffer and then implement the user-space
calls using a wrapper that does the copies to an on-stack
(or malloced if big) buffer.

That will also simplify the code be removing all the copies
and -EFAULT returns.
Only the size checks will be needed and the code can assume
the buffer is at least the size of the on-stack buffer.

Our SCTP code uses SO_REUSADDR, SCTP_EVENTS, SCTP_NODELAY,
SCTP_STATUS, SCTP_INITMSG, IPV6_ONLY, SCTP_SOCKOPT_BINDX_ADD
and SO_LINGER.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)

From: David Laight
> Sent: 14 May 2020 10:51
> From: Marcelo Ricardo Leitner
> > Sent: 13 May 2020 19:03
> >
> > On Wed, May 13, 2020 at 08:26:47AM +0200, Christoph Hellwig wrote:
> > > Add a helper to directly get the SCTP_PRIMARY_ADDR sockopt from
kernel
> > > space without going through a fake uaccess.
> >
> > Same comment as on the other dlm/sctp patch.
> 
> Wouldn't it be best to write sctp_[gs]etsockotp() that
> use a kernel buffer and then implement the user-space
> calls using a wrapper that does the copies to an on-stack
> (or malloced if big) buffer.
Actually looking at __sys_setsockopt() it calls
BPF_CGROUP_RUN_PROG_SETSOCKOPT() which (by the look of it)
can copy the user buffer into malloc()ed memory and
cause set_fs(KERNEL_DS) be called.

The only way to get rid of that set_fs() is to always
have the buffer in kernel memory when the underlying
setsockopt() code is called.

The comment above __sys_[sg]etsockopt() about not knowing
the length is just wrong.
It probably applied to getsockopt() in the dim and distant
past before it was made read-update.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)