[RFC PATCH 0/4] API extension for handling sysctl

[Alexey Gladkov]

On Fri, Apr 22, 2022 at 01:44:50PM -0700, Linus Torvalds wrote:
> On Fri, Apr 22, 2022 at 5:53 AM Alexey Gladkov <legion@xxxxxxxxxx> wrote:
> >
> > Yes, Linus, these changes are not the refactoring you were talking
> > about, but I plan to try to do such a refactoring in the my next
> > patchset.
> 
> Heh. Ok, I'm not saying these patches are pretty, and looking up the
> namespace thing is a bit subtle, but it's certainly prettier than the
> existing odd "create a new ctl_table entry because of field abuse".

As I promised, here is one of the possible options for how to get rid of dynamic
memory allocation.

We can slightly extend the API and thus be able to save data at the time the
file is opened. This will not only eliminate the need to allocate memory, but
also provide access to file struct and f_cred.

I made an RFC because I'm not sure that I did the permissions check for
ipc_sysctl. I also did not change all the places where this API can be applied
to make the patch smaller. As in the case of /proc/sys/kernel/printk where
CAP_SYS_ADMIN is checked[1] for the current process at the time of write.

I made a patchset on top of:

git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git for-next

Because there are my previous changes.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/printk/sysctl.c#n17

--

Alexey Gladkov (4):
  sysctl: API extension for handling sysctl
  sysctl: ipc: Do not use dynamic memory
  sysctl: userns: Do not use dynamic memory
  sysctl: mqueue: Do not use dynamic memory

 fs/proc/proc_sysctl.c          |  71 ++++++++--
 include/linux/ipc_namespace.h  |  35 -----
 include/linux/sysctl.h         |  20 ++-
 include/linux/user_namespace.h |   6 -
 ipc/ipc_sysctl.c               | 236 +++++++++++++++++----------------
 ipc/mq_sysctl.c                | 138 ++++++++++---------
 ipc/mqueue.c                   |   5 -
 ipc/namespace.c                |  10 --
 kernel/ucount.c                | 116 +++++++---------
 kernel/user_namespace.c        |  10 +-
 10 files changed, 323 insertions(+), 324 deletions(-)

-- 
2.33.3