Re: [PATCH v8 0/5] ipc: IPCMNI limit check for *mni & increase that limit

[Davidlohr Bueso <dave@stgolabs.net>]

On Mon, 18 Jun 2018, Waiman Long wrote:

>v7->v8:
> - Remove the __read_mostly tag for ipc_mni and related variables as their
>   accesses are not really in performance critical path.
> - Add a new ipcmni_compat sysctl parameter that can be set to restore old
>   range check behavior if desired.
>
>v6->v7:
> - Drop the range clamping code and just return error instead for now
>   until there is user request for clamping support.
> - Fix compilation error when CONFIG_SYSVIPC_SYSCTL isn't defined.
>
>v5->v6:
> - Consolidate the 3 ctl_table flags into 2.
> - Make similar changes to proc_doulongvec_minmax() and its associates
>   to complete the clamping change.
> - Remove the sysctl registration failure test patch for now for later
>   consideration.
> - Add extra braces to patch 1 to reduce code diff in a later patch.
>
>v4->v5:
> - Revert the flags back to 16-bit so that there will be no change to
>   the size of ctl_table.
> - Enhance the sysctl_check_flags() as requested by Luis to perform more
>   checks to spot incorrect ctl_table entries.
> - Change the sysctl selftest to use dummy sysctls instead of production
>   ones & enhance it to do more checks.
> - Add one more sysctl selftest for registration failure.
> - Add 2 ipc patches to add an extended mode to increase IPCMNI from
>   32k to 2M.
> - Miscellaneous change to incorporate feedback comments from
>   reviewers.
>
>v3->v4:
> - Remove v3 patches 1 & 2 as they have been merged into the mm tree.
> - Change flags from uint16_t to unsigned int.
> - Remove CTL_FLAGS_OOR_WARNED and use pr_warn_ratelimited() instead.
> - Simplify the warning message code.
> - Add a new patch to fail the ctl_table registration with invalid flag.
> - Add a test case for range clamping in sysctl selftest.
>
>v2->v3:
> - Fix kdoc comment errors.
> - Incorporate comments and suggestions from Luis R. Rodriguez.
> - Add a patch to fix a typo error in fs/proc/proc_sysctl.c.
>
>v1->v2:
> - Add kdoc comments to the do_proc_do{u}intvec_minmax_conv_param
>   structures.
> - Add a new flags field to the ctl_table structure for specifying
>   whether range clamping should be activated instead of adding new
>   sysctl parameter handlers.
> - Clamp the semmni value embedded in the multi-values sem parameter.
>
>v5 patch: https://lkml.org/lkml/2018/3/16/1106
>v6 patch: https://lkml.org/lkml/2018/4/27/1094
>v7 patch: https://lkml.org/lkml/2018/5/7/666
>
>The sysctl parameters msgmni, shmmni and semmni have an inherent limit
>of IPC_MNI (32k). However, users may not be aware of that because they
>can write a value much higher than that without getting any error or
>notification. Reading the parameters back will show the newly written
>values which are not real.
>
>The real IPCMNI limit is now enforced to make sure that users won't
>put in an unrealistic value. The first 2 patches enforce the limits.
>
>There are also users out there requesting increase in the IPCMNI value.
>The last 2 patches attempt to do that by using a boot kernel parameter
>"ipcmni_extend" to increase the IPCMNI limit from 32k to 2M if the users
>really want the extended value.
>
>Enforcing the range limit check may cause some existing applications to break
>if they unwittingly set a value higher than 32k. To allow system administrators
>to work around this issue, a new ipcmni_compat sysctl parameter can now be set
>to restore the old behavior. This compatibility mode can only be set if the
>ipcmni_extend boot parameter is not specified. Patch 5 implements this new
>sysctl parameter.
>
>Waiman Long (5):
>  ipc: IPCMNI limit check for msgmni and shmmni
>  ipc: IPCMNI limit check for semmni

I've reviewed the first two which look good and are actual immediate fixes
to the bogus user input. I haven't gotten around yet the rest of the patches
but are at least a bit more controversial than the first two. As such, could
patch 1 and 2 be picked up once the merge window closes, for v4.20? Although
-stable might want in, this situation is quite historic, so it's not that
urgent.

Thanks,
Davidlohr

>  ipc: Allow boot time extension of IPCMNI from 32k to 2M
>  ipc: Conserve sequence numbers in extended IPCMNI mode
>  ipc: Add a new ipcmni_compat sysctl to fall back to old behavior
>
> Documentation/admin-guide/kernel-parameters.txt |  3 +
> Documentation/sysctl/kernel.txt                 | 15 +++++
> include/linux/ipc_namespace.h                   |  1 +
> ipc/ipc_sysctl.c                                | 78 ++++++++++++++++++++++++-
> ipc/util.c                                      | 41 ++++++++-----
> ipc/util.h                                      | 50 +++++++++++++---
> 6 files changed, 164 insertions(+), 24 deletions(-)
>
>-- 
>1.8.3.1
>