Re: [PATCH net-next v2] genetlink: fix single op policy dump when do is present

[Leon Romanovsky <leon@kernel.org>]

On Wed, Nov 09, 2022 at 10:32:54AM -0800, Jakub Kicinski wrote:
> Jonathan reports crashes when running net-next in Meta's fleet.
> Stats collection uses ethtool -I which does a per-op policy dump
> to check if stats are supported. We don't initialize the dumpit
> information if doit succeeds due to evaluation short-circuiting.
> 
> The crash may look like this:
> 
>    BUG: kernel NULL pointer dereference, address: 0000000000000cc0
>    RIP: 0010:netlink_policy_dump_add_policy+0x174/0x2a0
>      ctrl_dumppolicy_start+0x19f/0x2f0
>      genl_start+0xe7/0x140
> 
> Or we may trigger a warning:
> 
>    WARNING: CPU: 1 PID: 785 at net/netlink/policy.c:87 netlink_policy_dump_get_policy_idx+0x79/0x80
>    RIP: 0010:netlink_policy_dump_get_policy_idx+0x79/0x80
>      ctrl_dumppolicy_put_op+0x214/0x360
> 
> depending on what garbage we pick up from the stack.
> 
> Reported-by: Jonathan Lemon <bsd@meta.com>
> Fixes: 26588edbef60 ("genetlink: support split policies in ctrl_dumppolicy_put_op()")
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> CC: jacob.e.keller@intel.com
> CC: leon@kernel.org
> 
> v2:
>  - add a helper instead of doing magic sums
>  - improve title
> v1: https://lore.kernel.org/all/20221108204041.330172-1-kuba@kernel.org/
> ---
>  net/netlink/genetlink.c | 30 +++++++++++++++++++++---------
>  1 file changed, 21 insertions(+), 9 deletions(-)
> 

Thanks,
Tested-by: Leon Romanovsky <leonro@nvidia.com>