On Thu, Feb 29, 2024 at 11:37:28AM +0300, Vasiliy Kovalev wrote:
[...]
This patch fixes another problem, but a similar one, since the sequence is
incorrect when registering subsystems.
Initially, the registration sequence in the gtp module was as follows:
1) rtnl_link_register();
2) genl_register_family();
3) register_pernet_subsys();
During debugging of the module, when starting the syzkaller reproducer, it
turned out that after genl_register_family() (2),
without waiting for register_pernet_subsys()(3), the /.dumpit/ event is
triggered, in which the data of the unregistered pernet subsystem is
accessed.
That is, the bug was fixed by the commit
136cfaca2256 ("gtp: fix use-after-free and null-ptr-deref in gtp_genl_dump_pdp()")[1]
and the registration sequence became as follows:
1) rtnl_link_register();
2) register_pernet_subsys();
3) genl_register_family();
However, syzkaller has discovered another problem:
after registering rtnl_link_register, the .newlink event is triggered, in
which the data of the unregistered pernet subsystem is accessed.
This problem is reproducible on current stable kernels and the latest
upstream kernel 6.8-rc6, in which the patch 136cfaca2256 [1] is applied.
Therefore, the correct sequence should be as follows:
1)register_pernet_subsys();
2) rtnl_link_register();
3) genl_register_family();
The proposed patch is developed on top of the commit changes [1], does not
conflict with it and fixes the described bug.
[1] https://lore.kernel.org/lkml/20240220160434.29bcaf43@kernel.org/T/#mb1f72c2ad57b7ea6d47333e8616beccf8bce0e23 (local)
Thanks for explaining, fix LGTM.