tree 23781c50d8797a5c29e231ad82dfeb7d3e0126f7
parent a5de4ee6d055899b67bfb41722bbeb5c6e0fba70
author Cong Wang <xiyou.wangcong@gmail.com> 1600833384 -0700
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1602664386 +0200

net_sched: commit action insertions together

commit 0fedc63fadf0404a729e73a35349481c8009c02f upstream.

syzbot is able to trigger a failure case inside the loop in
tcf_action_init(), and when this happens we clean up with
tcf_action_destroy(). But, as these actions are already inserted
into the global IDR, other parallel process could free them
before tcf_action_destroy(), then we will trigger a use-after-free.

Fix this by deferring the insertions even later, after the loop,
and committing all the insertions in a separate loop, so we will
never fail in the middle of the insertions any more.

One side effect is that the window between alloction and final
insertion becomes larger, now it is more likely that the loop in
tcf_del_walker() sees the placeholder -EBUSY pointer. So we have
to check for error pointer in tcf_del_walker().

Reported-and-tested-by: syzbot+2287853d392e4b42374a@syzkaller.appspotmail.com
Fixes: 0190c1d452a9 ("net: sched: atomically check-allocate action")
Cc: Vlad Buslov <vladbu@mellanox.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>