Re: [PATCH v4] IB/sa: Resolving use-after-free in ib_nl_send_msg
From: Jason Gunthorpe
Date: Wed Aug 25 2021 - 13:26:35 EST
On Mon, Aug 23, 2021 at 04:54:16PM +0000, Haakon Bugge wrote:
> > On 8 Jul 2020, at 03:12, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
> > On Tue, Jul 07, 2020 at 06:05:02PM -0700, Divya Indi wrote:
> >> Thanks Jason.
> >> Appreciate your help and feedback for fixing this issue.
> >> Would it be possible to access the edited version of the patch?
> >> If yes, please share a pointer to the same.
> > https://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git/commit/?h=for-rc&id=f427f4d6214c183c474eeb46212d38e6c7223d6a
> Hi Jason,
> At first glanse, this commit calls rdma_nl_multicast() whilst
> holding a spinlock. Since rdma_nl_multicast() is called with a
> gfp_flag parameter, one could assume it supports an atomic
> context. rdma_nl_multicast() ends up in
> netlink_broadcast_filtered(). This function calls
> netlink_lock_table(), which calls read_unlock_irqrestore(), which
> ends up calling _raw_read_unlock_irqrestore(). And here
> preempt_enable() is called :-(
I don't understand. This:
unsigned long flags;
Is perfectly fine in an atomic context.
preempt_enable is implemented as a nesting counter, so it is fine to
call it from inside an atomic region so long as it is balanced.