Re: [PATCH] flow: fix podman issue #25959

[Stefano Brivio <sbrivio@redhat.com>]

On Wed, 30 Apr 2025 18:05:25 +0200
Laurent Vivier <lvivier@redhat.com> wrote:

> While running piHole using podman, traffic can trigger the following
> assert:
> 
> ASSSERTION FAILED in flow_alloc (flow.c:521): flow->f.state == FLOW_STATE_FREE
> 
> Backtrace shows that this happens in flow_defer_handler():
> 
>     #4  0x00005610d6f5b481 flow_alloc (passt + 0xb481)
>     #5  0x00005610d6f74f86 udp_flow_from_sock (passt + 0x24f86)
>     #6  0x00005610d6f737c3 udp_sock_fwd (passt + 0x237c3)
>     #7  0x00005610d6f74c07 udp_flush_flow (passt + 0x24c07)
>     #8  0x00005610d6f752c2 udp_flow_defer (passt + 0x252c2)
>     #9  0x00005610d6f5bce1 flow_defer_handler (passt + 0xbce1)
> 
> We are trying to allocate a new flow inside the loop freeing them.
> 
> Inside the loop free_head points to the first free flow entry in the
> current cluster. But if we allocate a new entry during the loop,
> free_head is not updated and can point now to the entry we have just
> allocated.
> 
> We can fix the problem by spliting the loop in two parts:
> - first part where we can close some of them and allocate some new
>   flow entries,
> - second part where we free the entries closed in the previous loop
>   and we aggregate the free entries to merge consecutive the clusters.
> 
> Link: https://github.com/containers/podman/issues/25959
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>

Applied, thanks!

-- 
Stefano