Re: [PATCH 4.14] net/sched: cls_u32: Fix reference counter leak leading to overflow

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Jul 27, 2023 at 07:15:54PM +0000, Rishabh Bhatnagar wrote:
> From: Lee Jones <lee@kernel.org>
> 
> Upstream commit 04c55383fa5689357bcdd2c8036725a55ed632bc.
> 
> In the event of a failure in tcf_change_indev(), u32_set_parms() will
> immediately return without decrementing the recently incremented
> reference counter.  If this happens enough times, the counter will
> rollover and the reference freed, leading to a double free which can be
> used to do 'bad things'.
> 
> In order to prevent this, move the point of possible failure above the
> point where the reference counter is incremented.  Also save any
> meaningful return values to be applied to the return data at the
> appropriate point in time.
> 
> This issue was caught with KASAN.
> 
> Fixes: 705c7091262d ("net: sched: cls_u32: no need to call tcf_exts_change for newly allocated struct")
> Suggested-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Lee Jones <lee@kernel.org>
> Reviewed-by: Eric Dumazet <edumazet@google.com>
> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Rishabh Bhatnagar <risbhat@amazon.com>
> ---
>  net/sched/cls_u32.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)

We need a 4.19.y backport before we can apply a 4.14.y version, as you
do not want to upgrade and have a regression.

thanks,

greg k-h