Re: [PATCH net] sch_netem: fix issues in netem_change() vs get_dist_table()

[Simon Horman <simon.horman@corigine.com>]

On Thu, Jun 22, 2023 at 06:15:03PM +0000, Eric Dumazet wrote:
> In blamed commit, I missed that get_dist_table() was allocating
> memory using GFP_KERNEL, and acquiring qdisc lock to perform
> the swap of newly allocated table with current one.
> 
> In this patch, get_dist_table() is allocating memory and
> copy user data before we acquire the qdisc lock.
> 
> Then we perform swap operations while being protected by the lock.
> 
> Note that after this patch netem_change() no longer can do partial changes.
> If an error is returned, qdisc conf is left unchanged.
> 
> Fixes: 2174a08db80d ("sch_netem: acquire qdisc lock in netem_change()")
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Stephen Hemminger <stephen@networkplumber.org>
> Cc: Jamal Hadi Salim <jhs@mojatatu.com>
> Cc: Simon Horman <simon.horman@corigine.com>
> ---
>  net/sched/sch_netem.c | 59 ++++++++++++++++++-------------------------
>  1 file changed, 25 insertions(+), 34 deletions(-)

Reviewed-by: Simon Horman <simon.horman@corigine.com>