On Wed, 2016-01-06 at 00:18 -0800, Francesco Ruggeri wrote:
> dst_release should not access dst->flags after decrementing
> __refcnt to 0. The dst_entry may be in dst_busy_list and
> dst_gc_task may dst_destroy it before dst_release gets a chance
> to access dst->flags.
>
> Signed-off-by: Francesco Ruggeri <[email protected]>
> ---
> net/core/dst.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/dst.c b/net/core/dst.c
> index e6dc772..a1656e3 100644
> --- a/net/core/dst.c
> +++ b/net/core/dst.c
> @@ -301,12 +301,13 @@ void dst_release(struct dst_entry *dst)
> {
> if (dst) {
> int newrefcnt;
> + unsigned short nocache = dst->flags & DST_NOCACHE;
>
> newrefcnt = atomic_dec_return(&dst->__refcnt);
> if (unlikely(newrefcnt < 0))
> net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
> __func__, dst, newrefcnt);
> - if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE))
> + if (!newrefcnt && unlikely(nocache))
> call_rcu(&dst->rcu_head, dst_destroy_rcu);
> }
> }
You're right.
My previous fix (commit d69bbf88c8d0) was okay only for DST_NOCACHE dst.
Fixes: d69bbf88c8d0 ("net: fix a race in dst_release()")
Fixes: 27b75c95f10d ("net: avoid RCU for NOCACHE dst")
Acked-by: Eric Dumazet <[email protected]>
Thanks !
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