From e7820e39b7d19b9fe1928fc19de9361b44150ca6 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 21 Nov 2014 11:47:16 -0800 Subject: [PATCH] net: Revert "net: avoid one atomic operation in skb_clone()" Not sure what I was thinking, but doing anything after releasing a refcount is suicidal or/and embarrassing. By the time we set skb->fclone to SKB_FCLONE_FREE, another cpu could have released last reference and freed whole skb. We potentially corrupt memory or trap if CONFIG_DEBUG_PAGEALLOC is set. Reported-by: Chris Mason Fixes: ce1a4ea3f1258 ("net: avoid one atomic operation in skb_clone()") Signed-off-by: Eric Dumazet Cc: Sabrina Dubroca Signed-off-by: David S. Miller --- net/core/skbuff.c | 23 ++++++----------------- 1 file changed, 6 insertions(+), 17 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index c16615bfb61e..32e31c299631 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -552,20 +552,13 @@ static void kfree_skbmem(struct sk_buff *skb) case SKB_FCLONE_CLONE: fclones = container_of(skb, struct sk_buff_fclones, skb2); - /* Warning : We must perform the atomic_dec_and_test() before - * setting skb->fclone back to SKB_FCLONE_FREE, otherwise - * skb_clone() could set clone_ref to 2 before our decrement. - * Anyway, if we are going to free the structure, no need to - * rewrite skb->fclone. + /* The clone portion is available for + * fast-cloning again. */ - if (atomic_dec_and_test(&fclones->fclone_ref)) { + skb->fclone = SKB_FCLONE_FREE; + + if (atomic_dec_and_test(&fclones->fclone_ref)) kmem_cache_free(skbuff_fclone_cache, fclones); - } else { - /* The clone portion is available for - * fast-cloning again. - */ - skb->fclone = SKB_FCLONE_FREE; - } break; } } @@ -887,11 +880,7 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask) if (skb->fclone == SKB_FCLONE_ORIG && n->fclone == SKB_FCLONE_FREE) { n->fclone = SKB_FCLONE_CLONE; - /* As our fastclone was free, clone_ref must be 1 at this point. - * We could use atomic_inc() here, but it is faster - * to set the final value. - */ - atomic_set(&fclones->fclone_ref, 2); + atomic_inc(&fclones->fclone_ref); } else { if (skb_pfmemalloc(skb)) gfp_mask |= __GFP_MEMALLOC; -- 2.20.1