diff options
| author | Eric Dumazet <edumazet@google.com> | 2014-11-21 11:47:16 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-11-21 15:26:32 -0500 |
| commit | e7820e39b7d19b9fe1928fc19de9361b44150ca6 (patch) | |
| tree | 15599feec720efe469184ed07d9eefc91c32a086 /net | |
| parent | 892d6eb1245b771987afb8667a65344e568d3439 (diff) | |
| download | lwn-e7820e39b7d19b9fe1928fc19de9361b44150ca6.tar.gz lwn-e7820e39b7d19b9fe1928fc19de9361b44150ca6.zip | |
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 <clm@fb.com>
Fixes: ce1a4ea3f1258 ("net: avoid one atomic operation in skb_clone()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
| -rw-r--r-- | net/core/skbuff.c | 23 |
1 files 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; |