From f9d0b4220f55e321e4cfb3f8223c58a707f512ec Mon Sep 17 00:00:00 2001 From: Patrick McHardy Date: Thu, 26 Mar 2015 12:39:39 +0000 Subject: [PATCH] netfilter: nf_tables: add GC synchronization helpers GC is expected to happen asynchrously to the netlink interface. In the netlink path, both insertion and removal of elements consist of two steps, insertion followed by activation or deactivation followed by removal, during which the element must not be freed by GC. The synchronization helpers use an unused bit in the genmask field to atomically mark an element as "busy", meaning it is either currently being handled through the netlink API or by GC. Elements being processed by GC will never survive, netlink will simply ignore them. Elements being currently processed through netlink will be skipped by GC and reprocessed during the next run. Signed-off-by: Patrick McHardy Signed-off-by: Pablo Neira Ayuso --- include/net/netfilter/nf_tables.h | 35 +++++++++++++++++++++++++++++++ net/netfilter/nf_tables_api.c | 2 +- 2 files changed, 36 insertions(+), 1 deletion(-) diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h index 6fd44959bf870..1ea13fcd388ec 100644 --- a/include/net/netfilter/nf_tables.h +++ b/include/net/netfilter/nf_tables.h @@ -852,6 +852,41 @@ static inline void nft_set_elem_change_active(const struct nft_set *set, ext->genmask ^= nft_genmask_next(read_pnet(&set->pnet)); } +/* + * We use a free bit in the genmask field to indicate the element + * is busy, meaning it is currently being processed either by + * the netlink API or GC. + * + * Even though the genmask is only a single byte wide, this works + * because the extension structure if fully constant once initialized, + * so there are no non-atomic write accesses unless it is already + * marked busy. + */ +#define NFT_SET_ELEM_BUSY_MASK (1 << 2) + +#if defined(__LITTLE_ENDIAN_BITFIELD) +#define NFT_SET_ELEM_BUSY_BIT 2 +#elif defined(__BIG_ENDIAN_BITFIELD) +#define NFT_SET_ELEM_BUSY_BIT (BITS_PER_LONG - BITS_PER_BYTE + 2) +#else +#error +#endif + +static inline int nft_set_elem_mark_busy(struct nft_set_ext *ext) +{ + unsigned long *word = (unsigned long *)ext; + + BUILD_BUG_ON(offsetof(struct nft_set_ext, genmask) != 0); + return test_and_set_bit(NFT_SET_ELEM_BUSY_BIT, word); +} + +static inline void nft_set_elem_clear_busy(struct nft_set_ext *ext) +{ + unsigned long *word = (unsigned long *)ext; + + clear_bit(NFT_SET_ELEM_BUSY_BIT, word); +} + /** * struct nft_trans - nf_tables object update in transaction * diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c index 138e47fddab77..3aa92b3f85fd0 100644 --- a/net/netfilter/nf_tables_api.c +++ b/net/netfilter/nf_tables_api.c @@ -3338,7 +3338,7 @@ static int nft_add_set_elem(struct nft_ctx *ctx, struct nft_set *set, if (trans == NULL) goto err4; - ext->genmask = nft_genmask_cur(ctx->net); + ext->genmask = nft_genmask_cur(ctx->net) | NFT_SET_ELEM_BUSY_MASK; err = set->ops->insert(set, &elem); if (err < 0) goto err5; -- 2.39.5