netfilter: nft_inner: Use nested-BH locking for nft_pcpu_tun_ctx

nft_pcpu_tun_ctx is a per-CPU variable and relies on disabled BH for its
locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT
this data structure requires explicit locking.

Make a struct with a nft_inner_tun_ctx member (original
nft_pcpu_tun_ctx) and a local_lock_t and use local_lock_nested_bh() for
locking. This change adds only lockdep coverage and does not alter the
functional behaviour for !PREEMPT_RT.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nft_inner.c b/net/netfilter/nft_inner.c
index 817ab978d24a19c32904a1861c390dc1dd99938d..c4569d4b92285338b903b7d876efcba09238f0ca 100644 (file)
--- a/net/netfilter/nft_inner.c
+++ b/net/netfilter/nft_inner.c
@@ -23,7 +23,14 @@
 #include <linux/ip.h>
 #include <linux/ipv6.h>
 
-static DEFINE_PER_CPU(struct nft_inner_tun_ctx, nft_pcpu_tun_ctx);
+struct nft_inner_tun_ctx_locked {
+       struct nft_inner_tun_ctx ctx;
+       local_lock_t bh_lock;
+};
+
+static DEFINE_PER_CPU(struct nft_inner_tun_ctx_locked, nft_pcpu_tun_ctx) = {
+       .bh_lock = INIT_LOCAL_LOCK(bh_lock),
+};
 
 /* Same layout as nft_expr but it embeds the private expression data area. */
 struct __nft_expr {
@@ -237,12 +244,15 @@ static bool nft_inner_restore_tun_ctx(const struct nft_pktinfo *pkt,
        struct nft_inner_tun_ctx *this_cpu_tun_ctx;
 
        local_bh_disable();
-       this_cpu_tun_ctx = this_cpu_ptr(&nft_pcpu_tun_ctx);
+       local_lock_nested_bh(&nft_pcpu_tun_ctx.bh_lock);
+       this_cpu_tun_ctx = this_cpu_ptr(&nft_pcpu_tun_ctx.ctx);
        if (this_cpu_tun_ctx->cookie != (unsigned long)pkt->skb) {
                local_bh_enable();
+               local_unlock_nested_bh(&nft_pcpu_tun_ctx.bh_lock);
                return false;
        }
        *tun_ctx = *this_cpu_tun_ctx;
+       local_unlock_nested_bh(&nft_pcpu_tun_ctx.bh_lock);
        local_bh_enable();
 
        return true;
@@ -254,9 +264,11 @@ static void nft_inner_save_tun_ctx(const struct nft_pktinfo *pkt,
        struct nft_inner_tun_ctx *this_cpu_tun_ctx;
 
        local_bh_disable();
-       this_cpu_tun_ctx = this_cpu_ptr(&nft_pcpu_tun_ctx);
+       local_lock_nested_bh(&nft_pcpu_tun_ctx.bh_lock);
+       this_cpu_tun_ctx = this_cpu_ptr(&nft_pcpu_tun_ctx.ctx);
        if (this_cpu_tun_ctx->cookie != tun_ctx->cookie)
                *this_cpu_tun_ctx = *tun_ctx;
+       local_unlock_nested_bh(&nft_pcpu_tun_ctx.bh_lock);
        local_bh_enable();
 }