[PATCH 5.15 035/135] netfilter: use get_random_u32 instead of prandom

Greg Kroah-Hartman
2022-06-27T11:41:19Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit b1fd94e704571f98b21027340eecf821b2bdffba ]

bh might occur while updating per-cpu rnd_state from user context,
ie. local_out path.

BUG: using smp_processor_id() in preemptible [00000000] code: nginx/2725
caller is nft_ng_random_eval+0x24/0x54 [nft_numgen]
Call Trace:
check_preemption_disabled+0xde/0xe0
nft_ng_random_eval+0x24/0x54 [nft_numgen]

Use the random driver instead, this also avoids need for local prandom
state. Moreover, prandom now uses the random driver since d4150779e60f
("random32: use real rng for non-deterministic randomness").

Based on earlier patch from Pablo Neira.

Fixes: 6b2faee0ca91 ("netfilter: nft_meta: place prandom handling in a helper")
Fixes: 978d8f9055c3 ("netfilter: nft_numgen: add map lookups for numgen random operations")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nft_meta.c | 13 ++-----------
net/netfilter/nft_numgen.c | 12 +++---------
2 files changed, 5 insertions(+), 20 deletions(-)

diff --git a/net/netfilter/nft_meta.c b/net/netfilter/nft_meta.c
index a7e01e9952f1..44d9b38e5f90 100644
--- a/net/netfilter/nft_meta.c
+++ b/net/netfilter/nft_meta.c
@@ -14,6 +14,7 @@
#include <linux/in.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
+#include <linux/random.h>
#include <linux/smp.h>
#include <linux/static_key.h>
#include <net/dst.h>
@@ -32,8 +33,6 @@
#define NFT_META_SECS_PER_DAY 86400
#define NFT_META_DAYS_PER_WEEK 7

-static DEFINE_PER_CPU(struct rnd_state, nft_prandom_state);
-
static u8 nft_meta_weekday(void)
{
time64_t secs = ktime_get_real_seconds();
@@ -267,13 +266,6 @@ static bool nft_meta_get_eval_ifname(enum nft_meta_keys key, u32 *dest,
return true;
}

-static noinline u32 nft_prandom_u32(void)
-{
- struct rnd_state *state = this_cpu_ptr(&nft_prandom_state);
-
- return prandom_u32_state(state);
-}
-
#ifdef CONFIG_IP_ROUTE_CLASSID
static noinline bool
nft_meta_get_eval_rtclassid(const struct sk_buff *skb, u32 *dest)
@@ -385,7 +377,7 @@ void nft_meta_get_eval(const struct nft_expr *expr,
break;
#endif
case NFT_META_PRANDOM:
- *dest = nft_prandom_u32();
+ *dest = get_random_u32();
break;
#ifdef CONFIG_XFRM
case NFT_META_SECPATH:
@@ -514,7 +506,6 @@ int nft_meta_get_init(const struct nft_ctx *ctx,
len = IFNAMSIZ;
break;
case NFT_META_PRANDOM:
- prandom_init_once(&nft_prandom_state);
len = sizeof(u32);
break;
#ifdef CONFIG_XFRM
diff --git a/net/netfilter/nft_numgen.c b/net/netfilter/nft_numgen.c
index 722cac1e90e0..4e43214e88de 100644
--- a/net/netfilter/nft_numgen.c
+++ b/net/netfilter/nft_numgen.c
@@ -9,12 +9,11 @@
#include <linux/netlink.h>
#include <linux/netfilter.h>
#include <linux/netfilter/nf_tables.h>
+#include <linux/random.h>
#include <linux/static_key.h>
#include <net/netfilter/nf_tables.h>
#include <net/netfilter/nf_tables_core.h>

-static DEFINE_PER_CPU(struct rnd_state, nft_numgen_prandom_state);
-
struct nft_ng_inc {
u8 dreg;
u32 modulus;
@@ -104,12 +103,9 @@ struct nft_ng_random {
u32 offset;
};

-static u32 nft_ng_random_gen(struct nft_ng_random *priv)
+static u32 nft_ng_random_gen(const struct nft_ng_random *priv)
{
- struct rnd_state *state = this_cpu_ptr(&nft_numgen_prandom_state);
-
- return reciprocal_scale(prandom_u32_state(state), priv->modulus) +
- priv->offset;
+ return reciprocal_scale(get_random_u32(), priv->modulus) + priv->offset;
}

static void nft_ng_random_eval(const struct nft_expr *expr,
@@ -137,8 +133,6 @@ static int nft_ng_random_init(const struct nft_ctx *ctx,
if (priv->offset + priv->modulus - 1 < priv->offset)
return -EOVERFLOW;

- prandom_init_once(&nft_numgen_prandom_state);
-
return nft_parse_register_store(ctx, tb[NFTA_NG_DREG], &priv->dreg,
NULL, NFT_DATA_VALUE, sizeof(u32));
}
--
2.35.1