netdev - [PATCH v1 net 16/16] ipv4: Fix a data-race around sysctl_fib_sync

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Date:   Tue, 5 Jul 2022 22:21:30 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>
CC:     Kuniyuki Iwashima <kuniyu@...zon.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        David Ahern <dsahern@...il.com>
Subject: [PATCH v1 net 16/16] ipv4: Fix a data-race around sysctl_fib_sync_mem.

While reading sysctl_fib_sync_mem, it can be changed concurrently.  So, we
need to add READ_ONCE().  Then we can set proc_douintvec_minmax_lockless()
as the handler to mark it safe.

Fixes: 9ab948a91b2c ("ipv4: Allow amount of dirty memory from fib resizing to be controllable")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
CC: David Ahern <dsahern@...il.com>
---
 net/ipv4/fib_trie.c        | 2 +-
 net/ipv4/sysctl_net_ipv4.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
index 2734c3af7e24..46e8a5125853 100644
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -498,7 +498,7 @@ static void tnode_free(struct key_vector *tn)
 		tn = container_of(head, struct tnode, rcu)->kv;
 	}
 
-	if (tnode_free_size >= sysctl_fib_sync_mem) {
+	if (tnode_free_size >= READ_ONCE(sysctl_fib_sync_mem)) {
 		tnode_free_size = 0;
 		synchronize_rcu();
 	}
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 3b1d18be0857..7ea681df37c4 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -578,7 +578,7 @@ static struct ctl_table ipv4_table[] = {
 		.data		= &sysctl_fib_sync_mem,
 		.maxlen		= sizeof(sysctl_fib_sync_mem),
 		.mode		= 0644,
-		.proc_handler	= proc_douintvec_minmax,
+		.proc_handler	= proc_douintvec_minmax_lockless,
 		.extra1		= &sysctl_fib_sync_mem_min,
 		.extra2		= &sysctl_fib_sync_mem_max,
 	},
-- 
2.30.2