netdev - [PATCH net-next] ipv4: Fix refcount warning for new fib

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Date:   Mon,  2 Aug 2021 10:02:21 -0600
From:   David Ahern <dsahern@...nel.org>
To:     netdev@...r.kernel.org, kuba@...nel.org, davem@...emloft.net
Cc:     ciorneiioana@...il.com, David Ahern <dsahern@...nel.org>,
        Yajun Deng <yajun.deng@...ux.dev>
Subject: [PATCH net-next] ipv4: Fix refcount warning for new fib_info

Ioana reported a refcount warning when booting over NFS:

[    5.042532] ------------[ cut here ]------------
[    5.047184] refcount_t: addition on 0; use-after-free.
[    5.052324] WARNING: CPU: 7 PID: 1 at lib/refcount.c:25 refcount_warn_saturate+0xa4/0x150
...
[    5.167201] Call trace:
[    5.169635]  refcount_warn_saturate+0xa4/0x150
[    5.174067]  fib_create_info+0xc00/0xc90
[    5.177982]  fib_table_insert+0x8c/0x620
[    5.181893]  fib_magic.isra.0+0x110/0x11c
[    5.185891]  fib_add_ifaddr+0xb8/0x190
[    5.189629]  fib_inetaddr_event+0x8c/0x140

fib_treeref needs to be set after kzalloc. The old code had a ++ which
led to the confusion when the int was replaced by a refcount_t.

Fixes: 79976892f7ea ("net: convert fib_treeref from int to refcount_t")
Signed-off-by: David Ahern <dsahern@...nel.org>
Reported-by: Ioana Ciornei <ciorneiioana@...il.com>
Cc: Yajun Deng <yajun.deng@...ux.dev>
---
 net/ipv4/fib_semantics.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index fa19f4cdf3a4..f29feb7772da 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1551,7 +1551,7 @@ struct fib_info *fib_create_info(struct fib_config *cfg,
 		return ofi;
 	}
 
-	refcount_inc(&fi->fib_treeref);
+	refcount_set(&fi->fib_treeref, 1);
 	refcount_set(&fi->fib_clntref, 1);
 	spin_lock_bh(&fib_info_lock);
 	hlist_add_head(&fi->fib_hash,
-- 
2.24.3 (Apple Git-128)