netdev - [PATCH net-next] rhashtable: Make sure max

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Message-Id: <20170427223024.32657-1-f.fainelli@gmail.com>
Date:   Thu, 27 Apr 2017 15:30:24 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, herbert@...dor.apana.org.au, fw@...len.de,
        tgraf@...g.ch, Florian Fainelli <f.fainelli@...il.com>
Subject: [PATCH net-next] rhashtable: Make sure max_size is non zero

After commit 6d684e54690c ("rhashtable: Cap total number of
entries to 2^31"), we would be hitting a panic() in net/core/rtnetlink.c
during initialization. The call stack would look like this:

register_pernet_subsys()
    ...
    ops->init()
	rtnetlink_net_init()
	  netlink_kernel_create()
	     netlink_insert()
		__netlink_insert()
		   rhashtable_lookup_insert_key()
		      __rhashtable_insert_fast()
			rht_grow_above_max()

And here, we have rht_grow_above_max() return true, because ht->nelemts = 0 (legit)
&& ht->max_elems = 0 (looks bogus).

Eventually, we would be return -E2BIG from __rhashtable_insert_fast()
and propagate this all the way back to the caller.

After commit 6d684e54690c what changed is that we would take the
following condition:

if (ht->p.max_size < ht->max_elems / 2)
	ht->max_elems = ht->p.max_size * 2;

and since ht->p.max_size = 0, we would set ht->max_elems to 0 as well.

Fix this by taking this branch only when ht->p.max_size is non-zero

Fixes: Fixes: 6d684e54690c ("rhashtable: Cap total number of entries to 2^31")
Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
---
 lib/rhashtable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 751630bbe409..6b4f07760fec 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -963,7 +963,7 @@ int rhashtable_init(struct rhashtable *ht,
 
 	/* Cap total entries at 2^31 to avoid nelems overflow. */
 	ht->max_elems = 1u << 31;
-	if (ht->p.max_size < ht->max_elems / 2)
+	if (ht->p.max_size && (ht->p.max_size < ht->max_elems / 2))
 		ht->max_elems = ht->p.max_size * 2;
 
 	ht->p.min_size = max(ht->p.min_size, HASH_MIN_SIZE);
-- 
2.12.2