netdev - Re: [PATCH net-next v2] net: dccp: initialize (addr,port) listening hashtable

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Date:   Sun, 16 Dec 2018 21:51:36 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Peter Oskolkov <posk@...gle.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     Peter Oskolkov <posk.devel@...il.com>,
        Eric Dumazet <edumazet@...gle.com>,
        syzcaller <syzkaller@...glegroups.com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH net-next v2] net: dccp: initialize (addr,port) listening
 hashtable



On 12/16/2018 03:42 PM, Peter Oskolkov wrote:
> Commit d9fbc7f6431f "net: tcp: prefer listeners bound to an address"
> removes port-only listener lookups. This caused segfaults in DCCP
> lookups because DCCP did not initialize the (addr,port) hashtable.
> 
> This patch adds said initialization.
> 
> The only non-trivial issue here is the size of the new hashtable.
> It seemed reasonable to make it match the size of the port-only
> hashtable (= INET_LHTABLE_SIZE) that was used previously. Other
> parameters to inet_hashinfo2_init() match those used in TCP.
> 
> V2 changes: marked inet_hashinfo2_init as an exported symbol
> so that DCCP compiles when configured as a module.
> 
> Tested: syzcaller issues fixed; the second patch in the patchset
>         tests that DCCP lookups work correctly.
> 
> Fixes: d9fbc7f6431f "net: tcp: prefer listeners bound to an address"


Strange, I would say bug was brought by commit 61b7c691c731
("inet: Add a 2nd listener hashtable (port+addr)")

The secondary hash table would have been used anyway if some application (syzkaller-like)
had been using DCCP a bit more, to the point the second hash table would have been used.

With more than 10 listeners on one bucket, code in inet6_lookup_listener() would
have attempted to deref a NULL pointer.