netdev - Re: [PATCH bpf 1/5] bpf: sockmap, fix proto update hook to avoid dup calls

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Message-ID: <841935e8-f075-4fc4-9f1b-3451ad6e1f98@linux.dev>
Date: Wed, 3 Jan 2024 17:00:21 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jakub Sitnicki <jakub@...udflare.com>,
 John Fastabend <john.fastabend@...il.com>
Cc: rivendell7@...il.com, kuniyu@...zon.com, bpf@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH bpf 1/5] bpf: sockmap, fix proto update hook to avoid dup
 calls

On 1/2/24 4:00 AM, Jakub Sitnicki wrote:
> On Thu, Dec 21, 2023 at 03:23 PM -08, John Fastabend wrote:
>> When sockets are added to a sockmap or sockhash we allocate and init a
>> psock. Then update the proto ops with sock_map_init_proto the flow is
>>
>>    sock_hash_update_common
>>      sock_map_link
>>        psock = sock_map_psock_get_checked() <-returns existing psock
>>        sock_map_init_proto(sk, psock)       <- updates sk_proto
>>
>> If the socket is already in a map this results in the sock_map_init_proto
>> being called multiple times on the same socket. We do this because when
>> a socket is added to multiple maps this might result in a new set of BPF
>> programs being attached to the socket requiring an updated ops struct.
>>
>> This creates a rule where it must be safe to call psock_update_sk_prot
>> multiple times. When we added a fix for UAF through unix sockets in patch
>> 4dd9a38a753fc we broke this rule by adding a sock_hold in that path
>> to ensure the sock is not released. The result is if a af_unix stream sock
>> is placed in multiple maps it results in a memory leak because we call
>> sock_hold multiple times with only a single sock_put on it.
>>
>> Fixes: 4dd9a38a753fc ("bpf: sockmap, fix proto update hook to avoid dup calls")

The Fixes tag looks wrong ;)

I changed it to

Fixes: 8866730aed51 ("bpf, sockmap: af_unix stream sockets need to hold ref for 
pair sock")

>> Rebported-by: Xingwei Lee <xrivendell7@...il.com>
> 
> Nit: Typo ^

yep. fixed.

Also added the missing "test_sockmap_pass_prog__destroy(skel)" to the 
sockmap_basic.c selftest.

Applied. Thanks for the fixes and the review.