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

[Jakub Sitnicki <jakub@cloudflare.com>]

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")
> Rebported-by: Xingwei Lee <xrivendell7@gmail.com>

Nit: Typo ^

> Signed-off-by: John Fastabend <john.fastabend@gmail.com>
> ---

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