linux-kernel - Re: [PATCH net] rxrpc: Fix local refcounting

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Date:   Fri, 9 Aug 2019 18:34:36 -0400
From:   Jeffrey E Altman <jaltman@...istor.com>
To:     David Howells <dhowells@...hat.com>, netdev@...r.kernel.org
Cc:     linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] rxrpc: Fix local refcounting

David,

Looks good to me.

You can add a Reviewed-by line.

Thanks.

Jeffrey Altman

On 8/9/2019 5:47 PM, David Howells wrote:
> Fix rxrpc_unuse_local() to handle a NULL local pointer as it can be called
> on an unbound socket on which rx->local is not yet set.
> 
> The following reproduced (includes omitted):
> 
> 	int main(void)
> 	{
> 		socket(AF_RXRPC, SOCK_DGRAM, AF_INET);
> 		return 0;
> 	}
> 
> causes the following oops to occur:
> 
> 	BUG: kernel NULL pointer dereference, address: 0000000000000010
> 	...
> 	RIP: 0010:rxrpc_unuse_local+0x8/0x1b
> 	...
> 	Call Trace:
> 	 rxrpc_release+0x2b5/0x338
> 	 __sock_release+0x37/0xa1
> 	 sock_close+0x14/0x17
> 	 __fput+0x115/0x1e9
> 	 task_work_run+0x72/0x98
> 	 do_exit+0x51b/0xa7a
> 	 ? __context_tracking_exit+0x4e/0x10e
> 	 do_group_exit+0xab/0xab
> 	 __x64_sys_exit_group+0x14/0x17
> 	 do_syscall_64+0x89/0x1d4
> 	 entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Reported-by: syzbot+20dee719a2e090427b5f@...kaller.appspotmail.com
> Fixes: 730c5fd42c1e ("rxrpc: Fix local endpoint refcounting")
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Jeffrey Altman <jaltman@...istor.com>
> ---
> 
>  net/rxrpc/local_object.c |   12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/net/rxrpc/local_object.c b/net/rxrpc/local_object.c
> index 9798159ee65f..c9db3e762d8d 100644
> --- a/net/rxrpc/local_object.c
> +++ b/net/rxrpc/local_object.c
> @@ -402,11 +402,13 @@ void rxrpc_unuse_local(struct rxrpc_local *local)
>  {
>  	unsigned int au;
>  
> -	au = atomic_dec_return(&local->active_users);
> -	if (au == 0)
> -		rxrpc_queue_local(local);
> -	else
> -		rxrpc_put_local(local);
> +	if (local) {
> +		au = atomic_dec_return(&local->active_users);
> +		if (au == 0)
> +			rxrpc_queue_local(local);
> +		else
> +			rxrpc_put_local(local);
> +	}
>  }
>  
>  /*
> 

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