Re: [PATCH v2 2/6] net/handshake: Fix handshake_dup() ref counting

[Leon Romanovsky <leon@kernel.org>]

On Fri, May 05, 2023 at 08:46:01PM -0400, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> If get_unused_fd_flags() fails, we ended up calling fput(sock->file)
> twice.
> 
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  net/handshake/netlink.c |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/net/handshake/netlink.c b/net/handshake/netlink.c
> index 7ec8a76c3c8a..032d96152e2f 100644
> --- a/net/handshake/netlink.c
> +++ b/net/handshake/netlink.c
> @@ -101,10 +101,8 @@ static int handshake_dup(struct socket *sock)
>  
>  	file = get_file(sock->file);
>  	newfd = get_unused_fd_flags(O_CLOEXEC);
> -	if (newfd < 0) {
> -		fput(file);
> +	if (newfd < 0)
>  		return newfd;

IMHO, the better way to fix it is to change handshake_nl_accept_doit()
do not call to fput(sock->file) in error case. It is not right thing
to have a call to handshake_dup() and rely on elevated get_file()
for failure too as it will be problematic for future extension of
handshake_dup().

Thanks

> -	}
>  
>  	fd_install(newfd, file);
>  	return newfd;
> 
> 
>