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Subject: Re: [PATCH] aio: prevent the final fput() in the middle of vfs_poll()
 (Re: KASAN: use-after-free Read in unix_dgram_poll)
To:     Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     davem@davemloft.net, jbaron@akamai.com, kgraul@linux.ibm.com,
        ktkhai@virtuozzo.com, kyeongdon.kim@lge.com,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        pabeni@redhat.com, syzkaller-bugs@googlegroups.com,
        xiyou.wangcong@gmail.com, hch@lst.de
References: <000000000000f39c7b05832e0219@google.com>
 <20190303135502.GP2217@ZenIV.linux.org.uk>
 <20190303151846.GQ2217@ZenIV.linux.org.uk>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <dd9d445c-4adc-67a7-8957-01f38cb39a70@gmail.com>
Date:   Sun, 3 Mar 2019 10:37:37 -0800
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On 03/03/2019 07:18 AM, Al Viro wrote:

> Fixes: bfe4037e722ec
> Cc: stable@vger.kernel.org
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> diff --git a/fs/aio.c b/fs/aio.c
> index 3083180a54c8..7e88bfabdac2 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1767,6 +1767,7 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
>  
>  	/* one for removal from waitqueue, one for this function */
>  	refcount_set(&aiocb->ki_refcnt, 2);
> +	get_file(req->file);
>  
>  	mask = vfs_poll(req->file, &apt.pt) & req->events;
>  	if (unlikely(!req->head)) {
> @@ -1793,6 +1794,7 @@ static ssize_t aio_poll(struct aio_kiocb *aiocb, const struct iocb *iocb)
>  	spin_unlock_irq(&ctx->ctx_lock);
>  
>  out:
> +	fput(req->file);
>  	if (unlikely(apt.error)) {
>  		fput(req->file);
>  		return apt.error;
> 

Very nice changelog Al, thanks for fixing this.

Reviewed-by: Eric Dumazet <edumazet@google.com>