netdev - Re: [PATCH 5/5] drivers/s390/cio: ensure the copied buf is NULL terminated

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Date: Tue, 23 Apr 2024 08:50:52 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Bui Quang Minh <minhquangbui99@...il.com>
Cc: Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Paul M Stillwell Jr <paul.m.stillwell.jr@...el.com>,
        Rasesh Mody <rmody@...vell.com>,
        Sudarsana Kalluru <skalluru@...vell.com>, GR-Linux-NIC-Dev@...vell.com,
        Krishna Gudipati <kgudipat@...cade.com>,
        Anil Gurumurthy <anil.gurumurthy@...gic.com>,
        Sudarsana Kalluru <sudarsana.kalluru@...gic.com>,
        "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Fabian Frederick <fabf@...net.be>,
        Saurav Kashyap <skashyap@...vell.com>,
        Javed Hasan <jhasan@...vell.com>,
        GR-QLogic-Storage-Upstream@...vell.com,
        Nilesh Javali <nilesh.javali@...ium.com>,
        Arun Easi <arun.easi@...ium.com>,
        Manish Rangankar <manish.rangankar@...ium.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, intel-wired-lan@...ts.osuosl.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, Saurav Kashyap <saurav.kashyap@...ium.com>,
        linux-s390@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 5/5] drivers/s390/cio: ensure the copied buf is NULL
 terminated

On Mon, Apr 22, 2024 at 11:41:40PM +0700, Bui Quang Minh wrote:
> Currently, we allocate a lbuf-sized kernel buffer and copy lbuf from
> userspace to that buffer. Later, we use scanf on this buffer but we don't
> ensure that the string is terminated inside the buffer, this can lead to
> OOB read when using scanf. Fix this issue by allocating 1 more byte to at
> the end of buffer and write NULL terminator to the end of buffer after
> userspace copying.
> 
> Fixes: a4f17cc72671 ("s390/cio: add CRW inject functionality")
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> ---
>  drivers/s390/cio/cio_inject.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/cio/cio_inject.c b/drivers/s390/cio/cio_inject.c
> index 8613fa937237..9b69fbf49f60 100644
> --- a/drivers/s390/cio/cio_inject.c
> +++ b/drivers/s390/cio/cio_inject.c
> @@ -95,10 +95,11 @@ static ssize_t crw_inject_write(struct file *file, const char __user *buf,
>  		return -EINVAL;
>  	}
>  
> -	buffer = vmemdup_user(buf, lbuf);
> +	buffer = vmemdup_user(buf, lbuf + 1);
>  	if (IS_ERR(buffer))
>  		return -ENOMEM;
>  
> +	buffer[lbuf] = '\0';

This would read one byte too much from user space, and could potentially
fault.

Why isn't this simply memdup_user_nul() like all others, which would do the
right thing?