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Date: Mon, 1 Dec 2025 07:36:49 +0100
From: Christoph Hellwig <hch@lst.de>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: linux-block@vger.kernel.org, Keith Busch <kbusch@kernel.org>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	linux-kernel@vger.kernel.org,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	Christoph Hellwig <hch@lst.de>,
	Mike Christie <michael.christie@oracle.com>,
	linux-nvme@lists.infradead.org, Jens Axboe <axboe@kernel.dk>,
	linux-scsi@vger.kernel.org, Sagi Grimberg <sagi@grimberg.me>
Subject: Re: [PATCH v2 2/4] nvme: reject invalid pr_read_keys() num_keys
 values
Message-ID: <20251201063649.GB19461@lst.de>
References: <20251127155424.617569-1-stefanha@redhat.com> <20251127155424.617569-3-stefanha@redhat.com>
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In-Reply-To: <20251127155424.617569-3-stefanha@redhat.com>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Thu, Nov 27, 2025 at 10:54:22AM -0500, Stefan Hajnoczi wrote:
> The pr_read_keys() interface has a u32 num_keys parameter. The NVMe
> Reservation Report command has a u32 maximum length. Reject num_keys
> values that are too large to fit.
> 
> This will become important when pr_read_keys() is exposed to untrusted
> userspace via an <linux/pr.h> ioctl.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  drivers/nvme/host/pr.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/nvme/host/pr.c b/drivers/nvme/host/pr.c
> index ca6a74607b139..156a2ae1fac2e 100644
> --- a/drivers/nvme/host/pr.c
> +++ b/drivers/nvme/host/pr.c
> @@ -233,6 +233,10 @@ static int nvme_pr_read_keys(struct block_device *bdev,
>  	int ret, i;
>  	bool eds;
>  
> +	/* Check that keys fit into u32 rse_len */
> +	if (num_keys > (U32_MAX - sizeof(*rse)) / sizeof(rse->regctl_eds[0]))
> +		return -EINVAL;
> +

We use struct_size to calculate the size below, which saturates on
overflow.  So just checking the rse_len variable returned by the that
would be nicer.  Bonus points for using sizeof_field() instead of
hardcoding U32_MAX.