Re: [PATCH v2 2/4] nvme: reject invalid pr_read_keys() num_keys values

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Dec 01, 2025 at 07:36:49AM +0100, Christoph Hellwig wrote:
> 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.

Will fix. I don't see how to use sizeof_field() here, but taking
advantage of struct_size() already improves things a lot:

diff --git a/drivers/nvme/host/pr.c b/drivers/nvme/host/pr.c
index ca6a74607b139..ad2ecc2f49a97 100644
--- a/drivers/nvme/host/pr.c
+++ b/drivers/nvme/host/pr.c
@@ -228,7 +228,8 @@ static int nvme_pr_resv_report(struct block_device *bdev, void *data,
 static int nvme_pr_read_keys(struct block_device *bdev,
                struct pr_keys *keys_info)
 {
-       u32 rse_len, num_keys = keys_info->num_keys;
+       size_t rse_len;
+       u32 num_keys = keys_info->num_keys;
        struct nvme_reservation_status_ext *rse;
        int ret, i;
        bool eds;
@@ -238,6 +239,9 @@ static int nvme_pr_read_keys(struct block_device *bdev,
         * enough to get enough keys to fill the return keys buffer.
         */
        rse_len = struct_size(rse, regctl_eds, num_keys);
+       if (rse_len > U32_MAX)
+               return -EINVAL;
+
        rse = kzalloc(rse_len, GFP_KERNEL);
        if (!rse)
                return -ENOMEM;

Stefan

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