[PATCH for-next V2] RDMA/core: Fix storing node description

[PATCH for-next V2] RDMA/core: Fix storing node description

[Kamal Heib]

Make sure to return -EINVAL when the supplied string is bigger then
the node_desc array.

Fixes: c5bcbbb9fe00 ("IB: Allow userspace to set node description")
Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
---
 drivers/infiniband/core/sysfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/sysfs.c b/drivers/infiniband/core/sysfs.c
index 087682e6969e..aa90a42d6565 100644
--- a/drivers/infiniband/core/sysfs.c
+++ b/drivers/infiniband/core/sysfs.c
@@ -1268,7 +1268,9 @@ static ssize_t node_desc_store(struct device *device,
 	if (!dev->ops.modify_device)
 		return -EOPNOTSUPP;
 
-	memcpy(desc.node_desc, buf, min_t(int, count, IB_DEVICE_NODE_DESC_MAX));
+	if (strscpy(desc.node_desc, buf, sizeof(desc.node_desc)) == -E2BIG)
+		return -EINVAL;
+
 	ret = ib_modify_device(dev, IB_DEVICE_MODIFY_NODE_DESC, &desc);
 	if (ret)
 		return ret;
-- 
2.21.1

Re: [PATCH for-next V2] RDMA/core: Fix storing node description

[Jason Gunthorpe]

On Tue, Jan 14, 2020 at 10:14:55AM +0200, Kamal Heib wrote:
> Make sure to return -EINVAL when the supplied string is bigger then
> the node_desc array.
> 
> Fixes: c5bcbbb9fe00 ("IB: Allow userspace to set node description")
> Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
> ---
>  drivers/infiniband/core/sysfs.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/core/sysfs.c b/drivers/infiniband/core/sysfs.c
> index 087682e6969e..aa90a42d6565 100644
> --- a/drivers/infiniband/core/sysfs.c
> +++ b/drivers/infiniband/core/sysfs.c
> @@ -1268,7 +1268,9 @@ static ssize_t node_desc_store(struct device *device,
>  	if (!dev->ops.modify_device)
>  		return -EOPNOTSUPP;
>  
> -	memcpy(desc.node_desc, buf, min_t(int, count, IB_DEVICE_NODE_DESC_MAX));
> +	if (strscpy(desc.node_desc, buf, sizeof(desc.node_desc)) == -E2BIG)
> +		return -EINVAL;
> +

So, while this is the preferred code, when I checked on how this all
works what I found was madness.

The desc.node_desc is not a string. It is an array of 64 bytes, where
all 64 bits can be valid without a null termination.

Code that accesses the array like:

drivers/infiniband/core/sysfs.c:        return sprintf(buf, "%.64s\n", dev->node_desc);

Is 'correct', while code like this:

drivers/infiniband/hw/bnxt_re/main.c:   return scnprintf(buf, PAGE_SIZE, "%s\n", rdev->ibdev.node_desc);

Is wrong, it could run past the end of the character array.

Obviously this is all insane. If I apply your patch then userspace
looses the ability to have a 64 character node description.

If you want to persue this then please fix the underlying issue - make
node_desc into an always null terminated string:
 - Increase the width to 65
 - Never use memcpy to manipulate it
 - Devices should set it from the mad/device array using
    scnprintf(dev->node_desc, sizeof(dev->node_desc), "%.64s\n", mad_desc)
   Perhaps this should be a helper function
 - Devices should read it into a MAD format using some approach
   zero fills
 - Get rid of all the .64 format strings

Thanks,
Jason