linux-kernel - [PATCH] vfio: Fix ksize arg while copying user struct in vfio_df_ioctl_bind

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Message-ID: <20251030171238.1674493-1-rananta@google.com>
Date: Thu, 30 Oct 2025 17:12:38 +0000
From: Raghavendra Rao Ananta <rananta@...gle.com>
To: Jason Gunthorpe <jgg@...pe.ca>, Alex Williamson <alex.williamson@...hat.com>, 
	David Matlack <dmatlack@...gle.com>
Cc: Josh Hilke <jrhilke@...gle.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Raghavendra Rao Ananta <rananta@...gle.com>
Subject: [PATCH] vfio: Fix ksize arg while copying user struct in vfio_df_ioctl_bind_iommufd()

For the cases where user includes a non-zero value in 'token_uuid_ptr'
field of 'struct vfio_device_bind_iommufd', the copy_struct_from_user()
in vfio_df_ioctl_bind_iommufd() fails with -E2BIG. For the 'minsz' passed,
copy_struct_from_user() expects the newly introduced field to be zero-ed,
which would be incorrect in this case.

Fix this by passing the actual size of the kernel struct. If working
with a newer userspace, copy_struct_from_user() would copy the
'token_uuid_ptr' field, and if working with an old userspace, it would
zero out this field, thus still retaining backward compatibility.

Fixes: 86624ba3b522 ("vfio/pci: Do vf_token checks for VFIO_DEVICE_BIND_IOMMUFD")
Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
---
 drivers/vfio/device_cdev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vfio/device_cdev.c b/drivers/vfio/device_cdev.c
index 480cac3a0c274..8ceca24ac136c 100644
--- a/drivers/vfio/device_cdev.c
+++ b/drivers/vfio/device_cdev.c
@@ -99,7 +99,7 @@ long vfio_df_ioctl_bind_iommufd(struct vfio_device_file *df,
 		return ret;
 	if (user_size < minsz)
 		return -EINVAL;
-	ret = copy_struct_from_user(&bind, minsz, arg, user_size);
+	ret = copy_struct_from_user(&bind, sizeof(bind), arg, user_size);
 	if (ret)
 		return ret;

base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
-- 
2.51.1.930.gacf6e81ea2-goog