[PATCH 6.12.y 1/3] iommufd: Reject invalid read count in iommufd_fault_fops_read()

[Sasha Levin <sashal@kernel.org>]

From: Nicolin Chen <nicolinc@nvidia.com>

[ Upstream commit 47916a54eeb2a9e654512ee609f71bd5b29db702 ]

The read count must be large enough to hold one fault or a group's faults.

iommufd_fault_fops_read() does not validate the count, but returns 0 as if
the read had succeeded while leaving the pending fault in the queue.

Return -EINVAL in the undersize cases.

Fixes: 07838f7fd529 ("iommufd: Add iommufd fault object")
Link: https://patch.msgid.link/r/85c118a606fbedc5c132a1f5ec223a5ba23b92d2.1780343944.git.nicolinc@nvidia.com
Cc: stable@vger.kernel.org
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
[ sashal: applied to fault.c as 6.12 lacks the eventq.c split ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/iommu/iommufd/fault.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/iommufd/fault.c b/drivers/iommu/iommufd/fault.c
index 8226e28d79a510..6048d8a1c8380e 100644
--- a/drivers/iommu/iommufd/fault.c
+++ b/drivers/iommu/iommufd/fault.c
@@ -273,6 +273,9 @@ static ssize_t iommufd_fault_fops_read(struct file *filep, char __user *buf,
 		if (done >= count ||
 		    group->fault_count * fault_size > count - done) {
 			iommufd_fault_deliver_restore(fault, group);
+			/* Read count doesn't fit the first fault group */
+			if (done == 0)
+				rc = -EINVAL;
 			break;
 		}
 
-- 
2.53.0