CVE-2024-50020: ice: Fix improper handling of refcount in ice_sriov_set_msix_vec_count()

In the Linux kernel, the following vulnerability has been resolved:

ice: Fix improper handling of refcount in icesriovsetmsixveccount()

This patch addresses an issue with improper reference count handling in the icesriovsetmsixveccount() function.

First, the function calls icegetvfbyid(), which increments the reference count of the vf pointer. If the subsequent call to icegetvfvsi() fails, the function currently returns an error without decrementing the reference count of the vf pointer, leading to a reference count leak. The correct behavior, as implemented in this patch, is to decrement the reference count using iceputvf(vf) before returning an error when vsi is NULL.

Second, the function calls icesriovgetirqs(), which sets vf->firstvectoridx. If this call returns a negative value, indicating an error, the function returns an error without decrementing the reference count of the vf pointer, resulting in another reference count leak. The patch addresses this by adding a call to iceputvf(vf) before returning an error when vf->firstvectoridx < 0.

This bug was identified by an experimental static analysis tool developed by our team. The tool specializes in analyzing reference count operations and identifying potential mismanagement of reference counts. In this case, the tool flagged the missing decrement operation as a potential issue, leading to this patch.