CVE-2026-45891: net: hns3: fix double free issue for tx spare buffer

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

net: hns3: fix double free issue for tx spare buffer

In hns3setringparam(), a temporary copy (tmprings) of the ring structure is created for rollback. However, the txspare pointer in the original ring handle is incorrectly left pointing to the old backup memory.

Later, if memory allocation fails in hns3initallring() during the setup, the error path attempts to free all newly allocated rings. Since txspare contains a stale (non-NULL) pointer from the backup, it is mistaken for a newly allocated buffer and is erroneously freed, leading to a double-free of the backup memory.

The root cause is that the txspare field was not cleared after its value was saved in tmprings, leaving a dangling pointer.

Fix this by setting txspare to NULL in the original ring structure when the creation of the new txspare fails. This ensures the error cleanup path only frees genuinely newly allocated buffers.