mm/gup: fix memfd_pin_folios alloc race panic

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: mm/gup: fix memfd_pin_folios alloc race panic If memfd_pin_folios tries to create a hugetlb page, but someone else already did, then folio gets the value -EEXIST here: folio = memfd_alloc_folio(memfd, start_idx); if (IS_ERR(folio)) { ret = PTR_ERR(folio); if (ret != -EEXIST) goto err; then on the next trip through the "while start_idx" loop we panic here: if (folio) { folio_put(folio); To fix, set the folio to NULL on error.

References

• https://git.kernel.org/stable/c/e28f39b359c0cfdcc011603e51187085a5f1e5e3
• https://git.kernel.org/stable/c/ce645b9fdc78ec5d28067286e92871ddae6817d5