zsmalloc: fix races between asynchronous zspage free and page migration

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: zsmalloc: fix races between asynchronous zspage free and page migration The asynchronous zspage free worker tries to lock a zspage's entire page list without defending against page migration. Since pages which haven't yet been locked can concurrently migrate off the zspage page list while lock_zspage() churns away, lock_zspage() can suffer from a few different lethal races. It can lock a page which no longer belongs to the zspage and unsafely dereference page_private(), it can unsafely dereference a torn pointer to the next page (since there's a data race), and it can observe a spurious NULL pointer to the next page and thus not lock all of the zspage's pages (since a single page migration will reconstruct the entire page list, and create_page_chain() unconditionally zeroes out each list pointer in the process). Fix the races by using migrate_read_lock() in lock_zspage() to synchronize with page migration.

References

• https://git.kernel.org/stable/c/3674d8a8dadd03a447dd21069d4dacfc3399b63b
• https://git.kernel.org/stable/c/645996efc2ae391246d595832aaa6f9d3cc338c7
• https://git.kernel.org/stable/c/fc658c083904427abbf8f18280d517ee2668677c
• https://git.kernel.org/stable/c/fae05b2314b147a78fbed1dc4c645d9a66313758
• https://git.kernel.org/stable/c/3ec459c8810e658401be428d3168eacfc380bdd0
• https://git.kernel.org/stable/c/8ba7b7c1dad1f6503c541778f31b33f7f62eb966
• https://git.kernel.org/stable/c/c5402fb5f71f1a725f1e55d9c6799c0c7bec308f
• https://git.kernel.org/stable/c/2505a981114dcb715f8977b8433f7540854851d8