CVE-2022-49554

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 zspages entire page list without defending against page migration. Since pages which havent 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 theres a data race), and it can observe a spurious NULL pointer to the next page and thus not lock all of the zspages 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.

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

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