CVE-2021-47061

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

KVM: Destroy I/O bus devices on unregister failure after syncing SRCU

If allocating a new instance of an I/O bus fails when unregistering a device, wait to destroy the device until after all readers are guaranteed to see the new null bus. Destroying devices before the bus is nullified could lead to use-after-free since readers expect the devices on their reference of the bus to remain valid.

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/03c6cccedd3913006744faa252a4da5145299343
• https://git.kernel.org/stable/c/2ee3757424be7c1cd1d0bbfa6db29a7edd82a250
• https://git.kernel.org/stable/c/30f46c6993731efb2a690c9197c0fd9ed425da2d
• https://git.kernel.org/stable/c/4e899ca848636b37e9ac124bc1723862a7d7d927
• https://git.kernel.org/stable/c/03c6cccedd3913006744faa252a4da5145299343
• https://git.kernel.org/stable/c/2ee3757424be7c1cd1d0bbfa6db29a7edd82a250
• https://git.kernel.org/stable/c/30f46c6993731efb2a690c9197c0fd9ed425da2d
• https://git.kernel.org/stable/c/4e899ca848636b37e9ac124bc1723862a7d7d927