CVE-2021-46968

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

s390/zcrypt: fix zcard and zqueue hot-unplug memleak

Tests with kvm and a kmemdebug kernel showed, that on hot unplug the zcard and zqueue structs for the unplugged card or queue are not properly freed because of a mismatch with get/put for the embedded kref counter.

This fix now adjusts the handling of the kref counters. With init the kref counter starts with 1. This initial value needs to drop to zero with the unregister of the card or queue to trigger the release and free the object.

Weakness

The product does not sufficiently track and release allocated memory after it has been used, which slowly consumes remaining memory.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/026499a9c2e002e621ad568d1378324ae97e5524
• https://git.kernel.org/stable/c/055a063a18bcd19b93709e3eac8078d6b2f04599
• https://git.kernel.org/stable/c/70fac8088cfad9f3b379c9082832b4d7532c16c2
• https://git.kernel.org/stable/c/971dc8706cee47393d393905d294ea47e39503d3
• https://git.kernel.org/stable/c/026499a9c2e002e621ad568d1378324ae97e5524
• https://git.kernel.org/stable/c/055a063a18bcd19b93709e3eac8078d6b2f04599
• https://git.kernel.org/stable/c/70fac8088cfad9f3b379c9082832b4d7532c16c2
• https://git.kernel.org/stable/c/971dc8706cee47393d393905d294ea47e39503d3