CVE-2022-49697

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

bpf: Fix request_sock leak in sk lookup helpers

A customer reported a request_socket leak in a Calico cloud environment. We found that a BPF program was doing a socket lookup with takes a refcnt on the socket and that it was finding the request_socket but returning the parent LISTEN socket via sk_to_full_sk() without decrementing the child request socket 1st, resulting in request_sock slab object leak. This patch retains the existing behaviour of returning full socks to the caller but it also decrements the child request_socket if one is present before doing so to prevent the leak.

Thanks to Curtis Taylor for all the help in diagnosing and testing this. And thanks to Antoine Tenart for the reproducer and patch input.

v2 of this patch contains, refactor as per Daniel Borkmanns suggestions to validate RCU flags on the listen socket so that it balances with bpf_sk_release() and update comments as per Martin KaFai Laus suggestion. One small change to Daniels suggestion, put sk = sk2 under if (sk2 != sk) to avoid an extra instruction.

Weakness

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

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/3046a827316c0e55fc563b4fb78c93b9ca5c7c37
• https://git.kernel.org/stable/c/516760f1d2979903eaad5b437256913c5cd98416
• https://git.kernel.org/stable/c/5a62b5ba4c0ce8315b6382cd4ace81b48cd121cd
• https://git.kernel.org/stable/c/8ffe2e50e9678c8373027492035f094b130437f1
• https://git.kernel.org/stable/c/b03607437ea81b850599f705096b05b85e7a4a71