CVE-2021-47317

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

powerpc/bpf: Fix detecting BPF atomic instructions

Commit 91c960b0056672 (bpf: Rename BPF_XADD and prepare to encode other atomics in .imm) converted BPF_XADD to BPF_ATOMIC and added a way to distinguish instructions based on the immediate field. Existing JIT implementations were updated to check for the immediate field and to reject programs utilizing anything more than BPF_ADD (such as BPF_FETCH) in the immediate field.

However, the check added to powerpc64 JIT did not look at the correct BPF instruction. Due to this, such programs would be accepted and incorrectly JITed resulting in soft lockups, as seen with the atomic bounds test. Fix this by looking at the correct immediate value.

Weakness

The product does not properly acquire or release a lock on a resource, leading to unexpected resource state changes and behaviors.

Affected Software

Extended Description

Locking is a type of synchronization behavior that ensures that multiple independently-operating processes or threads do not interfere with each other when accessing the same resource. All processes/threads are expected to follow the same steps for locking. If these steps are not followed precisely - or if no locking is done at all - then another process/thread could modify the shared resource in a way that is not visible or predictable to the original process. This can lead to data or memory corruption, denial of service, etc.

Potential Mitigations

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/25.html
• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/27.html

References

• https://git.kernel.org/stable/c/0d435b6d94b05dcfd836d758a63145aa566618e2
• https://git.kernel.org/stable/c/419ac821766cbdb9fd85872bb3f1a589df05c94c
• https://git.kernel.org/stable/c/7284dab07e4d51d453cc42851fae9ec4fac6ef2f
• https://git.kernel.org/stable/c/0d435b6d94b05dcfd836d758a63145aa566618e2
• https://git.kernel.org/stable/c/419ac821766cbdb9fd85872bb3f1a589df05c94c
• https://git.kernel.org/stable/c/7284dab07e4d51d453cc42851fae9ec4fac6ef2f