bpf: fix a memory leak in the LRU and LRU_PERCPU hash maps

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: bpf: fix a memory leak in the LRU and LRU_PERCPU hash maps The LRU and LRU_PERCPU maps allocate a new element on update before locking the target hash table bucket. Right after that the maps try to lock the bucket. If this fails, then maps return -EBUSY to the caller without releasing the allocated element. This makes the element untracked: it doesn't belong to either of free lists, and it doesn't belong to the hash table, so can't be re-used; this eventually leads to the permanent -ENOMEM on LRU map updates, which is unexpected. Fix this by returning the element to the local free list if bucket locking fails.

References

• https://git.kernel.org/stable/c/79ea1a12fb9a8275b6e19d4ca625dd872dedcbb9
• https://git.kernel.org/stable/c/1a9e80f757bbb1562d82e350afce2bb2f712cc3d
• https://git.kernel.org/stable/c/965e9cccbe6b9c7b379908cebcb5e3a47f20dd5e
• https://git.kernel.org/stable/c/b34ffb0c6d23583830f9327864b9c1f486003305