In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix OOB in pcpu_init_value
An out-of-bounds read occurs when copying element from a BPF_MAP_TYPE_CGROUP_STORAGE map to another pcpu map with the same value_size that is not rounded up to 8 bytes.
The issue happens when:
- A CGROUP_STORAGE map is created with value_size not aligned to
- A pcpu map is created with the same value_size (e.g., 4 bytes)
- Update element in 2 with data in 1
pcpu_init_value assumes that all sources are rounded up to 8 bytes, and invokes copy_map_value_long to make a data copy, However, the assumption doesn't stand since there are some cases where the source may not be rounded up to 8 bytes, e.g., CGROUP_STORAGE, skb->data. the verifier verifies exactly the size that the source claims, not the size rounded up to 8 bytes by kernel, an OOB happens when the source has only 4 bytes while the copy size(4) is rounded up to 8.