Re: [PATCH bpf v1] bpf: Fix OOB in bpf_obj_memcpy for cgroup storage

[Martin KaFai Lau <martin.lau@linux.dev>]

On 3/11/26 10:25 PM, xulang wrote:
> From: Lang Xu <xulang@uniontech.com>
> 
> An out-of-bounds read occurs when copying element from a
> BPF_MAP_TYPE_CGROUP_STORAGE map to another map type with the same
> value_size that is not 8-byte aligned.
> 
> The issue happens when:
> 1. A CGROUP_STORAGE map is created with value_size not aligned to
>     8 bytes (e.g., 4 bytes)
> 2. A HASH map is created with the same value_size (e.g., 4 bytes)
> 3. Update element in 2 with data in 1

Please create a selftest for this.

pw-bot: cr

> 
> In the kernel, map elements are typically aligned to 8 bytes. However,
> bpf_cgroup_storage_calculate_size() allocates storage based on the exact
> value_size without alignment. When copy_map_value_long() is called, it
> assumes all map values are 8-byte aligned and rounds up the copy size,
> leading to a 4-byte out-of-bounds read from the cgroup storage buffer.
> 
> This patch fixes the issue by ensuring cgroup storage allocates 8-byte
> aligned buffers, matching the assumptions in copy_map_value_long().

This is fixing the src side of the "copy_map_value_long(map, dst, src)".
The src could also be from a skb? What is the value_size that the 
verifier is checking for bpf_map_update_elem?