Re: [PATCH bpf v5] bpf, cgroup: Fix storage null-ptr-deref after replacing prog

On 5/8/26 11:53, Pu Lehui wrote:
> From: Pu Lehui <[email protected]>
> 
> Syzkaller reported a storage null-ptr-deref issue after replacing prog.
> This occurs in the following scenario:
> 1. prog A, an empty prog, is attached to a cgrp.
> 2. prog B uses BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE and calls the
>    bpf_get_local_storage helper.
> 3. link_update is called to replace prog A with prog B.
> 
> The reason is that __cgroup_bpf_replace fails to alloc and assign the
> required cgrp storage for the incoming replacement prog. Consequently,
> the new prog inherits an uninit storage, leading to null-ptr-deref panic
> when kick the new prog.
> 
> Fix this by rejecting link update with -EPERM if new_prog's cgroup
> storage is incompatible with link->prog.
> 
> Fixes: 0c991ebc8c69 ("bpf: Implement bpf_prog replacement for an active bpf_cgroup_link")
> Reviewed-by: Amery Hung <[email protected]>
> Signed-off-by: Pu Lehui <[email protected]>


Looks much simpler than the previous versions.

Other than the -EPERM in the commit msg, lgtm.

Acked-by: Leon Hwang <[email protected]>

> [...]