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

On 2026/8/5 12:59, Leon Hwang wrote:
> 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.

Thanks review, I'd better send a new version first.

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