Re: [PATCH] nfsd: hold cl_lock in client_has_state()

[Chuck Lever]

On Fri, Aug 28, 2026, at 1:29 AM, Greg KH wrote:
> On Fri, Aug 28, 2026 at 12:19:25AM -0400, Cen Zhang (Microsoft Security 
> FORGE Labs) wrote:
>> client_has_openowners() walks clp->cl_openowners and reads so_stateids
>> without clp->cl_lock. nfs4_put_stateowner() unhashes that openowner under
>> cl_lock and then frees it, so a concurrent EXCHANGE_ID with mismatched
>> creds can use-after-free the nfs4_openowner.
>> 
>> BUG: KASAN: slab-use-after-free in client_has_state+0x10a/0x140
>>   fs/nfsd/nfs4state.c:3718 client_has_openowners()
>>   nfsd4_exchange_id
>>   nfsd4_proc_compound
>>   nfsd_dispatch
>>   svc_process
>> 
>> Take clp->cl_lock while client_has_state() walks the openowner list.
>> 
>> Fixes: 4eaea1342507 ("nfsd: improve client_has_state to check for unused openowners")
>> Reported-by: Xiang Mei (Microsoft) <xmei5@xxxxxxx>
>> Cc: AutonomousCodeSecurity@xxxxxxxxxxxxx
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) <blbllhy@xxxxxxxxx>
>
> Please use your microsoft.com email address, and not a random gmail.com
> address.  It's kind of odd that Microsoft would have to rely on Google
> to send kernel patches :)

Greg, would you prefer that I hold off on applying this to nfsd-testing
until Cen can post this one again?


-- 
Chuck Lever