> On Feb 1, 2024, at 5:24 PM, NeilBrown <neilb@xxxxxxx> wrote:
>
> On Fri, 02 Feb 2024, Chuck Lever wrote:
>> Passes pynfs, fstests, and the git regression suite. Please apply
>> these to origin/linux-5.4.y.
>
> I should have mentioned this a day or two ago but I hadn't quite made
> all the connection yet...
>
> The RELEASE_LOCKOWNER bug was masking a double-free bug that was fixed
> by
> Commit 47446d74f170 ("nfsd4: add refcount for nfsd4_blocked_lock")
> which landed in v5.17 and wasn't marked as a bugfix, and so has not gone to
> stable kernels.
Then, instructions to stable@xxxxxxxxxxxxxxx:
Do not apply the patches I just sent for 5.15, 5.10, and 5.4. I will
apply 47446d74f170, run the tests again, and resend.
> Any kernel earlier than v5.17 that receives the RELEASE_LOCKOWNER fix
> also needs the nfsd4_blocked_lock fix. There is a minor follow-up fix
> for that nfsd4_blocked_lock fix which Chuck queued yesterday.
>
> The problem scenario is that an nfsd4_lock() call finds a conflicting
> lock and so has a reference to a particular nfsd4_blocked_lock. A concurrent
> nfsd4_read_lockowner call frees all the nfsd4_blocked_locks including
> the one held in nfsd4_lock(). nfsd4_lock then tries to free the
> blocked_lock it has, and results in a double-free or a use-after-free.
>
> Before either patch is applied, the extra reference on the lock-owner
> than nfsd4_lock holds causes nfsd4_realease_lockowner() to incorrectly
> return an error and NOT free the blocks_lock.
> With only the RELEASE_LOCKOWNER fix applied, the double-free happens.
Our test suite currently does not exercise this use case, apparently.
I didn't see a problem like this during testing.
> With both patches applied the refcount on the nfsd4_blocked_lock prevents
> the double-free.
>
> Kernels before 4.9 are (probably) not affected as they didn't have
> find_or_allocate_block() which takes the second reference to a shared
> object. But that is ancient history - those kernels are well past EOL.
>
> Thanks,
> NeilBrown
>
>
>>
>> ---
>>
>> Chuck Lever (2):
>> NFSD: Modernize nfsd4_release_lockowner()
>> NFSD: Add documenting comment for nfsd4_release_lockowner()
>>
>> NeilBrown (1):
>> nfsd: fix RELEASE_LOCKOWNER
>>
>>
>> fs/nfsd/nfs4state.c | 65 +++++++++++++++++++++++++--------------------
>> 1 file changed, 36 insertions(+), 29 deletions(-)
>>
>> --
>> Chuck Lever
>>
>>
>>
>
--
Chuck Lever
