On 1/17/20 4:28 PM, Dr. David Alan Gilbert wrote:
> * Philippe Mathieu-Daudé (philmd@redhat.com) wrote:
>> On 12/12/19 5:39 PM, Dr. David Alan Gilbert (git) wrote:
>>> From: Stefan Hajnoczi <stefanha@redhat.com>
>>>
>>> When running with multiple threads it can be tricky to handle
>>> FUSE_INIT/FUSE_DESTROY in parallel with other request types or in
>>> parallel with themselves. Serialize FUSE_INIT and FUSE_DESTROY so that
>>> malicious clients cannot trigger race conditions.
>>>
>>> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
>>> ---
>>> tools/virtiofsd/fuse_i.h | 1 +
>>> tools/virtiofsd/fuse_lowlevel.c | 18 ++++++++++++++++++
>>> 2 files changed, 19 insertions(+)
>>>
>>> diff --git a/tools/virtiofsd/fuse_i.h b/tools/virtiofsd/fuse_i.h
>>> index d0679508cd..8a4a05b319 100644
>>> --- a/tools/virtiofsd/fuse_i.h
>>> +++ b/tools/virtiofsd/fuse_i.h
>>> @@ -61,6 +61,7 @@ struct fuse_session {
>>> struct fuse_req list;
>>> struct fuse_req interrupts;
>>> pthread_mutex_t lock;
>>> + pthread_rwlock_t init_rwlock;
>>> int got_destroy;
>>> int broken_splice_nonblock;
>>> uint64_t notify_ctr;
>>> diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
>>> index 10f478b00c..9f01c05e3e 100644
>>> --- a/tools/virtiofsd/fuse_lowlevel.c
>>> +++ b/tools/virtiofsd/fuse_lowlevel.c
>>> @@ -2431,6 +2431,19 @@ void fuse_session_process_buf_int(struct fuse_session *se,
>>> req->ctx.pid = in->pid;
>>> req->ch = ch ? fuse_chan_get(ch) : NULL;
>>> + /*
>>> + * INIT and DESTROY requests are serialized, all other request types
>>> + * run in parallel. This prevents races between FUSE_INIT and ordinary
>>> + * requests, FUSE_INIT and FUSE_INIT, FUSE_INIT and FUSE_DESTROY, and
>>
>> typo "FUSE_INIT and FUSE_INIT" -> "FUSE_INIT and CUSE_INIT"?
>
> No, don't think so; I think it's suggesting a race between two
> FUSE_INIT's.
And CUSE_INIT is a subtype of FUSE_INIT, OK.
>
> Dave
>
>>> + * FUSE_DESTROY and FUSE_DESTROY.
>>> + */
>>> + if (in->opcode == FUSE_INIT || in->opcode == CUSE_INIT ||
>>> + in->opcode == FUSE_DESTROY) {
>>> + pthread_rwlock_wrlock(&se->init_rwlock);
>>> + } else {
>>> + pthread_rwlock_rdlock(&se->init_rwlock);
>>> + }
>>> +
>>> err = EIO;
>>> if (!se->got_init) {
>>> enum fuse_opcode expected;
>>> @@ -2488,10 +2501,13 @@ void fuse_session_process_buf_int(struct fuse_session *se,
>>> } else {
>>> fuse_ll_ops[in->opcode].func(req, in->nodeid, &iter);
>>> }
>>> +
>>> + pthread_rwlock_unlock(&se->init_rwlock);
>>> return;
>>> reply_err:
>>> fuse_reply_err(req, err);
>>> + pthread_rwlock_unlock(&se->init_rwlock);
>>> }
>>> #define LL_OPTION(n, o, v) \
>>> @@ -2538,6 +2554,7 @@ void fuse_session_destroy(struct fuse_session *se)
>>> se->op.destroy(se->userdata);
>>> }
>>> }
>>> + pthread_rwlock_destroy(&se->init_rwlock);
>>> pthread_mutex_destroy(&se->lock);
>>> free(se->cuse_data);
>>> if (se->fd != -1) {
>>> @@ -2631,6 +2648,7 @@ struct fuse_session *fuse_session_new(struct fuse_args *args,
>>> list_init_req(&se->list);
>>> list_init_req(&se->interrupts);
>>> fuse_mutex_init(&se->lock);
>>> + pthread_rwlock_init(&se->init_rwlock, NULL);
>>> memcpy(&se->op, op, op_size);
>>> se->owner = getuid();
>>>
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>