Re: [PATCH 101/104] virtiofsd: prevent FUSE_INIT/FUSE_DESTROY races

[Dr. David Alan Gilbert]

* Masayoshi Mizuma (address@hidden) wrote:
> On Thu, Dec 12, 2019 at 04:39:01PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: Stefan Hajnoczi <address@hidden>
> > 
> > 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 <address@hidden>
> > ---
> >  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
> > +     * 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();
> 
> Looks good to me.
> 
> Reviewed-by: Masayoshi Mizuma <address@hidden>

Thanks

> > -- 
> > 2.23.0
> > 
> > 
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK