Re: [PATCH for-next 02/10] RDMA/rtrs-srv: Prevent sysfs error with path name "ctl"

[Haris Iqbal <haris.iqbal@ionos.com>]

On Mon, Aug 2, 2021 at 8:47 AM Leon Romanovsky <leon@kernel.org> wrote:
>
> On Fri, Jul 30, 2021 at 03:18:24PM +0200, Jack Wang wrote:
> > From: Gioh Kim <gi-oh.kim@ionos.com>
> >
> > If the client tries to create a path with name "ctl",
> > the server tries to creates /sys/devices/virtual/rtrs-server/ctl/.
> > Then server generated below error because there is already ctl directory
> > which manages some setup of the server.
> >
> > sysfs: cannot create duplicate filename '/devices/virtual/rtrs-server/ctl'
> > Workqueue: ib-comp-wq ib_cq_poll_work [ib_core]
> > Call Trace:
> > dump_stack+0x50/0x63
> > sysfs_warn_dup.cold+0x17/0x24
> > sysfs_create_dir_ns+0xb6/0xd0
> > kobject_add_internal+0xa6/0x2a0
> > kobject_add+0x7e/0xb0
> > ? _cond_resched+0x15/0x30
> > device_add+0x121/0x640
> > rtrs_srv_create_sess_files+0x18f/0x1f0 [rtrs_server]
> > ? __alloc_pages_nodemask+0x16c/0x2b0
> > ? kmalloc_order+0x7c/0x90
> > ? kmalloc_order_trace+0x1d/0xa0
> > ? rtrs_iu_alloc+0x17e/0x1bf [rtrs_core]
> > rtrs_srv_info_req_done+0x417/0x5b0 [rtrs_server]
> > ? __switch_to_asm+0x40/0x70
> > __ib_process_cq+0x76/0xd0 [ib_core]
> > ib_cq_poll_work+0x26/0x80 [ib_core]
> > process_one_work+0x1df/0x3a0
> > worker_thread+0x4a/0x3c0
> > kthread+0xfb/0x130
> > ? process_one_work+0x3a0/0x3a0
> > ? kthread_park+0x90/0x90
> > ret_from_fork+0x1f/0x40
> > kobject_add_internal failed for ctl with -EEXIST, don't try to register things with the same name in the same directory.
> > rtrs_server L178: device_add(): -17
> >
> > This patch checks the path name and disconnect on server to prevent
> > the kernel error.
> >
> > Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
> > Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
> > ---
> >  drivers/infiniband/ulp/rtrs/rtrs-srv.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/infiniband/ulp/rtrs/rtrs-srv.c b/drivers/infiniband/ulp/rtrs/rtrs-srv.c
> > index cd9a4ccf4c28..b814a6052cf1 100644
> > --- a/drivers/infiniband/ulp/rtrs/rtrs-srv.c
> > +++ b/drivers/infiniband/ulp/rtrs/rtrs-srv.c
> > @@ -758,6 +758,14 @@ static bool exist_sessname(struct rtrs_srv_ctx *ctx,
> >       struct rtrs_srv_sess *sess;
> >       bool found = false;
> >
> > +     /*
> > +      * Session name "ct" is not allowed because
> > +      * /sys/devices/virtual/rtrs-server/ctl already exists
> > +      * for setup management.
> > +      */
> > +     if (!strcmp(sessname, "ctl"))
> > +             return true;
>
> Why does it have special treatment?

rtrs-server creates a folder named ctl when the module is modprob'ed.
When a session is established, a folder of the session name is created
at the same location, which would hold sysfs entries such as
clt_hostname, path details, queue_depth, etc.

Due to this conflict of names, creation of session with that name is
not possible. So this gracefully fails the connection establishment
instead of a stack trace.

> And what will happen if user supplies "." or ".."?

Weirdly enough, this succeeds. I tried, and the session creation
succeeds, and there is a hidden entry in the rtrs-server folder, but
it cannot be accessed through bash.

> Does rtrs receive this session name from the other side in the network?

Yes. This string is entered by the user while creating the session.

>
> Thanks