this didn't apply (merge conflict with Shyam's updated patch) - can
you update it based on for-next and resend
Also let me know if you see other patches missing.
On Tue, Jun 27, 2023 at 8:55 PM Winston Wen <wentao@xxxxxxxxxxxxx> wrote:
>
> On Wed, 28 Jun 2023 08:43:33 +0800
> Winston Wen <wentao@xxxxxxxxxxxxx> wrote:
>
> > On Tue, 27 Jun 2023 17:43:25 +0530
> > Shyam Prasad N <nspmangalore@xxxxxxxxx> wrote:
> >
> > > On Tue, Jun 27, 2023 at 1:04 PM Winston Wen <wentao@xxxxxxxxxxxxx>
> > > wrote:
> > > >
> > > > On Tue, 27 Jun 2023 12:24:04 +0530
> > > > Shyam Prasad N <nspmangalore@xxxxxxxxx> wrote:
> > > >
> > > > > On Mon, Jun 26, 2023 at 2:09 PM Winston Wen
> > > > > <wentao@xxxxxxxxxxxxx> wrote:
> > > > > >
> > > > > > On Mon, 26 Jun 2023 12:24:35 +0530
> > > > > > Shyam Prasad N <nspmangalore@xxxxxxxxx> wrote:
> > > > > >
> > > > > > > On Mon, Jun 26, 2023 at 10:54 AM Steve French
> > > > > > > <smfrench@xxxxxxxxx> wrote:
> > > > > > > >
> > > > > > > > Added Cc: stable and Shyam's RB and merged into
> > > > > > > > cifs-2.6.git for-next
> > > > > > > >
> > > > > > > > On Mon, Jun 26, 2023 at 12:15 AM Shyam Prasad N
> > > > > > > > <nspmangalore@xxxxxxxxx> wrote:
> > > > > > > > >
> > > > > > > > > On Mon, Jun 26, 2023 at 9:25 AM Winston Wen
> > > > > > > > > <wentao@xxxxxxxxxxxxx> wrote:
> > > > > > > > > >
> > > > > > > > > > We switch session state to SES_EXITING without
> > > > > > > > > > cifs_tcp_ses_lock now, it may lead to potential
> > > > > > > > > > use-after-free issue.
> > > > > > > > > >
> > > > > > > > > > Consider the following execution processes:
> > > > > > > > > >
> > > > > > > > > > Thread 1:
> > > > > > > > > > __cifs_put_smb_ses()
> > > > > > > > > > spin_lock(&cifs_tcp_ses_lock)
> > > > > > > > > > if (--ses->ses_count > 0)
> > > > > > > > > > spin_unlock(&cifs_tcp_ses_lock)
> > > > > > > > > > return
> > > > > > > > > > spin_unlock(&cifs_tcp_ses_lock)
> > > > > > > > > > ---> **GAP**
> > > > > > > > > > spin_lock(&ses->ses_lock)
> > > > > > > > > > if (ses->ses_status == SES_GOOD)
> > > > > > > > > > ses->ses_status = SES_EXITING
> > > > > > > > > > spin_unlock(&ses->ses_lock)
> > > > > > > > > >
> > > > > > > > > > Thread 2:
> > > > > > > > > > cifs_find_smb_ses()
> > > > > > > > > > spin_lock(&cifs_tcp_ses_lock)
> > > > > > > > > > list_for_each_entry(ses, ...)
> > > > > > > > > > spin_lock(&ses->ses_lock)
> > > > > > > > > > if (ses->ses_status == SES_EXITING)
> > > > > > > > > > spin_unlock(&ses->ses_lock)
> > > > > > > > > > continue
> > > > > > > > > > ...
> > > > > > > > > > spin_unlock(&ses->ses_lock)
> > > > > > > > > > if (ret)
> > > > > > > > > > cifs_smb_ses_inc_refcount(ret)
> > > > > > > > > > spin_unlock(&cifs_tcp_ses_lock)
> > > > > > > > > >
> > > > > > > > > > If thread 1 is preempted in the gap and thread 2 start
> > > > > > > > > > executing, thread 2 will get the session, and soon
> > > > > > > > > > thread 1 will switch the session state to SES_EXITING
> > > > > > > > > > and start releasing it, even though thread 1 had
> > > > > > > > > > increased the session's refcount and still uses it.
> > > > > > > > > >
> > > > > > > > > > So switch session state under cifs_tcp_ses_lock to
> > > > > > > > > > eliminate this gap.
> > > > > > > > > >
> > > > > > > > > > Signed-off-by: Winston Wen <wentao@xxxxxxxxxxxxx>
> > > > > > > > > > ---
> > > > > > > > > > fs/smb/client/connect.c | 7 ++++---
> > > > > > > > > > 1 file changed, 4 insertions(+), 3 deletions(-)
> > > > > > > > > >
> > > > > > > > > > diff --git a/fs/smb/client/connect.c
> > > > > > > > > > b/fs/smb/client/connect.c index
> > > > > > > > > > 9d16626e7a66..165ecb222c19 100644 ---
> > > > > > > > > > a/fs/smb/client/connect.c +++
> > > > > > > > > > b/fs/smb/client/connect.c @@ -1963,15 +1963,16 @@
> > > > > > > > > > void __cifs_put_smb_ses(struct cifs_ses *ses)
> > > > > > > > > > spin_unlock(&cifs_tcp_ses_lock); return;
> > > > > > > > > > }
> > > > > > > > > > + spin_lock(&ses->ses_lock);
> > > > > > > > > > + if (ses->ses_status == SES_GOOD)
> > > > > > > > > > + ses->ses_status = SES_EXITING;
> > > > > > > > > > + spin_unlock(&ses->ses_lock);
> > > > > > > > > > spin_unlock(&cifs_tcp_ses_lock);
> > > > > > > > > >
> > > > > > > > > > /* ses_count can never go negative */
> > > > > > > > > > WARN_ON(ses->ses_count < 0);
> > > > > > > > > >
> > > > > > > > > > spin_lock(&ses->ses_lock);
> > > > > > > > > > - if (ses->ses_status == SES_GOOD)
> > > > > > > > > > - ses->ses_status = SES_EXITING;
> > > > > > > > > > -
> > > > > > > > > > if (ses->ses_status == SES_EXITING &&
> > > > > > > > > > server->ops->logoff) { spin_unlock(&ses->ses_lock);
> > > > > > > > > > cifs_free_ipc(ses);
> > > > > > > > > > --
> > > > > > > > > > 2.40.1
> > > > > > > > > >
> > > > > > > > >
> > > > > > > > > Good catch.
> > > > > > > > > Looks good to me.
> > > > > > > > > @Steve French Please CC stable for this one.
> > > > > > > > >
> > > > > > > > > --
> > > > > > > > > Regards,
> > > > > > > > > Shyam
> > > > > > > >
> > > > > > > >
> > > > > > > >
> > > > > > > > --
> > > > > > > > Thanks,
> > > > > > > >
> > > > > > > > Steve
> > > > > > >
> > > > > > > @Winston Wen I think the following change should be
> > > > > > > sufficient to fix this issue:
> > > > > > > diff --git a/fs/smb/client/connect.c
> > > > > > > b/fs/smb/client/connect.c index 9d16626e7a66..78874eb2537d
> > > > > > > 100644 --- a/fs/smb/client/connect.c
> > > > > > > +++ b/fs/smb/client/connect.c
> > > > > > > @@ -1963,10 +1963,11 @@ void __cifs_put_smb_ses(struct
> > > > > > > cifs_ses *ses) spin_unlock(&cifs_tcp_ses_lock);
> > > > > > > return;
> > > > > > > }
> > > > > > > - spin_unlock(&cifs_tcp_ses_lock);
> > > > > > >
> > > > > > > /* ses_count can never go negative */
> > > > > > > WARN_ON(ses->ses_count < 0);
> > > > > > > + list_del_init(&ses->smb_ses_list);
> > > > > > > + spin_unlock(&cifs_tcp_ses_lock);
> > > > > > >
> > > > > > > spin_lock(&ses->ses_lock);
> > > > > > > if (ses->ses_status == SES_GOOD)
> > > > > > > @@ -1986,9 +1987,6 @@ void __cifs_put_smb_ses(struct
> > > > > > > cifs_ses *ses) cifs_free_ipc(ses);
> > > > > > > }
> > > > > > >
> > > > > > > - spin_lock(&cifs_tcp_ses_lock);
> > > > > > > - list_del_init(&ses->smb_ses_list);
> > > > > > > - spin_unlock(&cifs_tcp_ses_lock);
> > > > > > >
> > > > > > > chan_count = ses->chan_count;
> > > > > > >
> > > > > > > The bug was that the ses was kept in the smb ses list, even
> > > > > > > after the ref count had reached 0.
> > > > > > > With the above change, that should be fixed, and no one
> > > > > > > should be able to get to the ses from that point.
> > > > > > >
> > > > > > > Please let me know if you see a problem with this.
> > > > > > >
> > > > > >
> > > > > > Hi Shyam,
> > > > > >
> > > > > > Thanks for the comments! And sorry for my late reply...
> > > > > >
> > > > > > It make sense to me that maybe we should remove the session
> > > > > > from the list once its refcount is reduced to 0 to avoid any
> > > > > > futher access. In fact, I did try to do this from the
> > > > > > beginning. But I was not sure if we need to access the session
> > > > > > from the list in the free process, such as the following:
> > > > > >
> > > > > > smb2_check_receive()
> > > > > > smb2_verify_signature()
> > > > > > server->ops->calc_signature()
> > > > > > smb2_calc_signature()
> > > > > > smb2_find_smb_ses()
> > > > > > /* scan the list and find the session */
> > > > > >
> > > > > > Perhaps we need some refactoring here.
> > > > >
> > > > > Yes. The above ses finding is expected to fail during a
> > > > > reconnect.
> > > >
> > > > Agreed.
> > > >
> > > > >
> > > > > >
> > > > > > So I gave up on this approach and did a small fix to make it
> > > > > > work, but maybe I missed something elsewhere...
> > > > > >
> > > > > >
> > > > > > --
> > > > > > Thanks,
> > > > > > Winston
> > > > >
> > > > > Attaching the above change as a patch.
> > > > > It replaces this particular patch in the series.
> > > >
> > > > I think this is a better way to fix the problem, the session
> > > > really should not stay in the list and be found after it has been
> > > > marked EXITING.
> > > >
> > > > >
> > > > > The other two patches are not strictly necessary with this
> > > > > change, but don't hurt.
> > > > >
> > > >
> > > > Yes. Feel free to drop them if they are not necessary. And if
> > > > that's the case, perhaps we should do some cleaning work on other
> > > > paths to ensure consistency.
> > >
> > > I don't really have a strong opinion about this. Even if they stay,
> > > I'm okay. But curious to know what you mean by the cleaning work on
> > > other paths here. Do you still think there's more cleanup needed
> > > around this?
> >
> > IIRC there are other paths that scan the list and do the
> > check, like cifs_find_smb_ses(). So I think if they become unnecessary
> > now after this fix patch, maybe we can also remove them at the same
> > time to avoid make others confused.
> >
> > But I also don't have a strong opinion about this. I think we have the
> > following options and all are okay to me. Which one do you prefer?
> >
> > - keep/add the check
> > - remove all checks
> > - remove all checks and add a WARNING
> >
> > (I think we shouldn't find a exiting session in the list now.)
> >
> > >
> > > >
> > > > Thanks for your review and comments!
> > > >
> > > > >
> > > > > --
> > > > > Regards,
> > > > > Shyam
> > > >
> > > >
> > > > --
> > > > Thanks,
> > > > Winston
> > >
> > >
> > >
> >
> >
> >
>
> Attaching the patch (remove all checks and add a warning)
>
> --
> Thanks,
> Winston
--
Thanks,
Steve
