On Thu, Jun 29, 2023 at 6:45 AM Winston Wen <wentao@xxxxxxxxxxxxx> wrote:
>
> Hi Steve,
>
> On Wed, 28 Jun 2023 12:16:09 -0500
> Steve French <smfrench@xxxxxxxxx> wrote:
>
> > 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.
>
> With Shyam's updated patch, It is expected that no
> existing session would be found in the list, so the check of session
> state is no longer strictly necessary now, but don't hurt.
>
> So we have 2 choices in scanning the list:
> - do the check. (patch 2/3, merged)
> - remove the check and add a warning. (this new patch)
>
> If you find the latter to be better, you have the option to replace the
> original two patches with this new one.
>
> Alternatively, you can simply disregard the new patch and take no
> action, as the patch 2/3 has already been merged into the for-next
> branch. (This may be a better choice for now, but I don't have a strong
> opinion on this, both are okay to me.)
>
> Really sorry for my poor English and the lack of clarity in my
> explanation.
>
> >
> > 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,
> Winston
Hi Winston/Steve,
It turns out that my patch above has a problem.
For logoff to work, we need the session in the smb_ses_list.
So I think Winston's patch series here make sense.
@Winston Wen We may need similar checks for SES_EXITING in other
places where we iterate smb_ses_list.
Can you see if all the places are covered and send additional patches if needed?
If you do not get to it in a few days, I can do it myself.
Thanks for these patches. Keep them coming. :)
--
Regards,
Shyam
