On Sun, Apr 16, 2017 at 01:34:22PM +0530, Sumit Semwal wrote:
> Hi Greg,
>
>
>
> On Apr 16, 2017 13:29, "Greg KH" <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, Apr 12, 2017 at 11:13:38PM +0530, Sumit Semwal wrote:
> > From: NeilBrown <neilb@xxxxxxxx>
> >
> > [ Upstream commit 1cded9d2974fe4fe339fc0ccd6638b80d465ab2c ]
> >
> > There are two problems with refcounting of auth_gss messages.
> >
> > First, the reference on the pipe->pipe list (taken by a call
> > to rpc_queue_upcall()) is not counted. It seems to be
> > assumed that a message in pipe->pipe will always also be in
> > pipe->in_downcall, where it is correctly reference counted.
> >
> > However there is no guaranty of this. I have a report of a
> > NULL dereferences in rpc_pipe_read() which suggests a msg
> > that has been freed is still on the pipe->pipe list.
> >
> > One way I imagine this might happen is:
> > - message is queued for uid=U and auth->service=S1
> > - rpc.gssd reads this message and starts processing.
> > This removes the message from pipe->pipe
> > - message is queued for uid=U and auth->service=S2
> > - rpc.gssd replies to the first message. gss_pipe_downcall()
> > calls __gss_find_upcall(pipe, U, NULL) and it finds the
> > *second* message, as new messages are placed at the head
> > of ->in_downcall, and the service type is not checked.
> > - This second message is removed from ->in_downcall and freed
> > by gss_release_msg() (even though it is still on pipe->pipe)
> > - rpc.gssd tries to read another message, and dereferences a pointer
> > to this message that has just been freed.
> >
> > I fix this by incrementing the reference count before calling
> > rpc_queue_upcall(), and decrementing it if that fails, or normally in
> > gss_pipe_destroy_msg().
> >
> > It seems strange that the reply doesn't target the message more
> > precisely, but I don't know all the details. In any case, I think the
> > reference counting irregularity became a measureable bug when the
> > extra arg was added to __gss_find_upcall(), hence the Fixes: line
> > below.
> >
> > The second problem is that if rpc_queue_upcall() fails, the new
> > message is not freed. gss_alloc_msg() set the ->count to 1,
> > gss_add_msg() increments this to 2, gss_unhash_msg() decrements to 1,
> > then the pointer is discarded so the memory never gets freed.
> >
> > Fixes: 9130b8dbc6ac ("SUNRPC: allow for upcalls for same uid but
> different gss service")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1011250
> > Signed-off-by: NeilBrown <neilb@xxxxxxxx>
> > Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> > Signed-off-by: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
> > ---
> > net/sunrpc/auth_gss/auth_gss.c | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
>
> This patch is already in 4.9.2! Something went really wrong with your
> patch selection here, why are you sending patches I already have?
>
> That's true, it's there in 4.9.2, but this patch is marked for 4.4, right?
Doh, that's what I get for working on patches this early, sorry for the
noise...
I'll get to these after this next round of stable kernels go out.
thanks,
greg k-h