Re: [PATCH v3 1/1] net:rds: Fix possible deadlock in rds_message_put

[Allison Henderson <allison.henderson@oracle.com>]

On Thu, 2024-02-08 at 15:37 +0800, Zhu Yanjun wrote:
> 在 2024/2/8 7:38, allison.henderson@oracle.com 写道:
> > From: Allison Henderson <allison.henderson@oracle.com>
> > 
> > Functions rds_still_queued and rds_clear_recv_queue lock a given
> > socket
> > in order to safely iterate over the incoming rds messages. However
> > calling rds_inc_put while under this lock creates a potential
> > deadlock.
> > rds_inc_put may eventually call rds_message_purge, which will lock
> > m_rs_lock. This is the incorrect locking order since m_rs_lock is
> > meant to be locked before the socket. To fix this, we move the
> > message
> > item to a local list or variable that wont need rs_recv_lock
> > protection.
> > Then we can safely call rds_inc_put on any item stored locally
> > after
> > rs_recv_lock is released.
> > 
> > Fixes: bdbe6fbc6a2f (RDS: recv.c)
> 
> A trivial problem,
> Based on the file 
> https://urldefense.com/v3/__https://www.kernel.org/doc/Documentation/process/submitting-patches.rst__;!!ACWV5N9M2RV99hQ!MiEeS6J7X92LD8hhF5jHl882A8vJtDEXfxPdBG3cmE7Qhsic--cSQKgEbPDF1W-i_ZXdM64n5coFpc1xEIOZWmFhoubN$
>  ,
> Fixes tag should be the following?
> 
> Fixes: bdbe6fbc6a2f ("RDS: recv.c")

Ah, I had missed the quotations.  Will update.  Thanks for the review!

Allison

> 
> Thanks,
> Zhu Yanjun
> 
> > Reported-by: syzbot+f9db6ff27b9bfdcfeca0@syzkaller.appspotmail.com
> > Reported-by: syzbot+dcd73ff9291e6d34b3ab@syzkaller.appspotmail.com
> > 
> > Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
> > ---
> >   net/rds/recv.c | 13 +++++++++++--
> >   1 file changed, 11 insertions(+), 2 deletions(-)
> > 
> > diff --git a/net/rds/recv.c b/net/rds/recv.c
> > index c71b923764fd..5627f80013f8 100644
> > --- a/net/rds/recv.c
> > +++ b/net/rds/recv.c
> > @@ -425,6 +425,7 @@ static int rds_still_queued(struct rds_sock
> > *rs, struct rds_incoming *inc,
> >         struct sock *sk = rds_rs_to_sk(rs);
> >         int ret = 0;
> >         unsigned long flags;
> > +       struct rds_incoming *to_drop = NULL;
> >   
> >         write_lock_irqsave(&rs->rs_recv_lock, flags);
> >         if (!list_empty(&inc->i_item)) {
> > @@ -435,11 +436,14 @@ static int rds_still_queued(struct rds_sock
> > *rs, struct rds_incoming *inc,
> >                                               -be32_to_cpu(inc-
> > >i_hdr.h_len),
> >                                               inc->i_hdr.h_dport);
> >                         list_del_init(&inc->i_item);
> > -                       rds_inc_put(inc);
> > +                       to_drop = inc;
> >                 }
> >         }
> >         write_unlock_irqrestore(&rs->rs_recv_lock, flags);
> >   
> > +       if (to_drop)
> > +               rds_inc_put(to_drop);
> > +
> >         rdsdebug("inc %p rs %p still %d dropped %d\n", inc, rs,
> > ret, drop);
> >         return ret;
> >   }
> > @@ -758,16 +762,21 @@ void rds_clear_recv_queue(struct rds_sock
> > *rs)
> >         struct sock *sk = rds_rs_to_sk(rs);
> >         struct rds_incoming *inc, *tmp;
> >         unsigned long flags;
> > +       LIST_HEAD(to_drop);
> >   
> >         write_lock_irqsave(&rs->rs_recv_lock, flags);
> >         list_for_each_entry_safe(inc, tmp, &rs->rs_recv_queue,
> > i_item) {
> >                 rds_recv_rcvbuf_delta(rs, sk, inc->i_conn->c_lcong,
> >                                       -be32_to_cpu(inc-
> > >i_hdr.h_len),
> >                                       inc->i_hdr.h_dport);
> > +               list_move(&inc->i_item, &to_drop);
> > +       }
> > +       write_unlock_irqrestore(&rs->rs_recv_lock, flags);
> > +
> > +       list_for_each_entry_safe(inc, tmp, &to_drop, i_item) {
> >                 list_del_init(&inc->i_item);
> >                 rds_inc_put(inc);
> >         }
> > -       write_unlock_irqrestore(&rs->rs_recv_lock, flags);
> >   }
> >   
> >   /*
>