2021-04-07 13:43:12

by Aditya Pakki

[permalink] [raw]
Subject: [PATCH] SUNRPC: Add a check for gss_release_msg

In gss_pipe_destroy_msg(), in case of error in msg, gss_release_msg
deletes gss_msg. The patch adds a check to avoid a potential double
free.

Signed-off-by: Aditya Pakki <[email protected]>
---
net/sunrpc/auth_gss/auth_gss.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 5f42aa5fc612..eb52eebb3923 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -848,7 +848,8 @@ gss_pipe_destroy_msg(struct rpc_pipe_msg *msg)
warn_gssd();
gss_release_msg(gss_msg);
}
- gss_release_msg(gss_msg);
+ if (gss_msg)
+ gss_release_msg(gss_msg);
}

static void gss_pipe_dentry_destroy(struct dentry *dir,
--
2.25.1


2021-04-07 21:20:23

by [email protected]

[permalink] [raw]
Subject: Re: [PATCH] SUNRPC: Add a check for gss_release_msg

On Tue, Apr 06, 2021 at 07:16:56PM -0500, Aditya Pakki wrote:
> In gss_pipe_destroy_msg(), in case of error in msg, gss_release_msg
> deletes gss_msg. The patch adds a check to avoid a potential double
> free.

We're already dereferenced msg. Nothing has set gss_msg to NULL. It's
the gss_msg->count reference count that's supposed to prevent double
frees.

Did you see an actual bug or warning from some tool, and if so, could
you share the details?

--b.

>
> Signed-off-by: Aditya Pakki <[email protected]>
> ---
> net/sunrpc/auth_gss/auth_gss.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
> index 5f42aa5fc612..eb52eebb3923 100644
> --- a/net/sunrpc/auth_gss/auth_gss.c
> +++ b/net/sunrpc/auth_gss/auth_gss.c
> @@ -848,7 +848,8 @@ gss_pipe_destroy_msg(struct rpc_pipe_msg *msg)
> warn_gssd();
> gss_release_msg(gss_msg);
> }
> - gss_release_msg(gss_msg);
> + if (gss_msg)
> + gss_release_msg(gss_msg);
> }
>
> static void gss_pipe_dentry_destroy(struct dentry *dir,
> --
> 2.25.1

2021-04-08 15:01:49

by Trond Myklebust

[permalink] [raw]
Subject: Re: [PATCH] SUNRPC: Add a check for gss_release_msg

On Tue, 2021-04-06 at 19:16 -0500, Aditya Pakki wrote:
> In gss_pipe_destroy_msg(), in case of error in msg, gss_release_msg
> deletes gss_msg. The patch adds a check to avoid a potential double
> free.
>
> Signed-off-by: Aditya Pakki <[email protected]>
> ---
>  net/sunrpc/auth_gss/auth_gss.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/sunrpc/auth_gss/auth_gss.c
> b/net/sunrpc/auth_gss/auth_gss.c
> index 5f42aa5fc612..eb52eebb3923 100644
> --- a/net/sunrpc/auth_gss/auth_gss.c
> +++ b/net/sunrpc/auth_gss/auth_gss.c
> @@ -848,7 +848,8 @@ gss_pipe_destroy_msg(struct rpc_pipe_msg *msg)
>                         warn_gssd();
>                 gss_release_msg(gss_msg);
>         }
> -       gss_release_msg(gss_msg);
> +       if (gss_msg)
> +               gss_release_msg(gss_msg);
>  }
>  
>  static void gss_pipe_dentry_destroy(struct dentry *dir,


NACK. There's no double free there.

--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
[email protected]


2021-04-08 15:25:42

by Olga Kornievskaia

[permalink] [raw]
Subject: Re: [PATCH] SUNRPC: Add a check for gss_release_msg

On Thu, Apr 8, 2021 at 11:01 AM Trond Myklebust <[email protected]> wrote:
>
> On Tue, 2021-04-06 at 19:16 -0500, Aditya Pakki wrote:
> > In gss_pipe_destroy_msg(), in case of error in msg, gss_release_msg
> > deletes gss_msg. The patch adds a check to avoid a potential double
> > free.
> >
> > Signed-off-by: Aditya Pakki <[email protected]>
> > ---
> > net/sunrpc/auth_gss/auth_gss.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/sunrpc/auth_gss/auth_gss.c
> > b/net/sunrpc/auth_gss/auth_gss.c
> > index 5f42aa5fc612..eb52eebb3923 100644
> > --- a/net/sunrpc/auth_gss/auth_gss.c
> > +++ b/net/sunrpc/auth_gss/auth_gss.c
> > @@ -848,7 +848,8 @@ gss_pipe_destroy_msg(struct rpc_pipe_msg *msg)
> > warn_gssd();
> > gss_release_msg(gss_msg);
> > }
> > - gss_release_msg(gss_msg);
> > + if (gss_msg)
> > + gss_release_msg(gss_msg);
> > }
> >
> > static void gss_pipe_dentry_destroy(struct dentry *dir,
>
>
> NACK. There's no double free there.

I disagree that there is no double free, the wording of the commit
describes the problem in the error case is that we call
gss_release_msg() and then we call it again but the 1st one released
the gss_msg. However, I think the fix should probably be instead:
diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 5f42aa5fc612..e8aae617e981 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -846,7 +846,7 @@ gss_pipe_destroy_msg(struct rpc_pipe_msg *msg)
gss_unhash_msg(gss_msg);
if (msg->errno == -ETIMEDOUT)
warn_gssd();
- gss_release_msg(gss_msg);
+ return gss_release_msg(gss_msg);
}
gss_release_msg(gss_msg);
}

>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> [email protected]
>
>

2021-04-08 16:03:16

by Trond Myklebust

[permalink] [raw]
Subject: Re: [PATCH] SUNRPC: Add a check for gss_release_msg

On Thu, 2021-04-08 at 11:24 -0400, Olga Kornievskaia wrote:
> On Thu, Apr 8, 2021 at 11:01 AM Trond Myklebust <
> [email protected]> wrote:
> >
> > On Tue, 2021-04-06 at 19:16 -0500, Aditya Pakki wrote:
> > > In gss_pipe_destroy_msg(), in case of error in msg,
> > > gss_release_msg
> > > deletes gss_msg. The patch adds a check to avoid a potential
> > > double
> > > free.
> > >
> > > Signed-off-by: Aditya Pakki <[email protected]>
> > > ---
> > >  net/sunrpc/auth_gss/auth_gss.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/net/sunrpc/auth_gss/auth_gss.c
> > > b/net/sunrpc/auth_gss/auth_gss.c
> > > index 5f42aa5fc612..eb52eebb3923 100644
> > > --- a/net/sunrpc/auth_gss/auth_gss.c
> > > +++ b/net/sunrpc/auth_gss/auth_gss.c
> > > @@ -848,7 +848,8 @@ gss_pipe_destroy_msg(struct rpc_pipe_msg
> > > *msg)
> > >                         warn_gssd();
> > >                 gss_release_msg(gss_msg);
> > >         }
> > > -       gss_release_msg(gss_msg);
> > > +       if (gss_msg)
> > > +               gss_release_msg(gss_msg);
> > >  }
> > >
> > >  static void gss_pipe_dentry_destroy(struct dentry *dir,
> >
> >
> > NACK. There's no double free there.
>
> I disagree that there is no double free, the wording of the commit
> describes the problem in the error case is that we call
> gss_release_msg() and then we call it again but the 1st one released
> the gss_msg. However, I think the fix should probably be instead:
> diff --git a/net/sunrpc/auth_gss/auth_gss.c
> b/net/sunrpc/auth_gss/auth_gss.c
> index 5f42aa5fc612..e8aae617e981 100644
> --- a/net/sunrpc/auth_gss/auth_gss.c
> +++ b/net/sunrpc/auth_gss/auth_gss.c
> @@ -846,7 +846,7 @@ gss_pipe_destroy_msg(struct rpc_pipe_msg *msg)
>                 gss_unhash_msg(gss_msg);
>                 if (msg->errno == -ETIMEDOUT)
>                         warn_gssd();
> -               gss_release_msg(gss_msg);
> +               return gss_release_msg(gss_msg);
>         }
>         gss_release_msg(gss_msg);
>  }
>
Please look one line further up: there is a refcount_inc() that matches
that first gss_release_msg(). Removing that call results in a
reintroduction of the leak that Neil fixed in commit 1cded9d2974fe
("SUNRPC: fix refcounting problems with auth_gss messages.").

We might, however, instead opt to remove both the refcount_inc() and
matching gss_release_msg(). Those do seem to be redundant, given that
the caller also holds a refcount.

> >
> > --
> > Trond Myklebust
> > Linux NFS client maintainer, Hammerspace
> > [email protected]
> >
> >

--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
[email protected]