2021-10-18 12:39:24

by Thiago Rafael Becker

Subject: [PATCH] sunrpc: bug on rpc_task_set_client when no client is present.

If we pass a NULL client to rpc_task_set_client and no client is
attached to the task, then the kernel will crash later. Antecipate the
crash by checking if a client is available for the task.

Signed-off-by: Thiago Rafael Becker <[email protected]>
---
net/sunrpc/clnt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index f056ff931444..ccbc9a9715da 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -1076,7 +1076,7 @@ void rpc_task_set_transport(struct rpc_task *task, struct rpc_clnt *clnt)
static
void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt)
{
-
+ BUG_ON(clnt == NULL && task->tk_client == NULL);
if (clnt != NULL) {
rpc_task_set_transport(task, clnt);
task->tk_client = clnt;
--
2.31.1

2021-10-20 19:04:58

by Trond Myklebust

Subject: Re: [PATCH] sunrpc: bug on rpc_task_set_client when no client is present.

On Mon, 2021-10-18 at 09:38 -0300, Thiago Rafael Becker wrote:
> If we pass a NULL client to rpc_task_set_client and no client is
> attached to the task, then the kernel will crash later. Antecipate
> the
> crash by checking if a client is available for the task.
>
> Signed-off-by: Thiago Rafael Becker <[email protected]>
> ---
>  net/sunrpc/clnt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> index f056ff931444..ccbc9a9715da 100644
> --- a/net/sunrpc/clnt.c
> +++ b/net/sunrpc/clnt.c
> @@ -1076,7 +1076,7 @@ void rpc_task_set_transport(struct rpc_task
> *task, struct rpc_clnt *clnt)
>  static
>  void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt
> *clnt)
>  {
> -
> +       BUG_ON(clnt == NULL && task->tk_client == NULL);
>         if (clnt != NULL) {
>                 rpc_task_set_transport(task, clnt);
>                 task->tk_client = clnt;


I'm not seeing the point of this BUG_ON(). Why not just change this
code to not check for clnt == NULL, and let the thing Oops when it
tries to dereference clnt?

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

2021-10-20 20:21:07

by Thiago Rafael Becker

Subject: Re: [PATCH] sunrpc: bug on rpc_task_set_client when no client is present.

On Wed, Oct 20, 2021 at 07:04:35PM +0000, Trond Myklebust wrote:
Hello,

> I'm not seeing the point of this BUG_ON(). Why not just change this
> code to not check for clnt == NULL, and let the thing Oops when it
> tries to dereference clnt?

This was changed in 58f9612c6ea85, prior to that, this was not tested. I'm
not sure why this test exists, the only reason I can imagine is to keep
the previous task's rpc_client in case the new client is NULL. Decided
to go conservative on this, and BUG_ON() when no client is available.

Inside the linux source, I don't see how this may happen unless the code
has a bug, so I think it's possible to remove this test.

-- Thiago

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