Re: [PATCH] RDMA/core: fix refcount bug in iwpm_get_nlmsg_request()

[Leon Romanovsky]

On Wed, Sep 02, 2026 at 02:22:13PM +0530, Jeffin Philip wrote:
> iwpm_get_nlmsg_request() initializes refcount _after_ list_add_tail()
> making it accessible to global list where another CPU can kref_get()
> on nlmsg_request causing a refcount "addition on 0" bug. Fix this
> by initializing kref _before_ list_add_tail() so refcount for
> nlmsg_request can be incremented/decremented normally.
> 
> Reported-by: syzbot+bd317784d628820741b5@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=bd317784d628820741b5
> Fixes: 30dc5e63d6a5 ("RDMA/core: Add support for iWARP Port Mapper user space service")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jeffin Philip <jeffinphilip14@xxxxxxxxx>
> ---
>  drivers/infiniband/core/iwpm_util.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/infiniband/core/iwpm_util.c b/drivers/infiniband/core/iwpm_util.c
> index 990cf928b32a..5d07c5756987 100644
> --- a/drivers/infiniband/core/iwpm_util.c
> +++ b/drivers/infiniband/core/iwpm_util.c
> @@ -313,13 +313,13 @@ struct iwpm_nlmsg_request *iwpm_get_nlmsg_request(__u32 nlmsg_seq,
>  	nlmsg_request = kzalloc_obj(struct iwpm_nlmsg_request, gfp);
>  	if (!nlmsg_request)
>  		return NULL;
> +	kref_init(&nlmsg_request->kref);
> +	kref_get(&nlmsg_request->kref);
>  
>  	spin_lock_irqsave(&iwpm_nlmsg_req_lock, flags);
>  	list_add_tail(&nlmsg_request->inprocess_list, &iwpm_nlmsg_req_list);
>  	spin_unlock_irqrestore(&iwpm_nlmsg_req_lock, flags);

These three lines need to be the last in the function, i.e. all fields must
be initialized, not just the refcount.

Thanks

>  
> -	kref_init(&nlmsg_request->kref);
> -	kref_get(&nlmsg_request->kref);
>  	nlmsg_request->nlmsg_seq = nlmsg_seq;
>  	nlmsg_request->nl_client = nl_client;
>  	nlmsg_request->request_done = 0;
> -- 
> 2.55.0
>