Re: [PATCH 3/3] net/vdev: fix insert vdev core dump

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 3/14/2024 10:36 AM, Mingjin Ye wrote:
> Inserting a vdev device when the device arguments are already stored
> in devargs_list, the rte_devargs_insert function replaces the supplied
> new devargs with the found devargs and frees the new devargs. As a
> result, the use of free devargs results in a core dump.
> 
> This patch fixes the issue by using valid devargs.
> 
> Fixes: f3a1188cee4a ("devargs: make device representation generic")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Mingjin Ye <mingjinx.ye@intel.com>

I am not too familiar with how devargs works, so I have a trivial question.

I understand the point of this patch, and it is roughly as follows:

1) we enter insert_vdev and allocated new devargs structure (and copy 
the `name` into devargs)
2) we set dev->device.name to devargs->name
3) we insert devargs into the list using rte_devargs_insert
4) if devargs list already had devargs with the same name, our devargs 
is destroyed and replaced with devargs that is in the list
5) because of this, dev->device.name becomes invalid as that specific 
devargs has been freed - it points to name from the old devargs

We do need to store devargs->name in dev->device.name, and we need to do 
so after calling rte_devargs_insert to avoid keeping reference to memory 
that was freed. So, provisionally,

Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>

My question is, under what circumstances would there be duplicate 
entries in devargs list? I assume there is an answer to that question 
because rte_devargs_insert() expects this case, so this is just for my 
understanding - I can't seem to figure out how we would arrive at a 
situation where we have duplicate devargs.

> ---
>   drivers/bus/vdev/vdev.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/vdev/vdev.c b/drivers/bus/vdev/vdev.c
> index 1a6cc7d12d..53fc4a6e21 100644
> --- a/drivers/bus/vdev/vdev.c
> +++ b/drivers/bus/vdev/vdev.c
> @@ -286,7 +286,6 @@ insert_vdev(const char *name, const char *args, struct rte_vdev_device **p_dev)
>   
>   	dev->device.bus = &rte_vdev_bus;
>   	dev->device.numa_node = SOCKET_ID_ANY;
> -	dev->device.name = devargs->name;
>   
>   	if (find_vdev(name)) {
>   		/*
> @@ -300,6 +299,7 @@ insert_vdev(const char *name, const char *args, struct rte_vdev_device **p_dev)
>   
>   	rte_devargs_insert(&devargs);
>   	dev->device.devargs = devargs;
> +	dev->device.name = devargs->name;
>   	TAILQ_INSERT_TAIL(&vdev_device_list, dev, next);
>   
>   	if (p_dev)

-- 
Thanks,
Anatoly