On 25/11/2018 18:08, Colin King wrote:
> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>
> A recent change added a null check on p->dev after p->dev was being
> dereferenced by the ns_capable check on p->dev. It turns out that
> neither the p->dev and p->br null checks are necessary, and can be
> removed, which cleans up a static analyis warning.
>
> As Nikolay Aleksandrov noted, these checks can be removed because:
>
> "My reasoning of why it shouldn't be possible:
> - On port add new_nbp() sets both p->dev and p->br before creating
> kobj/sysfs
>
> - On port del (trickier) del_nbp() calls kobject_del() before call_rcu()
> to destroy the port which in turn calls sysfs_remove_dir() which uses
> kernfs_remove() which deactivates (shouldn't be able to open new
> files) and calls kernfs_drain() to drain current open/mmaped files in
> the respective dir before continuing, thus making it impossible to
> open a bridge port sysfs file with p->dev and p->br equal to NULL.
>
> So I think it's safe to remove those checks altogether. It'd be nice to
> get a second look over my reasoning as I might be missing something in
> sysfs/kernfs call path."
>
> Thanks to Nikolay Aleksandrov's suggestion to remove the check and
> David Miller for sanity checking this.
>
> Detected by CoverityScan, CID#751490 ("Dereference before null check")
>
> Fixes: a5f3ea54f3cc ("net: bridge: add support for raw sysfs port options")
> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>
> ---
>
> V2: remove checks instead of moving them before the dereference of
> p->dev.
> ---
> net/bridge/br_sysfs_if.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/net/bridge/br_sysfs_if.c b/net/bridge/br_sysfs_if.c
> index 7c87a2fe5248..88715edb119a 100644
> --- a/net/bridge/br_sysfs_if.c
> +++ b/net/bridge/br_sysfs_if.c
> @@ -320,9 +320,6 @@ static ssize_t brport_store(struct kobject *kobj,
> if (!rtnl_trylock())
> return restart_syscall();
>
> - if (!p->dev || !p->br)
> - goto out_unlock;
> -
> if (brport_attr->store_raw) {
> char *buf_copy;
>
>
Thanks,
Acked-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>
