netdev - Re: [PATCH][V2] net: bridge: remove redundant checks for null p->dev and p->br

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Date:   Sun, 25 Nov 2018 10:26:07 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     colin.king@...onical.com
Cc:     roopa@...ulusnetworks.com, nikolay@...ulusnetworks.com,
        bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][V2] net: bridge: remove redundant checks for null
 p->dev and p->br

From: Colin King <colin.king@...onical.com>
Date: Sun, 25 Nov 2018 16:08:51 +0000

> From: Colin Ian King <colin.king@...onical.com>
> 
> 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@...onical.com>

Applied.