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

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Date:   Sun, 25 Nov 2018 16:08:51 +0000
From:   Colin King <colin.king@...onical.com>
To:     Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        "David S . Miller" <davem@...emloft.net>,
        bridge@...ts.linux-foundation.org, netdev@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][V2] net: bridge: remove redundant checks for null p->dev and p->br

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>

---

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;
 
-- 
2.19.1