netdev - [PATCH net-next 1/2] net: ipv4: remove erroneous advancement of list pointer

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Message-Id: <20190617140228.12523-2-fw@strlen.de>
Date:   Mon, 17 Jun 2019 16:02:27 +0200
From:   Florian Westphal <fw@...len.de>
To:     <netdev@...r.kernel.org>
Cc:     tariqt@...lanox.com, ranro@...lanox.com, maorg@...lanox.com,
        edumazet@...gle.com, Florian Westphal <fw@...len.de>
Subject: [PATCH net-next 1/2] net: ipv4: remove erroneous advancement of list pointer

Causes crash when lifetime expires on an adress as garbage is
dereferenced soon after.

This used to look like this:

 for (ifap = &ifa->ifa_dev->ifa_list;
      *ifap != NULL; ifap = &(*ifap)->ifa_next) {
          if (*ifap == ifa) ...

but this was changed to:

struct in_ifaddr *tmp;

ifap = &ifa->ifa_dev->ifa_list;
tmp = rtnl_dereference(*ifap);
while (tmp) {
   tmp = rtnl_dereference(tmp->ifa_next); // Bogus
   if (rtnl_dereference(*ifap) == ifa) {
     ...
   ifap = &tmp->ifa_next;		// Can be NULL
   tmp = rtnl_dereference(*ifap);	// Dereference
   }
}

Remove the bogus assigment/list entry skip.

Fixes: 2638eb8b50cf ("net: ipv4: provide __rcu annotation for ifa_list")
Signed-off-by: Florian Westphal <fw@...len.de>
---
 net/ipv4/devinet.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 925dffa915cb..914ccc7f192a 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -745,8 +745,7 @@ static void check_lifetime(struct work_struct *work)
 				ifap = &ifa->ifa_dev->ifa_list;
 				tmp = rtnl_dereference(*ifap);
 				while (tmp) {
-					tmp = rtnl_dereference(tmp->ifa_next);
-					if (rtnl_dereference(*ifap) == ifa) {
+					if (tmp == ifa) {
 						inet_del_ifa(ifa->ifa_dev,
 							     ifap, 1);
 						break;
-- 
2.21.0