netdev - [PATCH 2/2] net: ipv4: Fix a possible null-pointer dereference in fib4_rule

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Date:   Fri, 26 Jul 2019 10:25:04 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     davem@...emloft.net, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH 2/2] net: ipv4: Fix a possible null-pointer dereference in fib4_rule_suppress()

In fib4_rule_suppress(), there is an if statement on line 145 to check
whether result->fi is NULL:
    if (result->fi)

When result->fi is NULL, it is used on line 167:
    fib_info_put(result->fi);

In fib_info_put(), the argument fi is used:
    if (refcount_dec_and_test(&fi->fib_clntref))

Thus, a possible null-pointer dereference may occur.

To fix this bug, result->fi is checked before calling fib_info_put().

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 net/ipv4/fib_rules.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c
index b43a7ba5c6a4..daedce293aab 100644
--- a/net/ipv4/fib_rules.c
+++ b/net/ipv4/fib_rules.c
@@ -163,7 +163,7 @@ static bool fib4_rule_suppress(struct fib_rule *rule, struct fib_lookup_arg *arg
 	return false;
 
 suppress_route:
-	if (!(arg->flags & FIB_LOOKUP_NOREF))
+	if (!(arg->flags & FIB_LOOKUP_NOREF) && result->fi)
 		fib_info_put(result->fi);
 	return true;
 }
-- 
2.17.0