linux-kernel - [ 010/135] net: fib: fib6_add: fix potential NULL pointer dereference

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Message-Id: <20131011193946.347613112@linuxfoundation.org>
Date:	Fri, 11 Oct 2013 12:38:11 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Daniel Borkmann <dborkman@...hat.com>,
	Lin Ming <mlin@...pku.edu.cn>,
	Matti Vaittinen <matti.vaittinen@....com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 010/135] net: fib: fib6_add: fix potential NULL pointer dereference

3.11-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Borkmann <dborkman@...hat.com>

[ Upstream commit ae7b4e1f213aa659aedf9c6ecad0bf5f0476e1e2 ]

When the kernel is compiled with CONFIG_IPV6_SUBTREES, and we return
with an error in fn = fib6_add_1(), then error codes are encoded into
the return pointer e.g. ERR_PTR(-ENOENT). In such an error case, we
write the error code into err and jump to out, hence enter the if(err)
condition. Now, if CONFIG_IPV6_SUBTREES is enabled, we check for:

  if (pn != fn && pn->leaf == rt)
    ...
  if (pn != fn && !pn->leaf && !(pn->fn_flags & RTN_RTINFO))
    ...

Since pn is NULL and fn is f.e. ERR_PTR(-ENOENT), then pn != fn
evaluates to true and causes a NULL-pointer dereference on further
checks on pn. Fix it, by setting both NULL in error case, so that
pn != fn already evaluates to false and no further dereference
takes place.

This was first correctly implemented in 4a287eba2 ("IPv6 routing,
NLM_F_* flag support: REPLACE and EXCL flags support, warn about
missing CREATE flag"), but the bug got later on introduced by
188c517a0 ("ipv6: return errno pointers consistently for fib6_add_1()").

Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
Cc: Lin Ming <mlin@...pku.edu.cn>
Cc: Matti Vaittinen <matti.vaittinen@....com>
Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
Acked-by: Matti Vaittinen <matti.vaittinen@....com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv6/ip6_fib.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -825,9 +825,9 @@ int fib6_add(struct fib6_node *root, str
 	fn = fib6_add_1(root, &rt->rt6i_dst.addr, sizeof(struct in6_addr),
 			rt->rt6i_dst.plen, offsetof(struct rt6_info, rt6i_dst),
 			allow_create, replace_required);
-
 	if (IS_ERR(fn)) {
 		err = PTR_ERR(fn);
+		fn = NULL;
 		goto out;
 	}

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