[3.8.y.z extended stable] Patch "net: fib: fib6_add: fix potential NULL pointer dereference" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    net: fib: fib6_add: fix potential NULL pointer dereference

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.12.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From d7f9494f66659c87e05a2c6b2a735639d17919f9 Mon Sep 17 00:00:00 2001
From: Daniel Borkmann <dborkman at redhat.com>
Date: Sat, 7 Sep 2013 15:13:20 +0200
Subject: net: fib: fib6_add: fix potential NULL pointer dereference

[ 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 at redhat.com>
Cc: Lin Ming <mlin at ss.pku.edu.cn>
Cc: Matti Vaittinen <matti.vaittinen at nsn.com>
Cc: Hannes Frederic Sowa <hannes at stressinduktion.org>
Acked-by: Hannes Frederic Sowa <hannes at stressinduktion.org>
Acked-by: Matti Vaittinen <matti.vaittinen at nsn.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/ipv6/ip6_fib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 7c39aa6..b3adb7f 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -827,9 +827,9 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt, struct nl_info *info)
 	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;
 	}

--
1.8.1.2