Bug: Linux Kernel net/fib fib6_add potential NULL pointer dereference ( Ascii Version )

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Linux Kernel net/fib fib6_add potential NULL pointer dereference

Published / (Updated)
Credit
Risk
2013-12-08 / 2013-12-10
PJP
Medium
CWE
CVE
Local
Remote
CWE-264
CVE-2013-6431
No
Yes

CVSS Base Score
Impact Subscore
Exploitability Subscore
4.7/10
6.9/10
3.4/10
Exploit range
Attack complexity
Authentication
Local
Medium
No required
Confidentiality impact
Integrity impact
Availability impact
None
None
Complete

Hello,

Linux kernel built with the IPv6 protocol(CONFIG_IPv6) along with the IPv6 source address based routing
support(CONFIG_IPV6_SUBTREE) is vulnerable to a NULL pointer dereference flaw. It could occur while doing an
ioctl(SIOCADDRT) call on an IPv6 socket. User would need to have CAP_NET_ADMIN privileges to perform such a call.

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()").

A user/program with CAP_NET_ADMIN privileges could use this flaw to crash a
system resulting in DoS.

Upstream fix:
-------------
-> https://git.kernel.org/linus/ae7b4e1f213aa659aedf9c6ecad0bf5f0476e1e2


-rw-r--r-- net/ipv6/ip6_fib.c 2
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index 73db48e..5bec666 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -825,9 +825,9 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt, struct nl_info *info)
fn = fib6_add_1(root, &rt->rt6i_dst.addr, 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;
}


Reference:
----------
-> https://bugzilla.redhat.com/show_bug.cgi?id=1039054


Thank you.
--
Prasad J Pandit / Red Hat Security Response Team

References:

https://git.kernel.org/linus/ae7b4e1f213aa659aedf9c6ecad0bf5f0476e1e2
https://bugzilla.redhat.com/show_bug.cgi?id=1039054

See this note in TXT Version

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