Patchwork [net] net: fib: fib6_add: fix potential NULL pointer dereference

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Submitter Daniel Borkmann
Date Sept. 7, 2013, 1:13 p.m.
Message ID <1378559600-15858-1-git-send-email-dborkman@redhat.com>
Download mbox | patch
Permalink /patch/273382/
State Accepted
Delegated to: David Miller
Headers show

Comments

Daniel Borkmann - Sept. 7, 2013, 1:13 p.m.
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@redhat.com>
Cc: Lin Ming <mlin@ss.pku.edu.cn>
Cc: Matti Vaittinen <matti.vaittinen@nsn.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
---
 net/ipv6/ip6_fib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
Hannes Frederic Sowa - Sept. 7, 2013, 7:35 p.m.
On Sat, Sep 07, 2013 at 03:13:20PM +0200, Daniel Borkmann wrote:
> 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@redhat.com>
> Cc: Lin Ming <mlin@ss.pku.edu.cn>
> Cc: Matti Vaittinen <matti.vaittinen@nsn.com>
> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>

Full ACK!

Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>

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Matti Vaittinen - Sept. 9, 2013, 6:26 a.m.
On 09/07/2013 10:35 PM, ext Hannes Frederic Sowa wrote:
> On Sat, Sep 07, 2013 at 03:13:20PM +0200, Daniel Borkmann wrote:
>> 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@redhat.com>
>> Cc: Lin Ming <mlin@ss.pku.edu.cn>
>> Cc: Matti Vaittinen <matti.vaittinen@nsn.com>
>> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
>
> Full ACK!
>
> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
>
Acked-by: Matti Vaittinen <matti.vaittinen@nsn.com>
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David Miller - Sept. 11, 2013, 8:14 p.m.
From: Matti Vaittinen <matti.vaittinen@nsn.com>
Date: Mon, 09 Sep 2013 09:26:07 +0300

> On 09/07/2013 10:35 PM, ext Hannes Frederic Sowa wrote:
>> On Sat, Sep 07, 2013 at 03:13:20PM +0200, Daniel Borkmann wrote:
>>> 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@redhat.com>
>>> Cc: Lin Ming <mlin@ss.pku.edu.cn>
>>> Cc: Matti Vaittinen <matti.vaittinen@nsn.com>
>>> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
>>
>> Full ACK!
>>
>> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
>>
> Acked-by: Matti Vaittinen <matti.vaittinen@nsn.com>

Applied, thanks everyone.
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Patch

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;
 	}