[PATCH 1/1] NET: ipv6, fix potential null dereference

[PATCH 1/1] NET: ipv6, fix potential null dereference

[Jiri Slaby]

Stanse found a potential null dereference in snmp6_unregister_dev.
There is a check for idev being NULL, but it is dereferenced
earlier. Move the dereference after the check.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: "Pekka Savola (ipv6)" <pekkas@netcore.fi>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Cc: netdev@vger.kernel.org
---
 net/ipv6/proc.c |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
index c9605c3..53f4ef5 100644
--- a/net/ipv6/proc.c
+++ b/net/ipv6/proc.c
@@ -256,11 +256,12 @@ int snmp6_register_dev(struct inet6_dev *idev)
 
 int snmp6_unregister_dev(struct inet6_dev *idev)
 {
-	struct net *net = dev_net(idev->dev);
-	if (!net->mib.proc_net_devsnmp6)
-		return -ENOENT;
+	struct net *net;
 	if (!idev || !idev->stats.proc_dir_entry)
 		return -EINVAL;
+	net = dev_net(idev->dev);
+	if (!net->mib.proc_net_devsnmp6)
+		return -ENOENT;
 	remove_proc_entry(idev->stats.proc_dir_entry->name,
 			  net->mib.proc_net_devsnmp6);
 	idev->stats.proc_dir_entry = NULL;
-- 
1.6.5.7

Re: [PATCH 1/1] NET: ipv6, fix potential null dereference

[Alexey Dobriyan]

> Stanse found a potential null dereference

Nobody learns from Coverity, it seems. :^)

snmp6_unregister_dev() always called with valid idev.

Re: [PATCH 1/1] NET: ipv6, fix potential null dereference

[Jiri Slaby]

On 01/10/2010 11:35 AM, Alexey Dobriyan wrote:
>> Stanse found a potential null dereference
> 
> Nobody learns from Coverity, it seems. :^)

If it is known, why the test is still there?

I don't have access to the Coverity results anyway.

> snmp6_unregister_dev() always called with valid idev.

Ok, I'll post a patch to remove the check.

thanks,
-- 
js

[PATCH 1/1] NET: ipv6, remove unnecessary check

[Jiri Slaby]

Stanse found a potential null dereference in snmp6_unregister_dev.
There is a check for idev being NULL, but it is dereferenced
earlier. But idev cannot be NULL when passed to
snmp6_unregister_dev, so remove the test.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: "Pekka Savola (ipv6)" <pekkas@netcore.fi>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Cc: netdev@vger.kernel.org
---
 net/ipv6/proc.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
index c9605c3..7b197b7 100644
--- a/net/ipv6/proc.c
+++ b/net/ipv6/proc.c
@@ -259,7 +259,7 @@ int snmp6_unregister_dev(struct inet6_dev *idev)
 	struct net *net = dev_net(idev->dev);
 	if (!net->mib.proc_net_devsnmp6)
 		return -ENOENT;
-	if (!idev || !idev->stats.proc_dir_entry)
+	if (!idev->stats.proc_dir_entry)
 		return -EINVAL;
 	remove_proc_entry(idev->stats.proc_dir_entry->name,
 			  net->mib.proc_net_devsnmp6);
-- 
1.6.5.7

Re: [PATCH 1/1] NET: ipv6, fix potential null dereference

[Alexey Dobriyan]

On Sun, Jan 10, 2010 at 11:38:57AM +0100, Jiri Slaby wrote:
> On 01/10/2010 11:35 AM, Alexey Dobriyan wrote:
> >> Stanse found a potential null dereference
> > 
> > Nobody learns from Coverity, it seems. :^)
> 
> If it is known, why the test is still there?
> 
> I don't have access to the Coverity results anyway.

Well, when Coverity first exposed their database there were innumerable
"potential NULL dereference" defects and people fixed them by moving
stuff and most were bogus and there were flamewars and there were second
wave and so on...

Apparently "check all callers" is very hard to do programmatically.

> > snmp6_unregister_dev() always called with valid idev.

irda patch is not right too: calling tty->ops->hook with NULL tty is
impossible.

Re: [PATCH 1/1] NET: ipv6, fix potential null dereference

[Jiri Slaby]

On 01/10/2010 11:47 AM, Alexey Dobriyan wrote:
> On Sun, Jan 10, 2010 at 11:38:57AM +0100, Jiri Slaby wrote:
>> On 01/10/2010 11:35 AM, Alexey Dobriyan wrote:
>>>> Stanse found a potential null dereference
>>>
>>> Nobody learns from Coverity, it seems. :^)
>>
>> If it is known, why the test is still there?
>>
>> I don't have access to the Coverity results anyway.
> 
> Well, when Coverity first exposed their database there were innumerable
> "potential NULL dereference" defects and people fixed them by moving
> stuff and most were bogus and there were flamewars and there were second
> wave and so on...

Well, it is a clear error. Either the check is superfluous, or there is
a potential NULL dereference.

And until people start to look at the reports for their stuff
themselves, they will get bogus fixes from others. And they have to nack
them, indeed.

While we are at it, could anybody look at (watch `task'):
int xprt_reserve_xprt(struct rpc_task *task)
{
        struct rpc_rqst *req = task->tk_rqstp; <---- here
        struct rpc_xprt *xprt = req->rq_xprt;

        if (test_and_set_bit(XPRT_LOCKED, &xprt->state)) {
                if (task == xprt->snd_task)
                        return 1;
                if (task == NULL)  <------- here
                        return 0;

And this (I checked 2.6.28, where netdev_priv was dev->priv):
static void __devexit de_remove_one (struct pci_dev *pdev)
{
        struct net_device *dev = pci_get_drvdata(pdev);
        struct de_private *de = netdev_priv(dev);

        BUG_ON(!dev);

I know, currently netdev_priv returns dev+offset, but will this hold in
the future?

>>> snmp6_unregister_dev() always called with valid idev.
> 
> irda patch is not right too: calling tty->ops->hook with NULL tty is
> impossible.

Yup, I somehow messed with tty->driver_data being NULL.

thanks,
-- 
js

Re: [PATCH 1/1] NET: ipv6, fix potential null dereference

[Jiri Slaby]

On 01/10/2010 12:05 PM, Jiri Slaby wrote:
> And until people start to look at the reports for their stuff
> themselves, they will get bogus fixes from others. And they have to nack
> them, indeed.

Plus people sending such patches should plug in their brain. The tty
case is clearly bogus.

Re: [PATCH 1/1] NET: ipv6, remove unnecessary check

[David Miller]

From: Jiri Slaby <jslaby@suse.cz>
Date: Sun, 10 Jan 2010 11:43:03 +0100

> Stanse found a potential null dereference in snmp6_unregister_dev.
> There is a check for idev being NULL, but it is dereferenced
> earlier. But idev cannot be NULL when passed to
> snmp6_unregister_dev, so remove the test.
> 
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>

Applied.