Re: [PATCH v2] ipnetns: use-after-free problem in get_netnsid_from_name func

Re: [PATCH v2] ipnetns: use-after-free problem in get_netnsid_from_name func

[Zhiqiang Liu]

> Hi,
> 
> On Mon, Apr 29, 2019 at 03:38:39PM +0800, Zhiqiang Liu wrote:
>> From: Zhiqiang Liu <liuzhiqiang26@huawei.com>
>>
>> Follow the following steps:
>> # ip netns add net1
>> # export MALLOC_MMAP_THRESHOLD_=0
>> # ip netns list
>> then Segmentation fault (core dumped) will occur.
>>
>> In get_netnsid_from_name func, answer is freed before rta_getattr_u32(tb[NETNSA_NSID]),
>> where tb[] refers to answer`s content. If we set MALLOC_MMAP_THRESHOLD_=0, mmap will
>> be adoped to malloc memory, which will be freed immediately after calling free func.
>> So reading tb[NETNSA_NSID] will access the released memory after free(answer).
>>
>> Here, we will call get_netnsid_from_name(tb[NETNSA_NSID]) before free(answer).
>>
>> Fixes: 86bf43c7c2f ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
>> Reported-by: Huiying Kou <kouhuiying@huawei.com>
>> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> 
> Acked-by: Phil Sutter <phil@nwl.cc>
> 
> Please always Cc: netdev@vger.kernel.org for iproute2 patches.
> 
> Thanks, Phil

Thank you for reminding me. I will Cc: netdev@vger.kernel.org in the v3 patch.

> 
> .
> 

[PATCH iproute2 v3] ipnetns: use-after-free problem in get_netnsid_from_name func

[Zhiqiang Liu]

From: Zhiqiang Liu <liuzhiqiang26@huawei.com>

Follow the following steps:
# ip netns add net1
# export MALLOC_MMAP_THRESHOLD_=0
# ip netns list
then Segmentation fault (core dumped) will occur.

In get_netnsid_from_name func, answer is freed before rta_getattr_u32(tb[NETNSA_NSID]),
where tb[] refers to answer`s content. If we set MALLOC_MMAP_THRESHOLD_=0, mmap will
be adoped to malloc memory, which will be freed immediately after calling free func.
So reading tb[NETNSA_NSID] will access the released memory after free(answer).

Here, we will call get_netnsid_from_name(tb[NETNSA_NSID]) before free(answer).

Fixes: 86bf43c7c2f ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
Reported-by: Huiying Kou <kouhuiying@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Acked-by: Phil Sutter <phil@nwl.cc>
---
v2->v3: add Cc:netdev@vger.kernel.org suggested by Phil Sutter
v1->v2: correct commit log

 ip/ipnetns.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index 430d884..d72be95 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -107,7 +107,7 @@ int get_netnsid_from_name(const char *name)
 	struct nlmsghdr *answer;
 	struct rtattr *tb[NETNSA_MAX + 1];
 	struct rtgenmsg *rthdr;
-	int len, fd;
+	int len, fd, ret = -1;

 	netns_nsid_socket_init();

@@ -134,8 +134,9 @@ int get_netnsid_from_name(const char *name)
 	parse_rtattr(tb, NETNSA_MAX, NETNS_RTA(rthdr), len);

 	if (tb[NETNSA_NSID]) {
+		ret = rta_getattr_u32(tb[NETNSA_NSID]);
 		free(answer);
-		return rta_getattr_u32(tb[NETNSA_NSID]);
+		return ret;
 	}

 err_out:
-- 
1.8.3.1

Re: [PATCH iproute2 v3] ipnetns: use-after-free problem in get_netnsid_from_name func

[David Ahern]

On 5/4/19 1:26 AM, Zhiqiang Liu wrote:
>
> diff --git a/ip/ipnetns.c b/ip/ipnetns.c
> index 430d884..d72be95 100644
> --- a/ip/ipnetns.c
> +++ b/ip/ipnetns.c
> @@ -107,7 +107,7 @@ int get_netnsid_from_name(const char *name)
>  	struct nlmsghdr *answer;
>  	struct rtattr *tb[NETNSA_MAX + 1];
>  	struct rtgenmsg *rthdr;
> -	int len, fd;
> +	int len, fd, ret = -1;
> 
>  	netns_nsid_socket_init();
> 
> @@ -134,8 +134,9 @@ int get_netnsid_from_name(const char *name)
>  	parse_rtattr(tb, NETNSA_MAX, NETNS_RTA(rthdr), len);
> 
>  	if (tb[NETNSA_NSID]) {
> +		ret = rta_getattr_u32(tb[NETNSA_NSID]);
>  		free(answer);
> -		return rta_getattr_u32(tb[NETNSA_NSID]);
> +		return ret;

set ret here, drop the free, let it proceed down to the existing free
and return but now using ret. That way there is 1 exit path and handles
the cleanup.

>  	}
> 
>  err_out:
> 

Re: [PATCH iproute2 v3] ipnetns: use-after-free problem in get_netnsid_from_name func

[Zhiqiang Liu]

> On 5/4/19 1:26 AM, Zhiqiang Liu wrote:
>>
>> diff --git a/ip/ipnetns.c b/ip/ipnetns.c
>> index 430d884..d72be95 100644
>> --- a/ip/ipnetns.c
>> +++ b/ip/ipnetns.c
>> @@ -107,7 +107,7 @@ int get_netnsid_from_name(const char *name)
>>  	struct nlmsghdr *answer;
>>  	struct rtattr *tb[NETNSA_MAX + 1];
>>  	struct rtgenmsg *rthdr;
>> -	int len, fd;
>> +	int len, fd, ret = -1;
>>
>>  	netns_nsid_socket_init();
>>
>> @@ -134,8 +134,9 @@ int get_netnsid_from_name(const char *name)
>>  	parse_rtattr(tb, NETNSA_MAX, NETNS_RTA(rthdr), len);
>>
>>  	if (tb[NETNSA_NSID]) {
>> +		ret = rta_getattr_u32(tb[NETNSA_NSID]);
>>  		free(answer);
>> -		return rta_getattr_u32(tb[NETNSA_NSID]);
>> +		return ret;
> 
> set ret here, drop the free, let it proceed down to the existing free
> and return but now using ret. That way there is 1 exit path and handles
> the cleanup

Yes, you are right. I will do that in the v4 patch.
That is very nice of you. Thanks a lot.

[PATCH iproute2 v4] ipnetns: use-after-free problem in get_netnsid_from_name func

[Zhiqiang Liu]

From: Zhiqiang Liu <liuzhiqiang26@huawei.com>

Follow the following steps:
# ip netns add net1
# export MALLOC_MMAP_THRESHOLD_=0
# ip netns list
then Segmentation fault (core dumped) will occur.

In get_netnsid_from_name func, answer is freed before rta_getattr_u32(tb[NETNSA_NSID]),
where tb[] refers to answer`s content. If we set MALLOC_MMAP_THRESHOLD_=0, mmap will
be adoped to malloc memory, which will be freed immediately after calling free func.
So reading tb[NETNSA_NSID] will access the released memory after free(answer).

Here, we will call get_netnsid_from_name(tb[NETNSA_NSID]) before free(answer).

Fixes: 86bf43c7c2f ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
Reported-by: Huiying Kou <kouhuiying@huawei.com>
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Acked-by: Phil Sutter <phil@nwl.cc>
---
v3->v4: optimize code suggested by David Ahern
v2->v3: add Cc:netdev@vger.kernel.org suggested by Phil Sutter
v1->v2: correct commit log

 ip/ipnetns.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index 430d884..52aefac 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -107,7 +107,7 @@ int get_netnsid_from_name(const char *name)
 	struct nlmsghdr *answer;
 	struct rtattr *tb[NETNSA_MAX + 1];
 	struct rtgenmsg *rthdr;
-	int len, fd;
+	int len, fd, ret = -1;

 	netns_nsid_socket_init();

@@ -124,23 +124,22 @@ int get_netnsid_from_name(const char *name)

 	/* Validate message and parse attributes */
 	if (answer->nlmsg_type == NLMSG_ERROR)
-		goto err_out;
+		goto out;

 	rthdr = NLMSG_DATA(answer);
 	len = answer->nlmsg_len - NLMSG_SPACE(sizeof(*rthdr));
 	if (len < 0)
-		goto err_out;
+		goto out;

 	parse_rtattr(tb, NETNSA_MAX, NETNS_RTA(rthdr), len);

 	if (tb[NETNSA_NSID]) {
-		free(answer);
-		return rta_getattr_u32(tb[NETNSA_NSID]);
+		ret = rta_getattr_u32(tb[NETNSA_NSID]);
 	}

-err_out:
+out:
 	free(answer);
-	return -1;
+	return ret;
 }

 struct nsid_cache {
-- 
1.8.3.1

Re: [PATCH iproute2 v3] ipnetns: use-after-free problem in get_netnsid_from_name func

[Stephen Hemminger]

On Sat, 4 May 2019 15:26:25 +0800
Zhiqiang Liu <liuzhiqiang26@huawei.com> wrote:

> From: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> 
> Follow the following steps:
> # ip netns add net1
> # export MALLOC_MMAP_THRESHOLD_=0
> # ip netns list
> then Segmentation fault (core dumped) will occur.
> 
> In get_netnsid_from_name func, answer is freed before rta_getattr_u32(tb[NETNSA_NSID]),
> where tb[] refers to answer`s content. If we set MALLOC_MMAP_THRESHOLD_=0, mmap will
> be adoped to malloc memory, which will be freed immediately after calling free func.
> So reading tb[NETNSA_NSID] will access the released memory after free(answer).
> 
> Here, we will call get_netnsid_from_name(tb[NETNSA_NSID]) before free(answer).
> 
> Fixes: 86bf43c7c2f ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
> Reported-by: Huiying Kou <kouhuiying@huawei.com>
> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
> Acked-by: Phil Sutter <phil@nwl.cc>

Applied. You can get better and more detailed checks by running with
valgrind. Which is what I did after applying your patch.

Re: [PATCH iproute2 v3] ipnetns: use-after-free problem in get_netnsid_from_name func

[Zhiqiang Liu]

> On Sat, 4 May 2019 15:26:25 +0800
> Zhiqiang Liu <liuzhiqiang26@huawei.com> wrote:
> 
>> From: Zhiqiang Liu <liuzhiqiang26@huawei.com>
>>
>> Follow the following steps:
>> # ip netns add net1
>> # export MALLOC_MMAP_THRESHOLD_=0
>> # ip netns list
>> then Segmentation fault (core dumped) will occur.
>>
>> In get_netnsid_from_name func, answer is freed before rta_getattr_u32(tb[NETNSA_NSID]),
>> where tb[] refers to answer`s content. If we set MALLOC_MMAP_THRESHOLD_=0, mmap will
>> be adoped to malloc memory, which will be freed immediately after calling free func.
>> So reading tb[NETNSA_NSID] will access the released memory after free(answer).
>>
>> Here, we will call get_netnsid_from_name(tb[NETNSA_NSID]) before free(answer).
>>
>> Fixes: 86bf43c7c2f ("lib/libnetlink: update rtnl_talk to support malloc buff at run time")
>> Reported-by: Huiying Kou <kouhuiying@huawei.com>
>> Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
>> Acked-by: Phil Sutter <phil@nwl.cc>
> 
> Applied. You can get better and more detailed checks by running with
> valgrind. Which is what I did after applying your patch.

Thank you for your advice. I will learn how to use valgrind, and use it to
obtain more detailed checks.

> 
> .
>