Re: [PATCH 27/38] sctp: Copy struct sctp_sock.autoclose to userspace using put_user()

[Kees Cook]

On Thu, Jan 18, 2018 at 1:31 PM, Laura Abbott  wrote:
> On 01/10/2018 06:02 PM, Kees Cook wrote:
>>
>> From: David Windsor 
>>
>> The autoclose field can be copied with put_user(), so there is no need to
>> use copy_to_user(). In both cases, hardened usercopy is being bypassed
>> since the size is constant, and not open to runtime manipulation.
>>
>> This patch is verbatim from Brad Spengler/PaX Team's PAX_USERCOPY
>> whitelisting code in the last public patch of grsecurity/PaX based on my
>> understanding of the code. Changes or omissions from the original code are
>> mine and don't reflect the original grsecurity/PaX code.
>>
>
> Just tried a quick rebase and it looks like this conflicts with
> c76f97c99ae6 ("sctp: make use of pre-calculated len")
> I don't think we can use put_user if we're copying via the full
> len?

It should be fine, since:

len = sizeof(int);

c76f97c99ae6 just does a swap of sizeof(int) with len, put_user() will
work in either case, since autoclose will always be int sized.

-Kees

>
> Thanks,
> Laura
>
>
>> Signed-off-by: David Windsor 
>> [kees: adjust commit log]
>> Cc: Vlad Yasevich 
>> Cc: Neil Horman 
>> Cc: "David S. Miller" 
>> Cc: linux-s...@vger.kernel.org
>> Cc: netdev@vger.kernel.org
>> Signed-off-by: Kees Cook 
>> ---
>>   net/sctp/socket.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
>> index efbc8f52c531..15491491ec88 100644
>> --- a/net/sctp/socket.c
>> +++ b/net/sctp/socket.c
>> @@ -5011,7 +5011,7 @@ static int sctp_getsockopt_autoclose(struct sock
>> *sk, int len, char __user *optv
>> len = sizeof(int);
>> if (put_user(len, optlen))
>> return -EFAULT;
>> -   if (copy_to_user(optval, _sk(sk)->autoclose, sizeof(int)))
>> +   if (put_user(sctp_sk(sk)->autoclose, (int __user *)optval))
>> return -EFAULT;
>> return 0;
>>   }
>>
>



-- 
Kees Cook
Pixel Security

Re: [PATCH 27/38] sctp: Copy struct sctp_sock.autoclose to userspace using put_user()

[Laura Abbott]

On 01/10/2018 06:02 PM, Kees Cook wrote:

From: David Windsor 

The autoclose field can be copied with put_user(), so there is no need to
use copy_to_user(). In both cases, hardened usercopy is being bypassed
since the size is constant, and not open to runtime manipulation.

This patch is verbatim from Brad Spengler/PaX Team's PAX_USERCOPY
whitelisting code in the last public patch of grsecurity/PaX based on my
understanding of the code. Changes or omissions from the original code are
mine and don't reflect the original grsecurity/PaX code.



Just tried a quick rebase and it looks like this conflicts with
c76f97c99ae6 ("sctp: make use of pre-calculated len")
I don't think we can use put_user if we're copying via the full
len?

Thanks,
Laura


Signed-off-by: David Windsor 
[kees: adjust commit log]
Cc: Vlad Yasevich 
Cc: Neil Horman 
Cc: "David S. Miller" 
Cc: linux-s...@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook 
---
  net/sctp/socket.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index efbc8f52c531..15491491ec88 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -5011,7 +5011,7 @@ static int sctp_getsockopt_autoclose(struct sock *sk, int 
len, char __user *optv
len = sizeof(int);
if (put_user(len, optlen))
return -EFAULT;
-   if (copy_to_user(optval, _sk(sk)->autoclose, sizeof(int)))
+   if (put_user(sctp_sk(sk)->autoclose, (int __user *)optval))
return -EFAULT;
return 0;
  }

[PATCH 27/38] sctp: Copy struct sctp_sock.autoclose to userspace using put_user()

[Kees Cook]

From: David Windsor 

The autoclose field can be copied with put_user(), so there is no need to
use copy_to_user(). In both cases, hardened usercopy is being bypassed
since the size is constant, and not open to runtime manipulation.

This patch is verbatim from Brad Spengler/PaX Team's PAX_USERCOPY
whitelisting code in the last public patch of grsecurity/PaX based on my
understanding of the code. Changes or omissions from the original code are
mine and don't reflect the original grsecurity/PaX code.

Signed-off-by: David Windsor 
[kees: adjust commit log]
Cc: Vlad Yasevich 
Cc: Neil Horman 
Cc: "David S. Miller" 
Cc: linux-s...@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kees Cook 
---
 net/sctp/socket.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index efbc8f52c531..15491491ec88 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -5011,7 +5011,7 @@ static int sctp_getsockopt_autoclose(struct sock *sk, int 
len, char __user *optv
len = sizeof(int);
if (put_user(len, optlen))
return -EFAULT;
-   if (copy_to_user(optval, _sk(sk)->autoclose, sizeof(int)))
+   if (put_user(sctp_sk(sk)->autoclose, (int __user *)optval))
return -EFAULT;
return 0;
 }
-- 
2.7.4