Re: [PATCH 06/10] ipc: Don't allocate a copy larger than max

Re: [PATCH 06/10] ipc: Don't allocate a copy larger than max

[Manfred Spraul]

Hi Peter,

You wrote:
> When MSG_COPY is set, a duplicate message must be allocated for
> the copy before locking the queue. However, the copy could
> not be larger than was sent which is limited to msg_ctlmax.
>
> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
> ---
>   ipc/msg.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/ipc/msg.c b/ipc/msg.c
> index 950572f..31cd1bf 100644
> --- a/ipc/msg.c
> +++ b/ipc/msg.c
> @@ -820,15 +820,17 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
>   	struct msg_msg *copy = NULL;
>   	unsigned long copy_number = 0;
>   
> +	ns = current->nsproxy->ipc_ns;
> +
>   	if (msqid < 0 || (long) bufsz < 0)
>   		return -EINVAL;
>   	if (msgflg & MSG_COPY) {
> -		copy = prepare_copy(buf, bufsz, msgflg, &msgtyp, &copy_number);
> +		copy = prepare_copy(buf, min_t(size_t, bufsz, ns->msg_ctlmax),
> +				    msgflg, &msgtyp, &copy_number);

What about:
- increase msg_ctlmax
- send message
- reduce msg_ctlmax

The side effects of the patch are odd:
- without MSG_COPY, a message can be read regardsless of the size.
   The user could check for E2BIG and increase the buffer size until
   msgrcv succeeds.
- with MSG_COPY, something else would happen.
   As far as I can see, it would oops: msg_ctlmax bytes are allocated,
   then the E2BIG test is against bufsz, and copy_msg() doesn't check
   the size of the target buffer.

I.e.: I would propose to revert the patch.

--
	Manfred
  

Re: [PATCH 06/10] ipc: Don't allocate a copy larger than max

[Peter Hurley]

On 05/25/2013 08:04 AM, Manfred Spraul wrote:
> Hi Peter,
>
> You wrote:
>> When MSG_COPY is set, a duplicate message must be allocated for
>> the copy before locking the queue. However, the copy could
>> not be larger than was sent which is limited to msg_ctlmax.
>>
>> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
>> ---
>>   ipc/msg.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/ipc/msg.c b/ipc/msg.c
>> index 950572f..31cd1bf 100644
>> --- a/ipc/msg.c
>> +++ b/ipc/msg.c
>> @@ -820,15 +820,17 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
>>       struct msg_msg *copy = NULL;
>>       unsigned long copy_number = 0;
>> +    ns = current->nsproxy->ipc_ns;
>> +
>>       if (msqid < 0 || (long) bufsz < 0)
>>           return -EINVAL;
>>       if (msgflg & MSG_COPY) {
>> -        copy = prepare_copy(buf, bufsz, msgflg, &msgtyp, &copy_number);
>> +        copy = prepare_copy(buf, min_t(size_t, bufsz, ns->msg_ctlmax),
>> +                    msgflg, &msgtyp, &copy_number);
>
> What about:
> - increase msg_ctlmax
> - send message
> - reduce msg_ctlmax
>
> The side effects of the patch are odd:
> - without MSG_COPY, a message can be read regardsless of the size.
>    The user could check for E2BIG and increase the buffer size until
>    msgrcv succeeds.

The patch does not change the behavior of non-MSG_COPY msg receive.

> - with MSG_COPY, something else would happen.
>    As far as I can see, it would oops: msg_ctlmax bytes are allocated,
>    then the E2BIG test is against bufsz, and copy_msg() doesn't check
>    the size of the target buffer.

I assume you are using 3.9

Current mainline returns EINVAL.

Regards,
Peter Hurley

[PATCH 06/10] ipc: Don't allocate a copy larger than max

[Peter Hurley]

When MSG_COPY is set, a duplicate message must be allocated for
the copy before locking the queue. However, the copy could
not be larger than was sent which is limited to msg_ctlmax.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
 ipc/msg.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/ipc/msg.c b/ipc/msg.c
index 950572f..31cd1bf 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -820,15 +820,17 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp,
 	struct msg_msg *copy = NULL;
 	unsigned long copy_number = 0;
 
+	ns = current->nsproxy->ipc_ns;
+
 	if (msqid < 0 || (long) bufsz < 0)
 		return -EINVAL;
 	if (msgflg & MSG_COPY) {
-		copy = prepare_copy(buf, bufsz, msgflg, &msgtyp, &copy_number);
+		copy = prepare_copy(buf, min_t(size_t, bufsz, ns->msg_ctlmax),
+				    msgflg, &msgtyp, &copy_number);
 		if (IS_ERR(copy))
 			return PTR_ERR(copy);
 	}
 	mode = convert_mode(&msgtyp, msgflg);
-	ns = current->nsproxy->ipc_ns;
 
 	msq = msg_lock_check(ns, msqid);
 	if (IS_ERR(msq)) {
-- 
1.8.1.2