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 <pe...@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
 


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