TIPC security issues

[Dan Rosenberg <drosenberg@vsecurity.com>]

The tipc_msg_build() function in net/tipc/msg.c is written in such a way
as to create a highly exploitable kernel heap overflow that would allow
a local user to escalate privileges to root by issuing maliciously
crafted sendmsg() calls.  At a minimum, the following issues should be
fixed:

1. The tipc_msg_calc_data_size() function is almost totally broken.  It
sums together size_t values (iov_lens), but returns an integer.  Two
things can go wrong - the total value can wrap around, or on 64-bit
platforms, iov_len values greater than UINT_MAX will be truncated.

2. The comparison of dsz to TIPC_MAX_USER_MSG_SIZE is signed, so
negative (large unsigned) values will pass this check.

3. The comparison of sz to max_size is also signed.

As a result of these issues, it's possible to cause the allocation of a
small heap buffer and the subsequent copying of a carefully controlled
larger amount of data into that buffer.

I haven't found a Linux distribution that defines a module alias for
TIPC (even though most compile it as a module), so an administrator will
have had to explicitly load the TIPC module for a system to be
vulnerable.

-Dan