Bug 7420

Hi,

I was trying to increase the maximum socket buffer size (SB_MAX or kern.maxsockbuf)
in my kernel and I realized that the maximum I could go was: 2097151 (2^21 - 1).
If the SB_MAX was >= 2^21 I could not open any socket.

After spending a lot of time I realised that in the file:

kern/uipc_socket2.c in the sbreserve function there is the following line:

if (cc > sb_max * MCLBYTES / (MSIZE + MCLBYTES))

Taking into account that the highest number we can have is 2^32 -1 and that

MCLBYTES = 2048 = 2^11 it is obvious that if sb_max was 2^21 we would have
an overflow (sb_max * MCLBYTES = 2^21 * 2^11 = 2^32 overflow)

Fix: 

The above can be easily corrected by replacing the above line with the 
following:

if (cc > (sb_max / (MSIZE + MCLBYTES)) * MCLBYTES)

In this case we can have SB_MAX with greater values.

Thanks.