Bug 812551

Description of problem:

When client disconnects uncleanly, it might happen that an underlying
read() operation returns with an error.  This error was interpreted
wrongly because the negative return value was assigned to a variable
of unsigned type and being checked for <= 0. As this condition does
not hold in error case, a packet with wrong len (255) was sent instead
of aborting the client:

| read(0, 0x7fffa6dcfb12, 8) = -1 EIO (Input/output error)
| write(3, "\0\377\0\0\0\0\0\0\0\0", 10) = 10


The server accepts this broken packet and puts random data (stack
content) to the program:

| read(5, "\0\377\0\0\0\0\0\0\0\0", 10) = 10
| write(4, "\0\0\0\0\0\0\0\0\177~\377~\0\0\31\v|\352\377\177\0\0u\250C\335\347Hu\252\0E"..., 255) = 255


For reference, the 'pkt' is defined as

| struct packet
| {
| 	unsigned char type;
| 	unsigned char len;
| ...
| }


Version:

dtach-0.8-5.fc15.x86_64