Unix domain sockets missing error codes

[Adeel Sharif]

Hello,

We are a group of people working on making Linux safe for everyone. In
hope of doing that I started testing the system caalls. The one I am
currently working on is send/write.

If send() is used to send datagrams on unix socket and the receiver
has stopped receiving, but still connected, there is a high
possibility that Linux kernel could eat up the whole system memory.
Although there is a system wide limit on write memory from wmem_max
parameter but this is sometimes also increased to system memory size
in order to avoid packet drops.

After having a look in the kernel implementation of
unix_dgram_sendmsg() it is obvious that user buffers are copied into
kernel socket buffers and they are queued to a linked list. This list
is growing without any limits. Although there is a qlen parameter but
it is never used to impose a limit on it. Could we perhaps impose a
limit on it and return an error with errcode EQUEUE_FULL or something
instead?

I don't know who is the maintainer of unix sockets. If someone knows
please let me know and I will discuss with him further.

Thank You.