* Neil Horman:
On Thu, Jan 02, 2020 at 02:35:22PM +0100, Florian Weimer wrote:
> * Damian Ivanov:
> > I could not find any information if having the socket length limited
> > is still something that is required nowadays as it seems this is
> > mostly for compatibility reasons?
> I don't know why the kernel limits the socket length. There is no
> strict requirement to do so because the userspace interfaces all have
> explicit lengths. struct sockaddr_un has a fixed-size buffer, but
> that could be worked around, similar to struct dirent.
The kernel doesn't limit this length for any particular technical
reason, it limits it as a matter of maintaining ABI compatibility.
When the unix address family was written back in the 80's, they
decided that the sun_path component was coded to a length of 108
bytes, and so that is now part of the ABI, and can't be changed.
Any systemcall expecting a strict 108 byte path may encounter what
would appear to be an unterminated string, even if the only thing
you did was lengthen the path name.
The kernel would return an error in this case. It would be similar to
readlink with a buffer that is to small. The situation is actually
far more benign than with struct dirent, where the kernel happily
returns data that does not fit in the d_name array.