In the Linux kernel, the following vulnerability has been resolved:
net, sunrpc: Remap EPERM in case of connection failure in xstcpsetup_socket
When using a BPF program on kernelconnect(), the call can return -EPERM. This causes xstcpsetupsocket() to loop forever, filling up the syslog and causing the kernel to potentially freeze up.
Neil suggested:
This will propagate -EPERM up into other layers which might not be ready to handle it. It might be safer to map EPERM to an error we would be more likely to expect from the network system - such as ECONNREFUSED or ENETDOWN.
ECONNREFUSED as error seems reasonable. For programs setting a different error can be out of reach (see handling in 4fbac77d2d09) in particular on kernels which do not have f10d05966196 ("bpf: Make BPFPROGRUNARRAY return -err instead of allow boolean"), thus given that it is better to simply remap for consistent behavior. UDP does handle EPERM in xsudpsendrequest().