/etc/sysctl.d/99-gce.conf from Google Compute Engine source image ubuntu-1604-xenial-v20170811

99-gce.conf

# Requirements from Google. Documented at:
#       https://developers.google.com/compute/docs/images#buildingimage

# Prevent users from allocating low virtual memory
vm.mmap_min_addr = 65536

# enables syn flood protection
net.ipv4.tcp_syncookies = 1

# ignores source-routed packets
net.ipv4.conf.all.accept_source_route = 0

# ignores source-routed packets
net.ipv4.conf.default.accept_source_route = 0

# ignores ICMP redirects
net.ipv4.conf.all.accept_redirects = 0

# ignores ICMP redirects
net.ipv4.conf.default.accept_redirects = 0

# ignores ICMP redirects from non-GW hosts
net.ipv4.conf.all.secure_redirects = 1

# ignores ICMP redirects from non-GW hosts
net.ipv4.conf.default.secure_redirects = 1

# don't allow traffic between networks or act as a router
net.ipv4.ip_forward = 0

# don't allow traffic between networks or act as a router
net.ipv4.conf.all.send_redirects = 0

# don't allow traffic between networks or act as a router
net.ipv4.conf.default.send_redirects = 0

# reverse path filtering - IP spoofing protection
net.ipv4.conf.all.rp_filter = 1

# reverse path filtering - IP spoofing protection
net.ipv4.conf.default.rp_filter = 1

# reverse path filtering - IP spoofing protection
net.ipv4.conf.default.rp_filter = 1

# ignores ICMP broadcasts to avoid participating in Smurf attacks
net.ipv4.icmp_echo_ignore_broadcasts = 1

# ignores bad ICMP errors
net.ipv4.icmp_ignore_bogus_error_responses = 1

# logs spoofed, source-routed, and redirect packets
net.ipv4.conf.all.log_martians = 1

# log spoofed, source-routed, and redirect packets
net.ipv4.conf.default.log_martians = 1

# implements RFC 1337 fix
net.ipv4.tcp_rfc1337 = 1

# randomizes addresses of mmap base, heap, stack and VDSO page
kernel.randomize_va_space = 2

# provides protection from ToCToU races
fs.protected_hardlinks=1

# provides protection from ToCToU races
fs.protected_symlinks=1

# makes locating kernel addresses more difficult
kernel.kptr_restrict=1

# set ptrace protections
kernel.yama.ptrace_scope=1

# set perf only available to root
kernel.perf_event_paranoid=2