file: /proc/sys/net/ipv4/conf/interface/accept_source_route
variable: net.ipv4.conf.interface.accept_source_route
Official reference

Accept packets with SRR option. conf/all/accept_source_route must also be set to TRUE to accept packets with SRR option on the interface default TRUE (router) FALSE (host)

Nb: per interface setting (where “interface” is the name of your network interface); “all” is a special interface: changes the settings for all interfaces.