netstack/ipv4: drop TTL=1 packets instead of forwarding with TTL=0#13521
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netstack/ipv4: drop TTL=1 packets instead of forwarding with TTL=0#13521TristanInSec wants to merge 1 commit into
TristanInSec wants to merge 1 commit into
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The TTL check in forwardUnicastPacket uses ttl == 0, so packets arriving with TTL=1 pass the check, get decremented to TTL=0 in forwardPacketWithRoute, and are forwarded with a zero TTL. There is no post-decrement TTL check. Linux ip_forward() checks ip_hdr(skb)->ttl <= 1 before forwarding, which correctly drops TTL=1 packets and sends ICMP Time Exceeded. Change the pre-decrement check from ttl == 0 to ttl <= 1 so that packets that would reach zero after the mandatory decrement are dropped with an ICMP Time Exceeded response.
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The TTL check in forwardUnicastPacket uses
ttl == 0, so packets arriving with TTL=1 pass the check, get decremented to TTL=0 in forwardPacketWithRoute, and are forwarded with a zero TTL. There is no post-decrement TTL check.Linux
ip_forward()checksip_hdr(skb)->ttl <= 1before forwarding, which correctly drops TTL=1 packets and sends ICMP Time Exceeded.This changes the pre-decrement check from
ttl == 0tottl <= 1so that packets that would reach zero after the mandatory decrement are dropped with an ICMP Time Exceeded response.