Hi list,Since at least kernel 5.3.x (2019) and up to current 6.2.15, iptables -m string --algo bm does not work when added to the OUTPUT chain.
Quick reproducer (algo bm, does not work properly):
# iptables -I OUTPUT -p tcp -m string --algo bm --string 'GET /' -j DROP $ curl -s example.com | head -n3 ^^^^ curl executes successfully
This works (algo kmp, works properly):
# iptables -I OUTPUT -p tcp -m string --algo kmp --string 'GET /' -j DROP $ curl -s example.com | head -n ^^^^ curl does not execute successfully
See: https://bugzilla.netfilter.org/show_bug.cgi?id=1390
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