Re: [PATCH 1/1] selftests: net: fix file owner for broadcast_ether_dst test

[Jakub Kicinski <kuba@kernel.org>]

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---
selftests: net: fix file owner for broadcast_ether_dst test

This commit ensures the tcpdump output file in the broadcast_ether_dst test
is always owned by root by passing the -Z root argument.

> diff --git a/tools/testing/selftests/net/broadcast_ether_dst.sh b/tools/testing/selftests/net/broadcast_ether_dst.sh
> --- a/tools/testing/selftests/net/broadcast_ether_dst.sh
> +++ b/tools/testing/selftests/net/broadcast_ether_dst.sh
> @@ -44,7 +44,7 @@ test_broadcast_ether_dst() {
>  	# tcpdump will exit after receiving a single packet
>  	# timeout will kill tcpdump if it is still running after 2s
>  	timeout 2s ip netns exec "${CLIENT_NS}" \
> -		tcpdump -i link0 -c 1 -w "${CAPFILE}" icmp &> "${OUTPUT}" &
> +		tcpdump -i link0 -c 1 -w "${CAPFILE}" icmp -Z root &> "${OUTPUT}" &

[Severity: Medium]
Will this tcpdump command fail with a syntax error in test_broadcast_ether_dst()
on systems that use musl libc or when POSIXLY_CORRECT is set?

By placing the -Z root option after the positional filter expression icmp,
standard POSIX option parsing will stop at the first non-option argument.

While this works on glibc systems because getopt() permutes arguments by
default, on strict POSIX systems tcpdump might treat -Z root as part of the
filter expression. This would concatenate the arguments into "icmp -Z root"
and cause a fatal pcap filter compilation error, breaking the selftest
unconditionally in those environments.

Could the -Z root argument be moved before the icmp filter expression?
-- 
pw-bot: cr