[PATCH v2 0/1] selftests: net: fix file owner for broadcast_ether_dst test

[PATCH v2 0/1] selftests: net: fix file owner for broadcast_ether_dst test

[Ross Porter]

The broadcast_ether_dst test can spuriously fail due to file
permissions, depending on which flags tcpdump is compiled with: If
tcpdump is compiled with the `--with-user` flag then tcpdump will
step down to the provided user after opening the device. In this
case the test fails due to permission issues, as the output file
is owned by a different user.
Debian ships tcpdump with this flag enabled, so this bug
appears as part of our kernel testing.

To fix this, we can ensure tcpdump remains as root (regardless of
whether it was compiled with `--with-user`) by passing the `-Z root`
argument when invoking it.

Changes in v2:
* Moved '-Z root' before filter expression for POSIX compliance

Link to v1:
https://lore.kernel.org/all/20260610062230.71573-1-ross.porter@canonical.com/

Ross Porter (1):
  selftests: net: fix file owner for broadcast_ether_dst test

 tools/testing/selftests/net/broadcast_ether_dst.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.53.0

[PATCH v2 1/1] selftests: net: fix file owner for broadcast_ether_dst test

[Ross Porter]

Ensure the output file is always owned by root (even if tcpdump was 
compiled with `--with-user`), by passing the `-Z root` argument when 
invoking it.

Cc: stable@vger.kernel.org
Reported-by: Edoardo Canepa <edoardo.canepa@canonical.com>
Closes: https://bugs.launchpad.net/ubuntu-kernel-tests/+bug/2129815
Fixes: bf59028ea8d4 ("selftests: net: add test for destination in broadcast packets")
Suggested-by: Edoardo Canepa <edoardo.canepa@canonical.com>
Tested-by: Ross Porter <ross.porter@canonical.com>
Signed-off-by: Ross Porter <ross.porter@canonical.com>
---
 tools/testing/selftests/net/broadcast_ether_dst.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/net/broadcast_ether_dst.sh b/tools/testing/selftests/net/broadcast_ether_dst.sh
index 334a7eca8a80..5e7a8fe23c7a 100755
--- 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}" -Z root icmp &> "${OUTPUT}" &
 	pid=$!
 	slowwait 1 grep -qs "listening" "${OUTPUT}"
 
-- 
2.53.0

Re: [PATCH v2 0/1] selftests: net: fix file owner for broadcast_ether_dst test

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 17 Jun 2026 18:10:38 +1200 you wrote:
> The broadcast_ether_dst test can spuriously fail due to file
> permissions, depending on which flags tcpdump is compiled with: If
> tcpdump is compiled with the `--with-user` flag then tcpdump will
> step down to the provided user after opening the device. In this
> case the test fails due to permission issues, as the output file
> is owned by a different user.
> Debian ships tcpdump with this flag enabled, so this bug
> appears as part of our kernel testing.
> 
> [...]

Here is the summary with links:
  - [v2,1/1] selftests: net: fix file owner for broadcast_ether_dst test
    https://git.kernel.org/netdev/net/c/b8613e979200

You are awesome, thank you!
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