When replacing an existing sample action, if TCA_SAMPLE_TRUNC_SIZE is not
passed in the netlink request, s->truncate and s->trunc_size retain their
previous values from the prior configuration.

As a result, a user cannot disable packet truncation when replacing a
sample action unless the action is fully deleted and recreated. In
addition, the hardware offload state and netlink dump continue to report
truncation as active.

Fix this by explicitly resetting s->truncate to false and s->trunc_size
to 0 when TCA_SAMPLE_TRUNC_SIZE is omitted during tcf_sample_init().

Fixes: 5c56784d852a ("net/sched: act_sample: add support for packet truncation")
Signed-off-by: Khawar Ahemad <ahemadkhawar123@gmail.com>
---
 net/sched/act_sample.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/act_sample.c b/net/sched/act_sample.c
index 2ceb4d141b..2bdc7a0eb6 100644
--- a/net/sched/act_sample.c
+++ b/net/sched/act_sample.c
@@ -116,6 +116,9 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,
 	if (tb[TCA_SAMPLE_TRUNC_SIZE]) {
 		s->truncate = true;
 		s->trunc_size = nla_get_u32(tb[TCA_SAMPLE_TRUNC_SIZE]);
+	} else {
+		s->truncate = false;
+		s->trunc_size = 0;
 	}
 	spin_unlock_bh(&s->tcf_lock);
 
-- 
2.54.0 (Apple Git-157)

On 8/25/26 6:01 PM, Khawar Ahemad wrote:
> When replacing an existing sample action, if TCA_SAMPLE_TRUNC_SIZE is not
> passed in the netlink request, s->truncate and s->trunc_size retain their
> previous values from the prior configuration.
> 
> As a result, a user cannot disable packet truncation when replacing a
> sample action unless the action is fully deleted and recreated. In
> addition, the hardware offload state and netlink dump continue to report
> truncation as active.
> 
> Fix this by explicitly resetting s->truncate to false and s->trunc_size
> to 0 when TCA_SAMPLE_TRUNC_SIZE is omitted during tcf_sample_init().
> 
> Fixes: 5c56784d852a ("net/sched: act_sample: add support for packet truncation")
> Signed-off-by: Khawar Ahemad <ahemadkhawar123@gmail.com>
## Form letter - net-next-closed

net-next pull request for v7.3 has already been merged, and therefore
the net-next tree is closed for new drivers, features, code refactoring
and optimizations. We are currently accepting bug fixes only.

Please repost when net-next reopens after Aug 31st.

RFC patches sent for review only are obviously welcome at any time.

See:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html#development-cycle
-- 
pw-bot: defer
pv-bot: closed

On 25/08/2026 13:01, Khawar Ahemad wrote:
> When replacing an existing sample action, if TCA_SAMPLE_TRUNC_SIZE is not
> passed in the netlink request, s->truncate and s->trunc_size retain their
> previous values from the prior configuration.
> 
> As a result, a user cannot disable packet truncation when replacing a
> sample action unless the action is fully deleted and recreated. In
> addition, the hardware offload state and netlink dump continue to report
> truncation as active.
> 
> Fix this by explicitly resetting s->truncate to false and s->trunc_size
> to 0 when TCA_SAMPLE_TRUNC_SIZE is omitted during tcf_sample_init().

This would be a behavioural regression. Users are not expecting that
a replace omitting truncation parameters will silently overwrite their
previous truncation settings. Can you instead create a new netlink
attribute? Something like "TCA_SAMPLE_FLAGS" which might have a
flag telling the action to unset this parameter?
Other option is to interpret 0 as "unset", but that might break
some setups.
Your fixes commit doesn't seem to exist and, since this is a fix,
you should target net and not net-next.
Also remember to wait 24 hours before posting a v2.

cheers,
Victor