From: Ido Schimmel <idosch@nvidia.com>
To: Mehul Rao <mehulrao@gmail.com>
Cc: dsahern@kernel.org, davem@davemloft.net, edumazet@google.com,
kuba@kernel.org, pabeni@redhat.com, horms@kernel.org,
petrm@nvidia.com, netdev@vger.kernel.org, stable@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: nexthop: fix percpu use-after-free in remove_nh_grp_entry
Date: Sun, 8 Mar 2026 12:00:20 +0200 [thread overview]
Message-ID: <20260308100020.GA1582491@shredder> (raw)
In-Reply-To: <20260306233821.196789-1-mehulrao@gmail.com>
On Fri, Mar 06, 2026 at 06:38:20PM -0500, Mehul Rao wrote:
> When removing a nexthop from a group, remove_nh_grp_entry() publishes
> the new group via rcu_assign_pointer() then immediately frees the
> removed entry's percpu stats with free_percpu(). However, the
> synchronize_net() grace period in the caller remove_nexthop_from_groups()
> runs after the free. RCU readers that entered before the publish still
> see the old group and can dereference the freed stats via
> nh_grp_entry_stats_inc() -> get_cpu_ptr(nhge->stats), causing a
> use-after-free on percpu memory.
>
> Fix by deferring the free_percpu() until after synchronize_net() in the
> caller. Removed entries are chained via nh_list onto a local deferred
> free list. After the grace period completes and all RCU readers have
> finished, the percpu stats are safely freed.
>
> Fixes: f4676ea74b85 ("net: nexthop: Add nexthop group entry stats")
> Cc: stable@vger.kernel.org
> Signed-off-by: Mehul Rao <mehulrao@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Do you have a reproducer? I would like to understand why we don't see it
in the torture tests (e.g., ipv4_torture) in fib_nexthops.sh.
next prev parent reply other threads:[~2026-03-08 10:00 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-06 23:38 [PATCH net] net: nexthop: fix percpu use-after-free in remove_nh_grp_entry Mehul Rao
2026-03-07 3:30 ` Eric Dumazet
2026-03-08 10:00 ` Ido Schimmel [this message]
2026-03-10 2:00 ` patchwork-bot+netdevbpf
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260308100020.GA1582491@shredder \
--to=idosch@nvidia.com \
--cc=davem@davemloft.net \
--cc=dsahern@kernel.org \
--cc=edumazet@google.com \
--cc=horms@kernel.org \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mehulrao@gmail.com \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=petrm@nvidia.com \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox