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[73.158.218.242]) by smtp.gmail.com with UTF8SMTPSA id d9443c01a7336-232044a0a23sm62082755ad.112.2025.05.20.13.20.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 May 2025 13:20:47 -0700 (PDT) From: Stanislav Fomichev To: netdev@vger.kernel.org Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, willemdebruijn.kernel@gmail.com, horms@kernel.org, stfomichev@gmail.com, linux-kernel@vger.kernel.org, syzbot+b191b5ccad8d7a986286@syzkaller.appspotmail.com Subject: [PATCH net] af_packet: move notifier's packet_dev_mc out of rcu critical section Date: Tue, 20 May 2025 13:20:46 -0700 Message-ID: <20250520202046.2620300-1-stfomichev@gmail.com> X-Mailer: git-send-email 2.49.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Calling `PACKET_ADD_MEMBERSHIP` on an ops-locked device can trigger the `NETDEV_UNREGISTER` notifier, which may require disabling promiscuous and/or allmulti mode. Both of these operations require acquiring the netdev instance lock. Move the call to `packet_dev_mc` outside of the RCU critical section. Closes: https://syzkaller.appspot.com/bug?extid=3Db191b5ccad8d7a986286 Reported-by: syzbot+b191b5ccad8d7a986286@syzkaller.appspotmail.com Fixes: ad7c7b2172c3 ("net: hold netdev instance lock during sysfs operation= s") Signed-off-by: Stanislav Fomichev --- net/packet/af_packet.c | 20 +++++++++++++++----- net/packet/internal.h | 1 + 2 files changed, 16 insertions(+), 5 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index d4dba06297c3..5a6132816b2e 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -3713,15 +3713,15 @@ static int packet_dev_mc(struct net_device *dev, st= ruct packet_mclist *i, } =20 static void packet_dev_mclist_delete(struct net_device *dev, - struct packet_mclist **mlp) + struct packet_mclist **mlp, + struct list_head *list) { struct packet_mclist *ml; =20 while ((ml =3D *mlp) !=3D NULL) { if (ml->ifindex =3D=3D dev->ifindex) { - packet_dev_mc(dev, ml, -1); + list_add(&ml->remove_list, list); *mlp =3D ml->next; - kfree(ml); } else mlp =3D &ml->next; } @@ -4233,9 +4233,11 @@ static int packet_getsockopt(struct socket *sock, in= t level, int optname, static int packet_notifier(struct notifier_block *this, unsigned long msg, void *ptr) { - struct sock *sk; struct net_device *dev =3D netdev_notifier_info_to_dev(ptr); struct net *net =3D dev_net(dev); + struct packet_mclist *ml, *tmp; + LIST_HEAD(mclist); + struct sock *sk; =20 rcu_read_lock(); sk_for_each_rcu(sk, &net->packet.sklist) { @@ -4244,7 +4246,8 @@ static int packet_notifier(struct notifier_block *thi= s, switch (msg) { case NETDEV_UNREGISTER: if (po->mclist) - packet_dev_mclist_delete(dev, &po->mclist); + packet_dev_mclist_delete(dev, &po->mclist, + &mclist); fallthrough; =20 case NETDEV_DOWN: @@ -4277,6 +4280,13 @@ static int packet_notifier(struct notifier_block *th= is, } } rcu_read_unlock(); + + /* packet_dev_mc might grab instance locks so can't run under rcu */ + list_for_each_entry_safe(ml, tmp, &mclist, remove_list) { + packet_dev_mc(dev, ml, -1); + kfree(ml); + } + return NOTIFY_DONE; } =20 diff --git a/net/packet/internal.h b/net/packet/internal.h index d5d70712007a..1e743d0316fd 100644 --- a/net/packet/internal.h +++ b/net/packet/internal.h @@ -11,6 +11,7 @@ struct packet_mclist { unsigned short type; unsigned short alen; unsigned char addr[MAX_ADDR_LEN]; + struct list_head remove_list; }; =20 /* kbdq - kernel block descriptor queue */ --=20 2.49.0