From nobody Mon Dec 1 22:06:14 2025 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.20]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F167D2356A4; Thu, 27 Nov 2025 08:41:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.20 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764232864; cv=none; b=DPYoldY9wfjfkaXL48W/mF7CZDekRF+T/CihX8ubgINA31mkzvfbzx6Naa5+cjzRAVsdLGU/RV2l6z7ILVGgKLtG2ULPkJHda7IBOrVAPDyZ9klJcxBajojxuyrI0tkfqVgFJI6NExfeQOYAeqS90ZiyP+Nw23pixvc7iY4JDzo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764232864; c=relaxed/simple; bh=jwpF5p7Btj34ZHiu4EGv+DefCVkf1TvTSypgzdIwT7E=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=rEUIJDivAGS/qugcTDIYvJmkrawiZqIggA4KZQSDyBl160OvCKEY2cKPlvpFDzM1LWSpbAL7lJiY1BFCN4v4wsyScXzitd1fCNF6yMVQYQdJbVK3QKBpBP/Dsmj+alsDDpt5BhL2qdJvGgakj3aa5WvF1tQwuu0t3PagJ+S/rOI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=SdI6h346; arc=none smtp.client-ip=198.175.65.20 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="SdI6h346" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1764232863; x=1795768863; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=jwpF5p7Btj34ZHiu4EGv+DefCVkf1TvTSypgzdIwT7E=; b=SdI6h346857Q6KTEFgxSBq6LbxznyT33v9WkTvXtOchwZj635aPG3iRl 8G1DSNEFNnl2V8RX0lI0poXJidM9AteBaaFO3d0J517ijcLRpZby7z4sA D2CGUhFBrTkiqx65N16ilM445k5Xa5qfp/hu+iP1KZRdDIeW6pfNLGQsk UEeQD9TH/WwnyFmOB9uK+bg0Ta42xeMjCf+ZkpekMC0/tKgEIS4gbC0/S 3uDPHEr1kN5Qaxg8RVV1+SlQ1qd8wMSFyPU3oaKSIioJmTPUkOFf5m75c uC7gSXUcE5rYcEtnb6yUvGDt/ZLBgnY5iEIj9O1E69BCWdi15r7waXTaF Q==; X-CSE-ConnectionGUID: /klX917wRBG3hkL6563k0w== X-CSE-MsgGUID: h5UpO9A5QZ2xspsX9NB1gQ== X-IronPort-AV: E=McAfee;i="6800,10657,11625"; a="65988441" X-IronPort-AV: E=Sophos;i="6.20,230,1758610800"; d="scan'208";a="65988441" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by orvoesa112.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Nov 2025 00:41:02 -0800 X-CSE-ConnectionGUID: Nc8FAxgaTtuOrKnhIBW+MQ== X-CSE-MsgGUID: vWf86RVcSzmTNVlSS3CfYw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.20,230,1758610800"; d="scan'208";a="192305036" Received: from junjie-nuc14rvs.bj.intel.com ([10.238.152.23]) by orviesa006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Nov 2025 00:40:59 -0800 From: Junjie Cao To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, syzbot+14afda08dc3484d5db82@syzkaller.appspotmail.com Cc: horms@kernel.org, linux-hams@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, stable@vger.kernel.org, junjie.cao@intel.com Subject: [PATCH] netrom: fix possible deadlock between nr_rt_ioctl() and nr_rt_device_down() Date: Thu, 27 Nov 2025 16:41:12 +0800 Message-ID: <20251127084112.123837-1-junjie.cao@intel.com> X-Mailer: git-send-email 2.43.0 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" syzbot reported a circular locking dependency involving nr_neigh_list_lock, nr_node_list_lock and nr_node->node_lock in the NET/ROM routing code [1]. One of the problematic scenarios looks like this: CPU0 CPU1 ---- ---- nr_rt_device_down() nr_rt_ioctl() lock(nr_neigh_list_lock); nr_del_node() ... lock(nr_node_list_lock); lock(nr_node_list_lock); nr_remove_neigh(); lock(nr_neigh_list_lock); This creates the following lock chain: nr_neigh_list_lock -> nr_node_list_lock -> &nr_node->node_lock while the ioctl path may acquire the locks in the opposite order via nr_dec_obs()/nr_del_node(), which makes lockdep complain about a possible deadlock. Refactor nr_rt_device_down() to avoid nested locking of nr_neigh_list_lock and nr_node_list_lock. The function now performs two separate passes: one that walks all nodes under nr_node_list_lock and drops routes / reference counts, and a second one that removes unused neighbours under nr_neigh_list_lock. This also fixes a reference count leak of nr_neigh in the node route removal path. [1] https://syzkaller.appspot.com/bug?extid=3D14afda08dc3484d5db82 Reported-by: syzbot+14afda08dc3484d5db82@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D14afda08dc3484d5db82 Tested-by: syzbot+14afda08dc3484d5db82@syzkaller.appspotmail.com Cc: stable@vger.kernel.org Signed-off-by: Junjie Cao --- net/netrom/nr_route.c | 61 +++++++++++++++++++++++-------------------- 1 file changed, 32 insertions(+), 29 deletions(-) diff --git a/net/netrom/nr_route.c b/net/netrom/nr_route.c index b94cb2ffbaf8..cc8c47e1340a 100644 --- a/net/netrom/nr_route.c +++ b/net/netrom/nr_route.c @@ -511,37 +511,40 @@ void nr_rt_device_down(struct net_device *dev) struct nr_node *t; int i; =20 - spin_lock_bh(&nr_neigh_list_lock); - nr_neigh_for_each_safe(s, nodet, &nr_neigh_list) { - if (s->dev =3D=3D dev) { - spin_lock_bh(&nr_node_list_lock); - nr_node_for_each_safe(t, node2t, &nr_node_list) { - nr_node_lock(t); - for (i =3D 0; i < t->count; i++) { - if (t->routes[i].neighbour =3D=3D s) { - t->count--; - - switch (i) { - case 0: - t->routes[0] =3D t->routes[1]; - fallthrough; - case 1: - t->routes[1] =3D t->routes[2]; - break; - case 2: - break; - } - } - } + spin_lock_bh(&nr_node_list_lock); + nr_node_for_each_safe(t, node2t, &nr_node_list) { + nr_node_lock(t); + for (i =3D 0; i < t->count; i++) { + s =3D t->routes[i].neighbour; + if (s->dev =3D=3D dev) { + s->count--; + nr_neigh_put(s); + t->count--; =20 - if (t->count <=3D 0) - nr_remove_node_locked(t); - nr_node_unlock(t); + switch (i) { + case 0: + t->routes[0] =3D t->routes[1]; + fallthrough; + case 1: + t->routes[1] =3D t->routes[2]; + break; + case 2: + break; + } + i--; } - spin_unlock_bh(&nr_node_list_lock); + } =20 + if (t->count <=3D 0) + nr_remove_node_locked(t); + nr_node_unlock(t); + } + spin_unlock_bh(&nr_node_list_lock); + + spin_lock_bh(&nr_neigh_list_lock); + nr_neigh_for_each_safe(s, nodet, &nr_neigh_list) { + if (s->dev =3D=3D dev) nr_remove_neigh_locked(s); - } } spin_unlock_bh(&nr_neigh_list_lock); } @@ -965,8 +968,8 @@ void nr_rt_free(void) struct nr_node *t =3D NULL; struct hlist_node *nodet; =20 - spin_lock_bh(&nr_neigh_list_lock); spin_lock_bh(&nr_node_list_lock); + spin_lock_bh(&nr_neigh_list_lock); nr_node_for_each_safe(t, nodet, &nr_node_list) { nr_node_lock(t); nr_remove_node_locked(t); @@ -979,6 +982,6 @@ void nr_rt_free(void) } nr_remove_neigh_locked(s); } - spin_unlock_bh(&nr_node_list_lock); spin_unlock_bh(&nr_neigh_list_lock); + spin_unlock_bh(&nr_node_list_lock); } --=20 2.43.0