From nobody Fri Dec 19 20:13:04 2025 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.16]) (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 CFAA22741C0; Thu, 4 Dec 2025 09:09:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.16 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764839344; cv=none; b=lrLYB1lzHz1iCTl6cI0iG6t5uVeN1NDy3dkyPMfA/OJ2KSoqHXEh8vUyRjsIw5Af4w5HrSN7HChLJUc6BJt9DZ0xGRDoj74+qy1dTeCHvEPJIpHSlxvOX5tK8KpH+UXfAzzY/rrjS8ogvD0SfcxMl8L6jaG9+bxrN6kgY9Y1fds= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764839344; c=relaxed/simple; bh=3uz+62j3aS0I7ayKubAXY/2DmW+bLoIWENB2nYvuvuk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BC4dNTwXY6qrdh3sq/uvsuku2JCJ8xONhAajGYLz71BwZBdL0eewf05KGKO/xNTJLjHjLGd82nqC0UaXdGXiEbdAdEFKGVvI0DC4fF6B9ujiw0ltGMchvO5VRur0p/3dSrZb4w6H0cQPSga0PFF26i6c4rDaxeodMvuSR1DAL1Y= 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=mjArpjyo; arc=none smtp.client-ip=198.175.65.16 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="mjArpjyo" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1764839342; x=1796375342; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=3uz+62j3aS0I7ayKubAXY/2DmW+bLoIWENB2nYvuvuk=; b=mjArpjyoT5/lxRgEjk5kZUYLpPBADcdraGfZb6B2qLTy0eb9u0Kq02R4 /8qtwKQwyn8QUUCKP9UGS4RrmudctC+wwNm4elbVJsqlwHR4Bv/BbkSBq jixC5LZICeb/jbaIjr+YWBI3/QdWv5Dse3YcobqnFQaVCWtPR4fLuRKUo HGQ7TxQvMwhXqwf/b5LmXXWxtAE7u2CbKsiBKWco/YOxjB7CzVH8f98QJ PxyQgPMjoVjuaQZnkdyn2oNcIlFDpaZePBmXNWcn1khAmtXSc1hqKyX+I ofxg+3rhQC39Lx/v2YqOe5Jo/AoX1pKkSxQeRIImOaqhsJ5f2NNBmhnAI A==; X-CSE-ConnectionGUID: QiWvQPqVTQ6B5MUnVN+Vqg== X-CSE-MsgGUID: WdUrFVQmTjafPjnc7k/2EQ== X-IronPort-AV: E=McAfee;i="6800,10657,11631"; a="67014017" X-IronPort-AV: E=Sophos;i="6.20,248,1758610800"; d="scan'208";a="67014017" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa108.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Dec 2025 01:09:01 -0800 X-CSE-ConnectionGUID: 7E9px2DcR92EG9AixfTn2Q== X-CSE-MsgGUID: y0EctHCqQXmU6w7PX/xsyA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.20,248,1758610800"; d="scan'208";a="195724274" Received: from junjie-nuc14rvs.bj.intel.com ([10.238.152.23]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Dec 2025 01:08:58 -0800 From: Junjie Cao To: pabeni@redhat.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, 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 1/2] netrom: fix possible deadlock in nr_rt_device_down Date: Thu, 4 Dec 2025 17:09:04 +0800 Message-ID: <20251204090905.28663-2-junjie.cao@intel.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251204090905.28663-1-junjie.cao@intel.com> References: <20251204090905.28663-1-junjie.cao@intel.com> 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, and a second one that removes unused neighbours under nr_neigh_list_lock. Also adjust nr_rt_free() to acquire nr_node_list_lock before nr_neigh_list_lock so that the global lock ordering remains consistent. [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 Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Junjie Cao --- net/netrom/nr_route.c | 65 ++++++++++++++++++++++--------------------- 1 file changed, 33 insertions(+), 32 deletions(-) diff --git a/net/netrom/nr_route.c b/net/netrom/nr_route.c index b94cb2ffbaf8..20aacfdfccd4 100644 --- a/net/netrom/nr_route.c +++ b/net/netrom/nr_route.c @@ -508,40 +508,41 @@ void nr_rt_device_down(struct net_device *dev) { struct nr_neigh *s; struct hlist_node *nodet, *node2t; - struct nr_node *t; + 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) { + 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); } @@ -962,23 +963,23 @@ const struct seq_operations nr_neigh_seqops =3D { void nr_rt_free(void) { struct nr_neigh *s =3D NULL; - struct nr_node *t =3D NULL; + 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); nr_node_unlock(t); } nr_neigh_for_each_safe(s, nodet, &nr_neigh_list) { - while(s->count) { + while (s->count) { s->count--; nr_neigh_put(s); } 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