This is a note to let you know that I've just added the patch titled net: sched: disallow noqueue for qdisc classes to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-sched-disallow-noqueue-for-qdisc-classes.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 96398560f26aa07e8f2969d73c8197e6a6d10407 Mon Sep 17 00:00:00 2001 From: Frederick Lawler <fred@xxxxxxxxxxxxxx> Date: Mon, 9 Jan 2023 10:39:06 -0600 Subject: net: sched: disallow noqueue for qdisc classes From: Frederick Lawler <fred@xxxxxxxxxxxxxx> commit 96398560f26aa07e8f2969d73c8197e6a6d10407 upstream. While experimenting with applying noqueue to a classful queue discipline, we discovered a NULL pointer dereference in the __dev_queue_xmit() path that generates a kernel OOPS: # dev=enp0s5 # tc qdisc replace dev $dev root handle 1: htb default 1 # tc class add dev $dev parent 1: classid 1:1 htb rate 10mbit # tc qdisc add dev $dev parent 1:1 handle 10: noqueue # ping -I $dev -w 1 -c 1 1.1.1.1 [ 2.172856] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 2.173217] #PF: supervisor instruction fetch in kernel mode ... [ 2.178451] Call Trace: [ 2.178577] <TASK> [ 2.178686] htb_enqueue+0x1c8/0x370 [ 2.178880] dev_qdisc_enqueue+0x15/0x90 [ 2.179093] __dev_queue_xmit+0x798/0xd00 [ 2.179305] ? _raw_write_lock_bh+0xe/0x30 [ 2.179522] ? __local_bh_enable_ip+0x32/0x70 [ 2.179759] ? ___neigh_create+0x610/0x840 [ 2.179968] ? eth_header+0x21/0xc0 [ 2.180144] ip_finish_output2+0x15e/0x4f0 [ 2.180348] ? dst_output+0x30/0x30 [ 2.180525] ip_push_pending_frames+0x9d/0xb0 [ 2.180739] raw_sendmsg+0x601/0xcb0 [ 2.180916] ? _raw_spin_trylock+0xe/0x50 [ 2.181112] ? _raw_spin_unlock_irqrestore+0x16/0x30 [ 2.181354] ? get_page_from_freelist+0xcd6/0xdf0 [ 2.181594] ? sock_sendmsg+0x56/0x60 [ 2.181781] sock_sendmsg+0x56/0x60 [ 2.181958] __sys_sendto+0xf7/0x160 [ 2.182139] ? handle_mm_fault+0x6e/0x1d0 [ 2.182366] ? do_user_addr_fault+0x1e1/0x660 [ 2.182627] __x64_sys_sendto+0x1b/0x30 [ 2.182881] do_syscall_64+0x38/0x90 [ 2.183085] entry_SYSCALL_64_after_hwframe+0x63/0xcd ... [ 2.187402] </TASK> Previously in commit d66d6c3152e8 ("net: sched: register noqueue qdisc"), NULL was set for the noqueue discipline on noqueue init so that __dev_queue_xmit() falls through for the noqueue case. This also sets a bypass of the enqueue NULL check in the register_qdisc() function for the struct noqueue_disc_ops. Classful queue disciplines make it past the NULL check in __dev_queue_xmit() because the discipline is set to htb (in this case), and then in the call to __dev_xmit_skb(), it calls into htb_enqueue() which grabs a leaf node for a class and then calls qdisc_enqueue() by passing in a queue discipline which assumes ->enqueue() is not set to NULL. Fix this by not allowing classes to be assigned to the noqueue discipline. Linux TC Notes states that classes cannot be set to the noqueue discipline. [1] Let's enforce that here. Links: 1. https://linux-tc-notes.sourceforge.net/tc/doc/sch_noqueue.txt Fixes: d66d6c3152e8 ("net: sched: register noqueue qdisc") Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Frederick Lawler <fred@xxxxxxxxxxxxxx> Reviewed-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20230109163906.706000-1-fred@xxxxxxxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/sched/sch_api.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) --- a/net/sched/sch_api.c +++ b/net/sched/sch_api.c @@ -959,10 +959,14 @@ skip: if (cops && cops->graft) { unsigned long cl = cops->find(parent, classid); - if (cl) - err = cops->graft(parent, cl, new, &old); - else + if (cl) { + if (new && new->ops == &noqueue_qdisc_ops) + err = -EINVAL; + else + err = cops->graft(parent, cl, new, &old); + } else { err = -ENOENT; + } } if (!err) notify_and_destroy(net, skb, n, classid, old, new); Patches currently in stable-queue which might be from fred@xxxxxxxxxxxxxx are queue-4.14/net-sched-disallow-noqueue-for-qdisc-classes.patch