https://github.com/torvalds/linux
Revision 84ad0af0bccd3691cb951c2974c5cb2c10594d4a authored by Peilin Ye on 11 June 2023, 03:30:25 UTC, committed by Paolo Abeni on 14 June 2023, 08:31:39 UTC
mini_Qdisc_pair::p_miniq is a double pointer to mini_Qdisc, initialized in ingress_init() to point to net_device::miniq_ingress. ingress Qdiscs access this per-net_device pointer in mini_qdisc_pair_swap(). Similar for clsact Qdiscs and miniq_egress. Unfortunately, after introducing RTNL-unlocked RTM_{NEW,DEL,GET}TFILTER requests (thanks Hillf Danton for the hint), when replacing ingress or clsact Qdiscs, for example, the old Qdisc ("@old") could access the same miniq_{in,e}gress pointer(s) concurrently with the new Qdisc ("@new"), causing race conditions [1] including a use-after-free bug in mini_qdisc_pair_swap() reported by syzbot: BUG: KASAN: slab-use-after-free in mini_qdisc_pair_swap+0x1c2/0x1f0 net/sched/sch_generic.c:1573 Write of size 8 at addr ffff888045b31308 by task syz-executor690/14901 ... Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106 print_address_description.constprop.0+0x2c/0x3c0 mm/kasan/report.c:319 print_report mm/kasan/report.c:430 [inline] kasan_report+0x11c/0x130 mm/kasan/report.c:536 mini_qdisc_pair_swap+0x1c2/0x1f0 net/sched/sch_generic.c:1573 tcf_chain_head_change_item net/sched/cls_api.c:495 [inline] tcf_chain0_head_change.isra.0+0xb9/0x120 net/sched/cls_api.c:509 tcf_chain_tp_insert net/sched/cls_api.c:1826 [inline] tcf_chain_tp_insert_unique net/sched/cls_api.c:1875 [inline] tc_new_tfilter+0x1de6/0x2290 net/sched/cls_api.c:2266 ... @old and @new should not affect each other. In other words, @old should never modify miniq_{in,e}gress after @new, and @new should not update @old's RCU state. Fixing without changing sch_api.c turned out to be difficult (please refer to Closes: for discussions). Instead, make sure @new's first call always happen after @old's last call (in {ingress,clsact}_destroy()) has finished: In qdisc_graft(), return -EBUSY if @old has any ongoing filter requests, and call qdisc_destroy() for @old before grafting @new. Introduce qdisc_refcount_dec_if_one() as the counterpart of qdisc_refcount_inc_nz() used for filter requests. Introduce a non-static version of qdisc_destroy() that does a TCQ_F_BUILTIN check, just like qdisc_put() etc. Depends on patch "net/sched: Refactor qdisc_graft() for ingress and clsact Qdiscs". [1] To illustrate, the syzkaller reproducer adds ingress Qdiscs under TC_H_ROOT (no longer possible after commit c7cfbd115001 ("net/sched: sch_ingress: Only create under TC_H_INGRESS")) on eth0 that has 8 transmission queues: Thread 1 creates ingress Qdisc A (containing mini Qdisc a1 and a2), then adds a flower filter X to A. Thread 2 creates another ingress Qdisc B (containing mini Qdisc b1 and b2) to replace A, then adds a flower filter Y to B. Thread 1 A's refcnt Thread 2 RTM_NEWQDISC (A, RTNL-locked) qdisc_create(A) 1 qdisc_graft(A) 9 RTM_NEWTFILTER (X, RTNL-unlocked) __tcf_qdisc_find(A) 10 tcf_chain0_head_change(A) mini_qdisc_pair_swap(A) (1st) | | RTM_NEWQDISC (B, RTNL-locked) RCU sync 2 qdisc_graft(B) | 1 notify_and_destroy(A) | tcf_block_release(A) 0 RTM_NEWTFILTER (Y, RTNL-unlocked) qdisc_destroy(A) tcf_chain0_head_change(B) tcf_chain0_head_change_cb_del(A) mini_qdisc_pair_swap(B) (2nd) mini_qdisc_pair_swap(A) (3rd) | ... ... Here, B calls mini_qdisc_pair_swap(), pointing eth0->miniq_ingress to its mini Qdisc, b1. Then, A calls mini_qdisc_pair_swap() again during ingress_destroy(), setting eth0->miniq_ingress to NULL, so ingress packets on eth0 will not find filter Y in sch_handle_ingress(). This is just one of the possible consequences of concurrently accessing miniq_{in,e}gress pointers. Fixes: 7a096d579e8e ("net: sched: ingress: set 'unlocked' flag for Qdisc ops") Fixes: 87f373921c4e ("net: sched: ingress: set 'unlocked' flag for clsact Qdisc ops") Reported-by: syzbot+b53a9c0d1ea4ad62da8b@syzkaller.appspotmail.com Closes: https://lore.kernel.org/r/0000000000006cf87705f79acf1a@google.com/ Cc: Hillf Danton <hdanton@sina.com> Cc: Vlad Buslov <vladbu@mellanox.com> Signed-off-by: Peilin Ye <peilin.ye@bytedance.com> Acked-by: Jamal Hadi Salim <jhs@mojatatu.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
1 parent 2d5f6a8
Tip revision: 84ad0af0bccd3691cb951c2974c5cb2c10594d4a authored by Peilin Ye on 11 June 2023, 03:30:25 UTC
net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting
net/sched: qdisc_destroy() old ingress and clsact Qdiscs before grafting
Tip revision: 84ad0af
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