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Message-ID: <CANn89iLeTqHYwdy=X8Lg+Pe23cJeX2B862Un5wB09=gzaGNG3w@mail.gmail.com>
Date: Mon, 7 Oct 2024 20:43:24 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
Cc: Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>,
Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org, eric.dumazet@...il.com,
syzbot <syzkaller@...glegroups.com>, Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net] net/sched: accept TCA_STAB only for root qdisc
On Mon, Oct 7, 2024 at 8:41 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Most qdiscs maintain their backlog using qdisc_pkt_len(skb)
> on the assumption it is invariant between the enqueue()
> and dequeue() handlers.
>
> Unfortunately syzbot can crash a host rather easily using
> a TBF + SFQ combination, with an STAB on SFQ [1]
>
> We can't support TCA_STAB on arbitrary level, this would
> require to maintain per-qdisc storage.
>
> [1]
> [ 88.796496] BUG: kernel NULL pointer dereference, address: 0000000000000000
> [ 88.798611] #PF: supervisor read access in kernel mode
> [ 88.799014] #PF: error_code(0x0000) - not-present page
> [ 88.799506] PGD 0 P4D 0
> [ 88.799829] Oops: Oops: 0000 [#1] SMP NOPTI
> [ 88.800569] CPU: 14 UID: 0 PID: 2053 Comm: b371744477 Not tainted 6.12.0-rc1-virtme #1117
> [ 88.801107] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> [ 88.801779] RIP: 0010:sfq_dequeue (net/sched/sch_sfq.c:272 net/sched/sch_sfq.c:499) sch_sfq
> [ 88.802544] Code: 0f b7 50 12 48 8d 04 d5 00 00 00 00 48 89 d6 48 29 d0 48 8b 91 c0 01 00 00 48 c1 e0 03 48 01 c2 66 83 7a 1a 00 7e c0 48 8b 3a <4c> 8b 07 4c 89 02 49 89 50 08 48 c7 47 08 00 00 00 00 48 c7 07 00
> All code
> ========
> 0: 0f b7 50 12 movzwl 0x12(%rax),%edx
> 4: 48 8d 04 d5 00 00 00 lea 0x0(,%rdx,8),%rax
> b: 00
> c: 48 89 d6 mov %rdx,%rsi
> f: 48 29 d0 sub %rdx,%rax
> 12: 48 8b 91 c0 01 00 00 mov 0x1c0(%rcx),%rdx
> 19: 48 c1 e0 03 shl $0x3,%rax
> 1d: 48 01 c2 add %rax,%rdx
> 20: 66 83 7a 1a 00 cmpw $0x0,0x1a(%rdx)
> 25: 7e c0 jle 0xffffffffffffffe7
> 27: 48 8b 3a mov (%rdx),%rdi
> 2a:* 4c 8b 07 mov (%rdi),%r8 <-- trapping instruction
> 2d: 4c 89 02 mov %r8,(%rdx)
> 30: 49 89 50 08 mov %rdx,0x8(%r8)
> 34: 48 c7 47 08 00 00 00 movq $0x0,0x8(%rdi)
> 3b: 00
> 3c: 48 rex.W
> 3d: c7 .byte 0xc7
> 3e: 07 (bad)
> ...
>
> Code starting with the faulting instruction
> ===========================================
> 0: 4c 8b 07 mov (%rdi),%r8
> 3: 4c 89 02 mov %r8,(%rdx)
> 6: 49 89 50 08 mov %rdx,0x8(%r8)
> a: 48 c7 47 08 00 00 00 movq $0x0,0x8(%rdi)
> 11: 00
> 12: 48 rex.W
> 13: c7 .byte 0xc7
> 14: 07 (bad)
> ...
> [ 88.803721] RSP: 0018:ffff9a1f892b7d58 EFLAGS: 00000206
> [ 88.804032] RAX: 0000000000000000 RBX: ffff9a1f8420c800 RCX: ffff9a1f8420c800
> [ 88.804560] RDX: ffff9a1f81bc1440 RSI: 0000000000000000 RDI: 0000000000000000
> [ 88.805056] RBP: ffffffffc04bb0e0 R08: 0000000000000001 R09: 00000000ff7f9a1f
> [ 88.805473] R10: 000000000001001b R11: 0000000000009a1f R12: 0000000000000140
> [ 88.806194] R13: 0000000000000001 R14: ffff9a1f886df400 R15: ffff9a1f886df4ac
> [ 88.806734] FS: 00007f445601a740(0000) GS:ffff9a2e7fd80000(0000) knlGS:0000000000000000
> [ 88.807225] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 88.807672] CR2: 0000000000000000 CR3: 000000050cc46000 CR4: 00000000000006f0
> [ 88.808165] Call Trace:
> [ 88.808459] <TASK>
> [ 88.808710] ? __die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434)
> [ 88.809261] ? page_fault_oops (arch/x86/mm/fault.c:715)
> [ 88.809561] ? exc_page_fault (./arch/x86/include/asm/irqflags.h:26 ./arch/x86/include/asm/irqflags.h:87 ./arch/x86/include/asm/irqflags.h:147 arch/x86/mm/fault.c:1489 arch/x86/mm/fault.c:1539)
> [ 88.809806] ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623)
> [ 88.810074] ? sfq_dequeue (net/sched/sch_sfq.c:272 net/sched/sch_sfq.c:499) sch_sfq
> [ 88.810411] sfq_reset (net/sched/sch_sfq.c:525) sch_sfq
> [ 88.810671] qdisc_reset (./include/linux/skbuff.h:2135 ./include/linux/skbuff.h:2441 ./include/linux/skbuff.h:3304 ./include/linux/skbuff.h:3310 net/sched/sch_generic.c:1036)
> [ 88.810950] tbf_reset (./include/linux/timekeeping.h:169 net/sched/sch_tbf.c:334) sch_tbf
> [ 88.811208] qdisc_reset (./include/linux/skbuff.h:2135 ./include/linux/skbuff.h:2441 ./include/linux/skbuff.h:3304 ./include/linux/skbuff.h:3310 net/sched/sch_generic.c:1036)
> [ 88.811484] netif_set_real_num_tx_queues (./include/linux/spinlock.h:396 ./include/net/sch_generic.h:768 net/core/dev.c:2958)
> [ 88.811870] __tun_detach (drivers/net/tun.c:590 drivers/net/tun.c:673)
> [ 88.812271] tun_chr_close (drivers/net/tun.c:702 drivers/net/tun.c:3517)
> [ 88.812505] __fput (fs/file_table.c:432 (discriminator 1))
> [ 88.812735] task_work_run (kernel/task_work.c:230)
> [ 88.813016] do_exit (kernel/exit.c:940)
> [ 88.813372] ? trace_hardirqs_on (kernel/trace/trace_preemptirq.c:58 (discriminator 4))
> [ 88.813639] ? handle_mm_fault (./arch/x86/include/asm/irqflags.h:42 ./arch/x86/include/asm/irqflags.h:97 ./arch/x86/include/asm/irqflags.h:155 ./include/linux/memcontrol.h:1022 ./include/linux/memcontrol.h:1045 ./include/linux/memcontrol.h:1052 mm/memory.c:5928 mm/memory.c:6088)
> [ 88.813867] do_group_exit (kernel/exit.c:1070)
> [ 88.814138] __x64_sys_exit_group (kernel/exit.c:1099)
> [ 88.814490] x64_sys_call (??:?)
> [ 88.814791] do_syscall_64 (arch/x86/entry/common.c:52 (discriminator 1) arch/x86/entry/common.c:83 (discriminator 1))
> [ 88.815012] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
> [ 88.815495] RIP: 0033:0x7f44560f1975
>
> Fixes: 175f9c1bba9b ("Jussi Kivilinna <jussi.kivilinna@...et.fi>")
Copy/paste error, this should be :
Fixes: 175f9c1bba9b ("net_sched: Add size table for qdiscs")
> Reported-by: syzbot <syzkaller@...glegroups.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> ---
> include/net/sch_generic.h | 1 -
> net/sched/sch_api.c | 7 ++++++-
> 2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> index 79edd5b5e3c9139cac0af251f95cc63e173d05f5..5d74fa7e694cc85be91dbf01f0876b9feaa29115 100644
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -848,7 +848,6 @@ static inline void qdisc_calculate_pkt_len(struct sk_buff *skb,
> static inline int qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> struct sk_buff **to_free)
> {
> - qdisc_calculate_pkt_len(skb, sch);
> return sch->enqueue(skb, sch, to_free);
> }
>
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index 74afc210527d237cca3b48166be5918f802eb326..2eefa4783879971c557ca3d98b74ac1218ea2bd1 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -593,7 +593,6 @@ void __qdisc_calculate_pkt_len(struct sk_buff *skb,
> pkt_len = 1;
> qdisc_skb_cb(skb)->pkt_len = pkt_len;
> }
> -EXPORT_SYMBOL(__qdisc_calculate_pkt_len);
>
> void qdisc_warn_nonwc(const char *txt, struct Qdisc *qdisc)
> {
> @@ -1201,6 +1200,12 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent,
> return -EINVAL;
> }
>
> + if (new &&
> + !(parent->flags & TCQ_F_MQROOT) &&
> + rcu_access_pointer(new->stab)) {
> + NL_SET_ERR_MSG(extack, "STAB not supported on a non root");
> + return -EINVAL;
> + }
> err = cops->graft(parent, cl, new, &old, extack);
> if (err)
> return err;
> --
> 2.47.0.rc0.187.ge670bccf7e-goog
>
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