On Sun, Dec 10, 2017 at 12:59 AM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote: > On Sat, 2017-12-09 at 19:23 +0800, Xin Long wrote: >> On Fri, Dec 8, 2017 at 4:45 PM, Xin Long <lucien.xin@xxxxxxxxx> >> wrote: >> > On Fri, Dec 8, 2017 at 4:16 PM, syzbot >> > <bot+ed0838d0fa4c4f2b528e20286e6dc63effc7c14d@syzkaller.appspotmail >> > .com> >> > wrote: >> > > syzkaller has found reproducer for the following crash on >> > > 82bcf1def3b5f1251177ad47c44f7e17af039b4b >> > > git://git.cmpxchg.org/linux-mmots.git/master >> > > compiler: gcc (GCC) 7.1.1 20170620 >> > > .config is attached >> > > Raw console output is attached. >> > > >> > > syzkaller reproducer is attached. See https://goo.gl/kgGztJ >> > > for information about syzkaller reproducers >> > > >> > > >> > > skbuff: skb_over_panic: text:0000000010b86b8d len:196 put:20 >> > > head:000000003b477e60 data:000000000e85441e tail:0xd4 end:0xc0 >> > > dev:lo >> > > ------------[ cut here ]------------ >> > > kernel BUG at net/core/skbuff.c:104! >> > > invalid opcode: 0000 [#1] SMP KASAN >> > > Dumping ftrace buffer: >> > > (ftrace buffer empty) >> > > Modules linked in: >> > > CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.15.0-rc2-mm1+ #39 >> > > Hardware name: Google Google Compute Engine/Google Compute >> > > Engine, BIOS >> > > Google 01/01/2011 >> > > RIP: 0010:skb_panic+0x15c/0x1f0 net/core/skbuff.c:100 >> > > RSP: 0018:ffff8801db307508 EFLAGS: 00010286 >> > > RAX: 0000000000000082 RBX: ffff8801c517e840 RCX: 0000000000000000 >> > > RDX: 0000000000000082 RSI: 1ffff1003b660e61 RDI: ffffed003b660e95 >> > > RBP: ffff8801db307570 R08: 1ffff1003b660e23 R09: 0000000000000000 >> > > R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff85bd4020 >> > > R13: ffffffff84754ed2 R14: 0000000000000014 R15: ffff8801c4e26540 >> > > FS: 0000000000000000(0000) GS:ffff8801db300000(0000) >> > > knlGS:0000000000000000 >> > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> > > CR2: 0000000000463610 CR3: 00000001c6698000 CR4: 00000000001406e0 >> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> > > Call Trace: >> > > <IRQ> >> > > skb_over_panic net/core/skbuff.c:109 [inline] >> > > skb_put+0x181/0x1c0 net/core/skbuff.c:1694 >> > > add_grhead.isra.24+0x42/0x3b0 net/ipv6/mcast.c:1695 >> > > add_grec+0xa55/0x1060 net/ipv6/mcast.c:1817 >> > > mld_send_cr net/ipv6/mcast.c:1903 [inline] >> > > mld_ifc_timer_expire+0x4d2/0x770 net/ipv6/mcast.c:2448 >> > > call_timer_fn+0x23b/0x840 kernel/time/timer.c:1320 >> > > expire_timers kernel/time/timer.c:1357 [inline] >> > > __run_timers+0x7e1/0xb60 kernel/time/timer.c:1660 >> > > run_timer_softirq+0x4c/0xb0 kernel/time/timer.c:1686 >> > > __do_softirq+0x29d/0xbb2 kernel/softirq.c:285 >> > > invoke_softirq kernel/softirq.c:365 [inline] >> > > irq_exit+0x1d3/0x210 kernel/softirq.c:405 >> > > exiting_irq arch/x86/include/asm/apic.h:540 [inline] >> > > smp_apic_timer_interrupt+0x16b/0x700 >> > > arch/x86/kernel/apic/apic.c:1052 >> > > apic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:920 >> > > </IRQ> >> > > RIP: 0010:native_safe_halt+0x6/0x10 >> > > arch/x86/include/asm/irqflags.h:54 >> > > RSP: 0018:ffff8801d9f97da8 EFLAGS: 00000282 ORIG_RAX: >> > > ffffffffffffff11 >> > > RAX: dffffc0000000000 RBX: 1ffff1003b3f2fb8 RCX: 0000000000000000 >> > > RDX: 1ffffffff0c59734 RSI: 0000000000000001 RDI: ffffffff862cb9a0 >> > > RBP: ffff8801d9f97da8 R08: 0000000000000000 R09: 0000000000000000 >> > > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001 >> > > R13: ffff8801d9f97e60 R14: ffffffff869eb920 R15: 0000000000000000 >> > > arch_safe_halt arch/x86/include/asm/paravirt.h:93 [inline] >> > > default_idle+0xbf/0x430 arch/x86/kernel/process.c:355 >> > > arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:346 >> > > default_idle_call+0x36/0x90 kernel/sched/idle.c:98 >> > > cpuidle_idle_call kernel/sched/idle.c:156 [inline] >> > > do_idle+0x24a/0x3b0 kernel/sched/idle.c:246 >> > > cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:351 >> > > start_secondary+0x330/0x460 arch/x86/kernel/smpboot.c:277 >> > > secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:237 >> > > Code: 03 0f b6 04 01 84 c0 74 04 3c 03 7e 20 8b 4b 78 41 57 48 c7 >> > > c7 a0 38 >> > > bd 85 52 56 4c 89 ea 41 50 4c 89 e6 45 89 f0 e8 0c b6 3d fd <0f> >> > > 0b 4c 89 4d >> > > b8 4c 89 45 c0 48 89 75 c8 48 89 55 d0 e8 7d 93 >> > > RIP: skb_panic+0x15c/0x1f0 net/core/skbuff.c:100 RSP: >> > > ffff8801db307508 >> > > ---[ end trace 941a8a0f633e271f ]--- >> > > >> > >> > This isn't a sctp problem, but mld's, seems when lo's mtu became 0, >> > it allocs a skb without enough space in add_grec(): >> > if (AVAILABLE(skb) < sizeof(*psrc) + >> > first*sizeof(struct mld2_grec)) { >> > if (truncate && !first) >> > break; /* truncate these */ >> > if (pgr) >> > pgr->grec_nsrcs = htons(scount); >> > if (skb) >> > mld_sendpack(skb); >> > skb = mld_newpack(idev, dev->mtu); <--- >> > >> > I will check this for sure later on both igmp and mld. >> >> Fix: >> --- a/net/ipv6/mcast.c >> +++ b/net/ipv6/mcast.c >> @@ -1766,8 +1766,8 @@ static struct sk_buff *add_grec(struct sk_buff >> *skb, struct ifmcaddr6 *pmc, >> if (isquery) >> psf->sf_gsresp = 0; >> >> - if (AVAILABLE(skb) < sizeof(*psrc) + >> - first*sizeof(struct mld2_grec)) { >> + if (AVAILABLE(skb) < (int)(sizeof(*psrc) + >> + first * sizeof(*pgr))) { >> if (truncate && !first) >> break; /* truncate these */ >> if (pgr) >> @@ -1810,7 +1810,7 @@ static struct sk_buff *add_grec(struct sk_buff >> *skb, struct ifmcaddr6 *pmc, >> return skb; >> if (pmc->mca_crcount || isquery || crsend) { >> /* make sure we have room for group header */ >> - if (skb && AVAILABLE(skb) < sizeof(struct mld2_grec)) { >> + if (skb && AVAILABLE(skb) < (int)sizeof(*pgr)) { >> mld_sendpack(skb); >> skb = NULL; /* add_grhead will get a new one */ >> } >> >> do the same on igmp. > > Thanks for the tentative patch. > > Quite a hack if you ask me. > > I would rather : > > 1) Read dev->mtu once to avoid bad assumptions/surprises. > > 2) Give up if this mtu is too small for IPV6 to be functional. > > Something like : > > > net/ipv6/mcast.c | 25 +++++++++++++++---------- > 1 file changed, 15 insertions(+), 10 deletions(-) > > diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c > index fc6d7d143f2c29aab9a3f56eae02e5337e65a97b..844642682b8363c4c32d329ed92474f834a59618 100644 > --- a/net/ipv6/mcast.c > +++ b/net/ipv6/mcast.c > @@ -1682,16 +1682,16 @@ static int grec_size(struct ifmcaddr6 *pmc, int type, int gdel, int sdel) > } > > static struct sk_buff *add_grhead(struct sk_buff *skb, struct ifmcaddr6 *pmc, > - int type, struct mld2_grec **ppgr) > + int type, struct mld2_grec **ppgr, unsigned int mtu) > { > - struct net_device *dev = pmc->idev->dev; > struct mld2_report *pmr; > struct mld2_grec *pgr; > > - if (!skb) > - skb = mld_newpack(pmc->idev, dev->mtu); > - if (!skb) > - return NULL; > + if (!skb) { > + skb = mld_newpack(pmc->idev, mtu); > + if (!skb) > + return NULL; > + } > pgr = skb_put(skb, sizeof(struct mld2_grec)); > pgr->grec_type = type; > pgr->grec_auxwords = 0; > @@ -1714,10 +1714,15 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ifmcaddr6 *pmc, > struct mld2_grec *pgr = NULL; > struct ip6_sf_list *psf, *psf_next, *psf_prev, **psf_list; > int scount, stotal, first, isquery, truncate; > + unsigned int mtu; > > if (pmc->mca_flags & MAF_NOREPORT) > return skb; > > + mtu = READ_ONCE(dev->mtu); > + if (mtu < IPV6_MIN_MTU) > + return skb; > + > isquery = type == MLD2_MODE_IS_INCLUDE || > type == MLD2_MODE_IS_EXCLUDE; > truncate = type == MLD2_MODE_IS_EXCLUDE || > @@ -1738,7 +1743,7 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ifmcaddr6 *pmc, > AVAILABLE(skb) < grec_size(pmc, type, gdeleted, sdeleted)) { > if (skb) > mld_sendpack(skb); > - skb = mld_newpack(idev, dev->mtu); > + skb = mld_newpack(idev, mtu); > } > } > first = 1; > @@ -1774,12 +1779,12 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ifmcaddr6 *pmc, > pgr->grec_nsrcs = htons(scount); > if (skb) > mld_sendpack(skb); > - skb = mld_newpack(idev, dev->mtu); > + skb = mld_newpack(idev, mtu); > first = 1; > scount = 0; > } > if (first) { > - skb = add_grhead(skb, pmc, type, &pgr); > + skb = add_grhead(skb, pmc, type, &pgr, mtu); > first = 0; > } > if (!skb) > @@ -1814,7 +1819,7 @@ static struct sk_buff *add_grec(struct sk_buff *skb, struct ifmcaddr6 *pmc, > mld_sendpack(skb); > skb = NULL; /* add_grhead will get a new one */ > } > - skb = add_grhead(skb, pmc, type, &pgr); > + skb = add_grhead(skb, pmc, type, &pgr, mtu); > } > } > if (pgr) > The new patch works to me, just two questions: 1. should it use "idev->cnf.mtu6" here for mld ? 2. 'if (int < unsigned int)' is still not nice, though in 'if (AVAILABLE(skb) < sizeof())' AVAILABLE(skb) seems always to return >= 0 after your patch. -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
