Re: kernel BUG at net/core/skbuff.c:LINE! (2)
From: Eric Dumazet
Date: Sat Dec 09 2017 - 11:59:57 EST
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@xxxxxxxxxxxxxxxxxxxxx
> > .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:
> > > ÂÂÂ(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:ÂÂ0000000000000000(0000) GS:ffff8801db300000(0000)
> > > knlGS:0000000000000000
> > > CS:ÂÂ0010 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:
> > > Â<IRQ>
> > > Âskb_over_panic net/core/skbuff.c:109 [inline]
> > > Âskb_put+0x181/0x1c0 net/core/skbuff.c:1694
> > > Âadd_grhead.isra.24+0x42/0x3b0 net/ipv6/mcast.c:1695
> > > Âadd_grec+0xa55/0x1060 net/ipv6/mcast.c:1817
> > > Âmld_send_cr net/ipv6/mcast.c:1903 [inline]
> > > Âmld_ifc_timer_expire+0x4d2/0x770 net/ipv6/mcast.c:2448
> > > Âcall_timer_fn+0x23b/0x840 kernel/time/timer.c:1320
> > > Âexpire_timers kernel/time/timer.c:1357 [inline]
> > > Â__run_timers+0x7e1/0xb60 kernel/time/timer.c:1660
> > > Ârun_timer_softirq+0x4c/0xb0 kernel/time/timer.c:1686
> > > Â__do_softirq+0x29d/0xbb2 kernel/softirq.c:285
> > > Âinvoke_softirq kernel/softirq.c:365 [inline]
> > > Âirq_exit+0x1d3/0x210 kernel/softirq.c:405
> > > Âexiting_irq arch/x86/include/asm/apic.h:540 [inline]
> > > Âsmp_apic_timer_interrupt+0x16b/0x700
> > > arch/x86/kernel/apic/apic.c:1052
> > > Âapic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:920
> > > Â</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
> > > Âarch_safe_halt arch/x86/include/asm/paravirt.h:93 [inline]
> > > Âdefault_idle+0xbf/0x430 arch/x86/kernel/process.c:355
> > > Âarch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:346
> > > Âdefault_idle_call+0x36/0x90 kernel/sched/idle.c:98
> > > Âcpuidle_idle_call kernel/sched/idle.c:156 [inline]
> > > Âdo_idle+0x24a/0x3b0 kernel/sched/idle.c:246
> > > Âcpu_startup_entry+0x18/0x20 kernel/sched/idle.c:351
> > > Âstart_secondary+0x330/0x460 arch/x86/kernel/smpboot.c:277
> > > Âsecondary_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():
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (AVAILABLE(skb) < sizeof(*psrc) +
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂfirst*sizeof(struct mld2_grec)) {
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (truncate && !first)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂbreak;ÂÂÂ/* truncate these */
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (pgr)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂpgr->grec_nsrcs = htons(scount);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (skb)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂmld_sendpack(skb);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂskb = 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,
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (isquery)
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂpsf->sf_gsresp = 0;
>
> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (AVAILABLE(skb) < sizeof(*psrc) +
> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂfirst*sizeof(struct mld2_grec)) {
> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (AVAILABLE(skb) < (int)(sizeof(*psrc) +
> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂfirst * sizeof(*pgr))) {
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (truncate && !first)
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂbreak;ÂÂÂ/* truncate these */
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (pgr)
> @@ -1810,7 +1810,7 @@ static struct sk_buff *add_grec(struct sk_buff
> *skb, struct ifmcaddr6 *pmc,
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂreturn skb;
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (pmc->mca_crcount || isquery || crsend) {
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ/* make sure we have room for group header */
> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (skb && AVAILABLE(skb) < sizeof(struct mld2_grec)) {
> +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂif (skb && AVAILABLE(skb) < (int)sizeof(*pgr)) {
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂmld_sendpack(skb);
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂskb = NULL; /* add_grhead will get a new one */
> ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ}
>
> 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)