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Date: Mon, 5 Jun 2023 10:25:20 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <alex.aring@...il.com>, <davem@...emloft.net>, <dsahern@...nel.org>,
<kuba@...nel.org>, <kuni1840@...il.com>, <kuniyu@...zon.com>,
<netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH v1 net] ipv6: rpl: Fix Route of Death.
From: Eric Dumazet <edumazet@...gle.com>
Date: Mon, 5 Jun 2023 19:12:15 +0200
> On Mon, Jun 5, 2023 at 6:48 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> >
> > From: Eric Dumazet <edumazet@...gle.com>
> > Date: Mon, 5 Jun 2023 18:27:46 +0200
> > > On Mon, Jun 5, 2023 at 4:41 PM Kuniyuki Iwashima <kuniyu@...zon.com> wrote:
> > > >
> > > > A remote DoS vulnerability of RPL Source Routing is assigned CVE-2023-2156.
> > > >
> > > > The Source Routing Header (SRH) has the following format:
> > > >
> > > > 0 1 2 3
> > > > 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
> > > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > > > | Next Header | Hdr Ext Len | Routing Type | Segments Left |
> > > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > > > | CmprI | CmprE | Pad | Reserved |
> > > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > > > | |
> > > > . .
> > > > . Addresses[1..n] .
> > > > . .
> > > > | |
> > > > +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
> > > >
> > > > The originator of an SRH places the first hop's IPv6 address in the IPv6
> > > > header's IPv6 Destination Address and the second hop's IPv6 address as
> > > > the first address in Addresses[1..n].
> > > >
> > > > The CmprI and CmprE fields indicate the number of prefix octets that are
> > > > shared with the IPv6 Destination Address. When CmprI or CmprE is not 0,
> > > > Addresses[1..n] are compressed as follows:
> > > >
> > > > 1..n-1 : (16 - CmprI) bytes
> > > > n : (16 - CmprE) bytes
> > > >
> > > > Segments Left indicates the number of route segments remaining. When the
> > > > value is not zero, the SRH is forwarded to the next hop. Its address
> > > > is extracted from Addresses[n - Segment Left + 1] and swapped with IPv6
> > > > Destination Address.
> > > >
> > > > When Segment Left is greater than or equal to 2, the size of SRH is not
> > > > changed because Addresses[1..n-1] are decompressed and recompressed with
> > > > CmprI.
> > > >
> > > > OTOH, when Segment Left changes from 1 to 0, the new SRH could have a
> > > > different size because Addresses[1..n-1] are decompressed with CmprI and
> > > > recompressed with CmprE.
> > > >
> > > > Let's say CmprI is 15 and CmprE is 0. When we receive SRH with Segment
> > > > Left >= 2, Addresses[1..n-1] have 1 byte for each, and Addresses[n] has
> > > > 16 bytes. When Segment Left is 1, Addresses[1..n-1] is decompressed to
> > > > 16 bytes and not recompressed. Finally, the new SRH will need more room
> > > > in the header, and the size is (16 - 1) * (n - 1) bytes.
> > > >
> > > > Here the max value of n is 255 as Segment Left is u8, so in the worst case,
> > > > we have to allocate 3825 bytes in the skb headroom. However, now we only
> > > > allocate a small fixed buffer that is IPV6_RPL_SRH_WORST_SWAP_SIZE (16 + 7
> > > > bytes). If the decompressed size overflows the room, skb_push() hits BUG()
> > > > below [0].
> > > >
> > > > Instead of allocating the fixed buffer for every packet, let's allocate
> > > > enough headroom only when we receive SRH with Segment Left 1.
> > > >
> > > > [0]:
> > > > skbuff: skb_under_panic: text:ffffffff81c9f6e2 len:576 put:576 head:ffff8880070b5180 data:ffff8880070b4fb0 tail:0x70 end:0x140 dev:lo
> > > > kernel BUG at net/core/skbuff.c:200!
> > > > invalid opcode: 0000 [#1] PREEMPT SMP PTI
> > > > CPU: 0 PID: 154 Comm: python3 Not tainted 6.4.0-rc4-00190-gc308e9ec0047 #7
> > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> > > > RIP: 0010:skb_panic (net/core/skbuff.c:200)
> > > > Code: 4f 70 50 8b 87 bc 00 00 00 50 8b 87 b8 00 00 00 50 ff b7 c8 00 00 00 4c 8b 8f c0 00 00 00 48 c7 c7 80 6e 77 82 e8 ad 8b 60 ff <0f> 0b 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90
> > > > RSP: 0018:ffffc90000003da0 EFLAGS: 00000246
> > > > RAX: 0000000000000085 RBX: ffff8880058a6600 RCX: 0000000000000000
> > > > RDX: 0000000000000000 RSI: ffff88807dc1c540 RDI: ffff88807dc1c540
> > > > RBP: ffffc90000003e48 R08: ffffffff82b392c8 R09: 00000000ffffdfff
> > > > R10: ffffffff82a592e0 R11: ffffffff82b092e0 R12: ffff888005b1c800
> > > > R13: ffff8880070b51b8 R14: ffff888005b1ca18 R15: ffff8880070b5190
> > > > FS: 00007f4539f0b740(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
> > > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > > CR2: 000055670baf3000 CR3: 0000000005b0e000 CR4: 00000000007506f0
> > > > PKRU: 55555554
> > > > Call Trace:
> > > > <IRQ>
> > > > skb_push (net/core/skbuff.c:210)
> > > > ipv6_rthdr_rcv (./include/linux/skbuff.h:2880 net/ipv6/exthdrs.c:634 net/ipv6/exthdrs.c:718)
> > > > ? raw6_local_deliver (net/ipv6/raw.c:207)
> > > > ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:437 (discriminator 5))
> > > > ip6_input_finish (./include/linux/rcupdate.h:805 net/ipv6/ip6_input.c:483)
> > > > __netif_receive_skb_one_core (net/core/dev.c:5494)
> > > > process_backlog (./include/linux/rcupdate.h:805 net/core/dev.c:5934)
> > > > __napi_poll (net/core/dev.c:6496)
> > > > net_rx_action (net/core/dev.c:6565 net/core/dev.c:6696)
> > > > __do_softirq (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/irq.h:142 kernel/softirq.c:572)
> > > > do_softirq (kernel/softirq.c:472 kernel/softirq.c:459)
> > > > </IRQ>
> > > > <TASK>
> > > > __local_bh_enable_ip (kernel/softirq.c:396)
> > > > __dev_queue_xmit (net/core/dev.c:4272)
> > > > ip6_finish_output2 (./include/net/neighbour.h:544 net/ipv6/ip6_output.c:134)
> > > > rawv6_sendmsg (./include/net/dst.h:458 ./include/linux/netfilter.h:303 net/ipv6/raw.c:656 net/ipv6/raw.c:914)
> > > > sock_sendmsg (net/socket.c:724 net/socket.c:747)
> > > > __sys_sendto (net/socket.c:2144)
> > > > __x64_sys_sendto (net/socket.c:2156 net/socket.c:2152 net/socket.c:2152)
> > > > do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
> > > > entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
> > > > RIP: 0033:0x7f453a138aea
> > > > Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb b8 0f 1f 00 f3 0f 1e fa 41 89 ca 64 8b 04 25 18 00 00 00 85 c0 75 15 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 7e c3 0f 1f 44 00 00 41 54 48 83 ec 30 44 89
> > > > RSP: 002b:00007ffcc212a1c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
> > > > RAX: ffffffffffffffda RBX: 00007ffcc212a288 RCX: 00007f453a138aea
> > > > RDX: 0000000000000060 RSI: 00007f4539084c20 RDI: 0000000000000003
> > > > RBP: 00007f4538308e80 R08: 00007ffcc212a300 R09: 000000000000001c
> > > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> > > > R13: ffffffffc4653600 R14: 0000000000000001 R15: 00007f4539712d1b
> > > > </TASK>
> > > > Modules linked in:
> > > >
> > > > Fixes: 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr")
> > > > Reported-by: Max VA
> > > > Closes: https://www.interruptlabs.co.uk/articles/linux-ipv6-route-of-death
> > > > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > > > ---
> > > > To maintainers:
> > > > Please complement the Reported-by address from the security@ mailing list
> > > > if possible, which checkpatch will complain about.
> > > > ---
> > > > include/net/rpl.h | 3 ---
> > > > net/ipv6/exthdrs.c | 26 ++++++++------------------
> > > > 2 files changed, 8 insertions(+), 21 deletions(-)
> > > >
> > > > diff --git a/include/net/rpl.h b/include/net/rpl.h
> > > > index 308ef0a05cae..30fe780d1e7c 100644
> > > > --- a/include/net/rpl.h
> > > > +++ b/include/net/rpl.h
> > > > @@ -23,9 +23,6 @@ static inline int rpl_init(void)
> > > > static inline void rpl_exit(void) {}
> > > > #endif
> > > >
> > > > -/* Worst decompression memory usage ipv6 address (16) + pad 7 */
> > > > -#define IPV6_RPL_SRH_WORST_SWAP_SIZE (sizeof(struct in6_addr) + 7)
> > > > -
> > > > size_t ipv6_rpl_srh_size(unsigned char n, unsigned char cmpri,
> > > > unsigned char cmpre);
> > > >
> > > > diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> > > > index a8d961d3a477..bc413961f564 100644
> > > > --- a/net/ipv6/exthdrs.c
> > > > +++ b/net/ipv6/exthdrs.c
> > > > @@ -569,24 +569,6 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
> > > > return -1;
> > > > }
> > > >
> > > > - if (skb_cloned(skb)) {
> > > > - if (pskb_expand_head(skb, IPV6_RPL_SRH_WORST_SWAP_SIZE, 0,
> > > > - GFP_ATOMIC)) {
> > > > - __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
> > > > - IPSTATS_MIB_OUTDISCARDS);
> > > > - kfree_skb(skb);
> > > > - return -1;
> > > > - }
> > > > - } else {
> > > > - err = skb_cow_head(skb, IPV6_RPL_SRH_WORST_SWAP_SIZE);
> > > > - if (unlikely(err)) {
> > > > - kfree_skb(skb);
> > > > - return -1;
> > > > - }
> > > > - }
> > > > -
> > > > - hdr = (struct ipv6_rpl_sr_hdr *)skb_transport_header(skb);
> > > > -
> > > > if (!pskb_may_pull(skb, ipv6_rpl_srh_size(n, hdr->cmpri,
> > > > hdr->cmpre))) {
> > > > kfree_skb(skb);
> > > > @@ -630,6 +612,14 @@ static int ipv6_rpl_srh_rcv(struct sk_buff *skb)
> > > > skb_pull(skb, ((hdr->hdrlen + 1) << 3));
> > > > skb_postpull_rcsum(skb, oldhdr,
> > > > sizeof(struct ipv6hdr) + ((hdr->hdrlen + 1) << 3));
> > > > + if (unlikely(!hdr->segments_left) &&
> > > > + pskb_expand_head(skb, sizeof(struct ipv6hdr) + ((chdr->hdrlen + 1) << 3), 0,
> > > > + GFP_ATOMIC)) {
> > > > + __IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)), IPSTATS_MIB_OUTDISCARDS);
> > > > + kfree_skb(skb);
> > > > + kfree(buf);
> > > > + return -1;
> > > > + }
> > > > skb_push(skb, ((chdr->hdrlen + 1) << 3) + sizeof(struct ipv6hdr));
> > > > skb_reset_network_header(skb);
> > > > skb_mac_header_rebuild(skb);
> > >
> > > Your patch is not complete.
> > >
> > > Any pskb_maypull() or pskb_expand_head() can change skb->head
> > >
> > > So @oldhdr will point to freed memory and this will trigger another bug report.
> > >
> > > memmove(ipv6_hdr(skb), oldhdr, sizeof(struct ipv6hdr)); // crash
> >
> > Yes, I assumed your series would fix it. At least after the new
> > pskb_expand_head(), we don't touch the hdr.
> >
> > If it's the best option, could you take my patch into your v2 ?
> >
>
> I think the existing calls do not change skb->head, because the caller normally
> already pulled the needed data.
Ah exactly, ipv6_rthdr_rcv() already pulled the header and addresses.
Then, I can leave my patch as is.
---8<---
if (!pskb_may_pull(skb, skb_transport_offset(skb) + 8) ||
!pskb_may_pull(skb, (skb_transport_offset(skb) +
((skb_transport_header(skb)[1] + 1) << 3)))) {
__IP6_INC_STATS(net, idev, IPSTATS_MIB_INHDRERRORS);
kfree_skb(skb);
return -1;
}
---8<---
>
> Essentially I think your patch should be standalone.
>
> Later we can cleanup things.
Yes, we can remove them later.
Thanks!
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