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Date: Mon, 5 Jun 2023 18:27:46 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, David Ahern <dsahern@...nel.org>,
Alexander Aring <alex.aring@...il.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v1 net] ipv6: rpl: Fix Route of Death.
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
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