Syzbot found a kernel bug in the ipv6 stack:
LINK: https://syzkaller.appspot.com/bug?id=205d6f11d72329ab8d62a610c44c5e7e25415580
The reproducer triggers it by sending an invalid message via sendmmsg() call,
which triggers skb_over_panic, and crashes the kernel:
skbuff: skb_over_panic: text:ffffffff84647fb4 len:65575 put:65575
head:ffff888109ff0000 data:ffff888109ff0088 tail:0x100af end:0xfec0
dev:<NULL>
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:113!
PREEMPT SMP KASAN
CPU: 1 PID: 1818 Comm: repro Not tainted 5.17.0-rc7-dirty #9
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
RIP: 0010:skb_panic+0x173/0x175
RSP: 0018:ffffc900015bf3b8 EFLAGS: 00010282
RAX: 0000000000000090 RBX: ffff88810e848c80 RCX: 0000000000000000
RDX: ffff88810fd84300 RSI: ffffffff814fa5ef RDI: fffff520002b7e69
RBP: ffffc900015bf420 R08: 0000000000000090 R09: 0000000000000000
R10: ffffffff814f55f4 R11: 203a666675626b73 R12: ffffffff855bff80
R13: ffffffff84647fb4 R14: 0000000000010027 R15: ffffffff855bf420
FS: 0000000000c8b3c0(0000) GS:ffff88811b100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000040 CR3: 0000000106b68000 CR4: 0000000000150ea0
Call Trace:
<TASK>
skb_put.cold+0x23/0x23
__ip6_append_data.isra.0.cold+0x396/0xe3a
ip6_append_data+0x1e5/0x320
rawv6_sendmsg.cold+0x1618/0x2ba9
inet_sendmsg+0x9e/0xe0
sock_sendmsg+0xd7/0x130
____sys_sendmsg+0x381/0x8a0
___sys_sendmsg+0x100/0x170
__sys_sendmmsg+0x26c/0x3b7
__x64_sys_sendmmsg+0xb2/0xbd
do_syscall_64+0x35/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xae
The reproducer can be found here:
LINK: https://syzkaller.appspot.com/text?tag=ReproC&x=1648c83fb00000
This can be fixed by increasing the alloclen in case it is smaller than
fraglen in __ip6_append_data().
Cc: David S. Miller <[email protected]>
Cc: Hideaki YOSHIFUJI <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: KP Singh <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Reported-by: [email protected]
Signed-off-by: Tadeusz Struk <[email protected]>
---
net/ipv6/ip6_output.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 4788f6b37053..622345af323e 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1629,6 +1629,13 @@ static int __ip6_append_data(struct sock *sk,
err = -EINVAL;
goto error;
}
+ if (unlikely(alloclen < fraglen)) {
+ if (printk_ratelimit())
+ pr_warn("%s: wrong alloclen: %d, fraglen: %d",
+ __func__, alloclen, fraglen);
+ alloclen = fraglen;
+ }
+
if (transhdrlen) {
skb = sock_alloc_send_skb(sk, alloclen,
(flags & MSG_DONTWAIT), &err);
--
2.35.1
From: Tadeusz Struk
> Sent: 08 March 2022 00:02
>
> Syzbot found a kernel bug in the ipv6 stack:
> LINK: https://syzkaller.appspot.com/bug?id=205d6f11d72329ab8d62a610c44c5e7e25415580
>
> The reproducer triggers it by sending an invalid message via sendmmsg() call,
> which triggers skb_over_panic, and crashes the kernel:
>
> skbuff: skb_over_panic: text:ffffffff84647fb4 len:65575 put:65575
> head:ffff888109ff0000 data:ffff888109ff0088 tail:0x100af end:0xfec0
> dev:<NULL>
>
> ------------[ cut here ]------------
> kernel BUG at net/core/skbuff.c:113!
> PREEMPT SMP KASAN
> CPU: 1 PID: 1818 Comm: repro Not tainted 5.17.0-rc7-dirty #9
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
> RIP: 0010:skb_panic+0x173/0x175
> RSP: 0018:ffffc900015bf3b8 EFLAGS: 00010282
> RAX: 0000000000000090 RBX: ffff88810e848c80 RCX: 0000000000000000
> RDX: ffff88810fd84300 RSI: ffffffff814fa5ef RDI: fffff520002b7e69
> RBP: ffffc900015bf420 R08: 0000000000000090 R09: 0000000000000000
> R10: ffffffff814f55f4 R11: 203a666675626b73 R12: ffffffff855bff80
> R13: ffffffff84647fb4 R14: 0000000000010027 R15: ffffffff855bf420
> FS: 0000000000c8b3c0(0000) GS:ffff88811b100000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000040 CR3: 0000000106b68000 CR4: 0000000000150ea0
> Call Trace:
> <TASK>
> skb_put.cold+0x23/0x23
> __ip6_append_data.isra.0.cold+0x396/0xe3a
> ip6_append_data+0x1e5/0x320
> rawv6_sendmsg.cold+0x1618/0x2ba9
> inet_sendmsg+0x9e/0xe0
> sock_sendmsg+0xd7/0x130
> ____sys_sendmsg+0x381/0x8a0
> ___sys_sendmsg+0x100/0x170
> __sys_sendmmsg+0x26c/0x3b7
> __x64_sys_sendmmsg+0xb2/0xbd
> do_syscall_64+0x35/0xb0
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> The reproducer can be found here:
> LINK: https://syzkaller.appspot.com/text?tag=ReproC&x=1648c83fb00000
> This can be fixed by increasing the alloclen in case it is smaller than
> fraglen in __ip6_append_data().
>
>
> Reported-by: [email protected]
> Signed-off-by: Tadeusz Struk <[email protected]>
> ---
> net/ipv6/ip6_output.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 4788f6b37053..622345af323e 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1629,6 +1629,13 @@ static int __ip6_append_data(struct sock *sk,
> err = -EINVAL;
> goto error;
> }
> + if (unlikely(alloclen < fraglen)) {
> + if (printk_ratelimit())
> + pr_warn("%s: wrong alloclen: %d, fraglen: %d",
> + __func__, alloclen, fraglen);
> + alloclen = fraglen;
> + }
> +
Except that is a valid case, see a few lines higher:
alloclen = min_t(int, fraglen, MAX_HEADER);
pagedlen = fraglen - alloclen;
You need to report the input values that cause the problem later on.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
On 3/8/22 8:43 AM, Tadeusz Struk wrote:
> Hi David,
> On 3/7/22 18:58, David Laight wrote:
>>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>>> index 4788f6b37053..622345af323e 100644
>>> --- a/net/ipv6/ip6_output.c
>>> +++ b/net/ipv6/ip6_output.c
>>> @@ -1629,6 +1629,13 @@ static int __ip6_append_data(struct sock *sk,
>>> err = -EINVAL;
>>> goto error;
>>> }
>>> + if (unlikely(alloclen < fraglen)) {
>>> + if (printk_ratelimit())
>>> + pr_warn("%s: wrong alloclen: %d, fraglen: %d",
>>> + __func__, alloclen, fraglen);
>>> + alloclen = fraglen;
>>> + }
>>> +
>> Except that is a valid case, see a few lines higher:
>>
>> alloclen = min_t(int, fraglen, MAX_HEADER);
>> pagedlen = fraglen - alloclen;
>>
>> You need to report the input values that cause the problem later on.
>
> OK, but in this case it falls into the first if block:
> https://elixir.bootlin.com/linux/v5.17-rc7/source/net/ipv6/ip6_output.c#L1606
>
> where alloclen is assigned the value of mtu.
> The values in this case are just before the alloc_skb() are:
>
> alloclen = 1480
> alloc_extra = 136
> datalen = 64095
> fragheaderlen = 1480
> fraglen = 65575
> transhdrlen = 0
> mtu = 1480
>
Does this solve the problem (whitespace damaged on paste, but it is just
a code move and removing fraglen getting set twice):
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index e69fac576970..59f036241f1b 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1589,6 +1589,15 @@ static int __ip6_append_data(struct sock *sk,
if (datalen > (cork->length <= mtu &&
!(cork->flags & IPCORK_ALLFRAG) ? mtu : maxfraglen) - fragheaderlen)
datalen = maxfraglen - fragheaderlen -
rt->dst.trailer_len;
+
+ if (datalen != length + fraggap) {
+ /*
+ * this is not the last fragment, the
trailer
+ * space is regarded as data space.
+ */
+ datalen += rt->dst.trailer_len;
+ }
+
fraglen = datalen + fragheaderlen;
pagedlen = 0;
@@ -1615,16 +1624,6 @@ static int __ip6_append_data(struct sock *sk,
}
alloclen += alloc_extra;
- if (datalen != length + fraggap) {
- /*
- * this is not the last fragment, the
trailer
- * space is regarded as data space.
- */
- datalen += rt->dst.trailer_len;
- }
-
- fraglen = datalen + fragheaderlen;
-
copy = datalen - transhdrlen - fraggap - pagedlen;
if (copy < 0) {
err = -EINVAL;
On 3/8/22 10:18, David Ahern wrote:
>> alloclen = 1480
>> alloc_extra = 136
>> datalen = 64095
>> fragheaderlen = 1480
>> fraglen = 65575
>> transhdrlen = 0
>> mtu = 1480
>>
> Does this solve the problem (whitespace damaged on paste, but it is just
> a code move and removing fraglen getting set twice):
>
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index e69fac576970..59f036241f1b 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -1589,6 +1589,15 @@ static int __ip6_append_data(struct sock *sk,
>
> if (datalen > (cork->length <= mtu &&
> !(cork->flags & IPCORK_ALLFRAG) ? mtu : maxfraglen) - fragheaderlen)
> datalen = maxfraglen - fragheaderlen -
> rt->dst.trailer_len;
> +
> + if (datalen != length + fraggap) {
> + /*
> + * this is not the last fragment, the
> trailer
> + * space is regarded as data space.
> + */
> + datalen += rt->dst.trailer_len;
> + }
> +
> fraglen = datalen + fragheaderlen;
> pagedlen = 0;
>
> @@ -1615,16 +1624,6 @@ static int __ip6_append_data(struct sock *sk,
> }
> alloclen += alloc_extra;
>
> - if (datalen != length + fraggap) {
> - /*
> - * this is not the last fragment, the
> trailer
> - * space is regarded as data space.
> - */
> - datalen += rt->dst.trailer_len;
> - }
> -
> - fraglen = datalen + fragheaderlen;
> -
> copy = datalen - transhdrlen - fraggap - pagedlen;
> if (copy < 0) {
> err = -EINVAL;
That fails in the same way:
skbuff: skb_over_panic: text:ffffffff83e7b48b len:65575 put:65575
head:ffff888101f8a000 data:ffff888101f8a088 tail:0x100af end:0x6c0 dev:<NULL>
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:113!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 1852 Comm: repro Not tainted 5.17.0-rc7-00020-gea4424be1688-dirty #19
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
RIP: 0010:skb_panic+0x173/0x175
I'm not sure how it supposed to help since it doesn't change the alloclen at all.
I think the problem here is that the size of the allocated skb is too small.
--
Thanks,
Tadeusz
Hi David,
On 3/7/22 18:58, David Laight wrote:
>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>> index 4788f6b37053..622345af323e 100644
>> --- a/net/ipv6/ip6_output.c
>> +++ b/net/ipv6/ip6_output.c
>> @@ -1629,6 +1629,13 @@ static int __ip6_append_data(struct sock *sk,
>> err = -EINVAL;
>> goto error;
>> }
>> + if (unlikely(alloclen < fraglen)) {
>> + if (printk_ratelimit())
>> + pr_warn("%s: wrong alloclen: %d, fraglen: %d",
>> + __func__, alloclen, fraglen);
>> + alloclen = fraglen;
>> + }
>> +
> Except that is a valid case, see a few lines higher:
>
> alloclen = min_t(int, fraglen, MAX_HEADER);
> pagedlen = fraglen - alloclen;
>
> You need to report the input values that cause the problem later on.
OK, but in this case it falls into the first if block:
https://elixir.bootlin.com/linux/v5.17-rc7/source/net/ipv6/ip6_output.c#L1606
where alloclen is assigned the value of mtu.
The values in this case are just before the alloc_skb() are:
alloclen = 1480
alloc_extra = 136
datalen = 64095
fragheaderlen = 1480
fraglen = 65575
transhdrlen = 0
mtu = 1480
--
Thanks,
Tadeusz
On 3/8/22 12:46 PM, Tadeusz Struk wrote:
> That fails in the same way:
>
> skbuff: skb_over_panic: text:ffffffff83e7b48b len:65575 put:65575
> head:ffff888101f8a000 data:ffff888101f8a088 tail:0x100af end:0x6c0
> dev:<NULL>
> ------------[ cut here ]------------
> kernel BUG at net/core/skbuff.c:113!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 1852 Comm: repro Not tainted
> 5.17.0-rc7-00020-gea4424be1688-dirty #19
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
> RIP: 0010:skb_panic+0x173/0x175
>
> I'm not sure how it supposed to help since it doesn't change the
> alloclen at all.
alloclen is a function of fraglen and fraglen is a function of datalen.
On 3/8/22 21:01, David Ahern wrote:
> On 3/8/22 12:46 PM, Tadeusz Struk wrote:
>> That fails in the same way:
>>
>> skbuff: skb_over_panic: text:ffffffff83e7b48b len:65575 put:65575
>> head:ffff888101f8a000 data:ffff888101f8a088 tail:0x100af end:0x6c0
>> dev:<NULL>
>> ------------[ cut here ]------------
>> kernel BUG at net/core/skbuff.c:113!
>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>> CPU: 0 PID: 1852 Comm: repro Not tainted
>> 5.17.0-rc7-00020-gea4424be1688-dirty #19
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
>> RIP: 0010:skb_panic+0x173/0x175
>>
>> I'm not sure how it supposed to help since it doesn't change the
>> alloclen at all.
>
> alloclen is a function of fraglen and fraglen is a function of datalen.
Ok, but in this case it doesn't affect the alloclen and it still fails.
--
Thanks,
Tadeusz
On Thu, Mar 10, 2022 at 11:06 AM Tadeusz Struk <[email protected]> wrote:
>
> On 3/10/22 06:39, Willem de Bruijn wrote:
> > On Wed, Mar 9, 2022 at 4:37 PM Tadeusz Struk <[email protected]> wrote:
> >>
> >> On 3/8/22 21:01, David Ahern wrote:
> >>> On 3/8/22 12:46 PM, Tadeusz Struk wrote:
> >>>> That fails in the same way:
> >>>>
> >>>> skbuff: skb_over_panic: text:ffffffff83e7b48b len:65575 put:65575
> >>>> head:ffff888101f8a000 data:ffff888101f8a088 tail:0x100af end:0x6c0
> >>>> dev:<NULL>
> >>>> ------------[ cut here ]------------
> >>>> kernel BUG at net/core/skbuff.c:113!
> >>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> >>>> CPU: 0 PID: 1852 Comm: repro Not tainted
> >>>> 5.17.0-rc7-00020-gea4424be1688-dirty #19
> >>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
> >>>> RIP: 0010:skb_panic+0x173/0x175
> >>>>
> >>>> I'm not sure how it supposed to help since it doesn't change the
> >>>> alloclen at all.
> >>>
> >>> alloclen is a function of fraglen and fraglen is a function of datalen.
> >>
> >> Ok, but in this case it doesn't affect the alloclen and it still fails.
> >
> > This is some kind of non-standard packet that is being constructed. Do
> > we understand how it is different?
> >
> > The .syz reproducer is generally a bit more readable than the .c
> > equivalent. Though not as much as an strace of the binary, if you
> > can share that.
> >
> > r0 = socket$inet6_icmp_raw(0xa, 0x3, 0x3a)
> > connect$inet6(r0, &(0x7f0000000040)={0xa, 0x0, 0x0, @dev, 0x6}, 0x1c)
> > setsockopt$inet6_IPV6_HOPOPTS(r0, 0x29, 0x36,
> > &(0x7f0000000100)=ANY=[@ANYBLOB="52b3"], 0x5a0)
> > sendmmsg$inet(r0, &(0x7f00000002c0)=[{{0x0, 0x0,
> > &(0x7f0000000000)=[{&(0x7f00000000c0)="1d2d", 0xfa5f}], 0x1}}], 0x1,
> > 0xfe80)
>
> Here it is:
> https://termbin.com/krtr
> It won't be of much help, I'm afraid, as the offending sendmmsg()
> call isn't fully printed.
Thanks. It does offer some hints on the other two syscalls:
[pid 644] connect(3, {sa_family=AF_INET6, sin6_port=htons(0),
sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "fe80::", &sin6_addr),
sin6_scope_id=if_nametoindex("tunl0")}, 28) = 0
[pid 644] setsockopt(3, SOL_IPV6, IPV6_HOPOPTS,
"R\263\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
1440) = 0
IPV6_HOPOPTS is ns_capable CAP_NET_RAW.
So this adds 1440 bytes to opt_nflen, which is included in
fragheaderlen, causing that to be exactly mtu. This means that the
payload can never be sent, as each fragment header eats up the entire
mtu? This is without any transport headers that would only be part of
the first fragment (which go into opt_flen).
If you can maybe catch the error before the skb_put and just return
EINVAL, we might see whether sendmmsg is relevant or a simple send
would be equivalent. (not super important, that appears unrelated.)
On 3/10/22 06:39, Willem de Bruijn wrote:
> On Wed, Mar 9, 2022 at 4:37 PM Tadeusz Struk <[email protected]> wrote:
>>
>> On 3/8/22 21:01, David Ahern wrote:
>>> On 3/8/22 12:46 PM, Tadeusz Struk wrote:
>>>> That fails in the same way:
>>>>
>>>> skbuff: skb_over_panic: text:ffffffff83e7b48b len:65575 put:65575
>>>> head:ffff888101f8a000 data:ffff888101f8a088 tail:0x100af end:0x6c0
>>>> dev:<NULL>
>>>> ------------[ cut here ]------------
>>>> kernel BUG at net/core/skbuff.c:113!
>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>>>> CPU: 0 PID: 1852 Comm: repro Not tainted
>>>> 5.17.0-rc7-00020-gea4424be1688-dirty #19
>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
>>>> RIP: 0010:skb_panic+0x173/0x175
>>>>
>>>> I'm not sure how it supposed to help since it doesn't change the
>>>> alloclen at all.
>>>
>>> alloclen is a function of fraglen and fraglen is a function of datalen.
>>
>> Ok, but in this case it doesn't affect the alloclen and it still fails.
>
> This is some kind of non-standard packet that is being constructed. Do
> we understand how it is different?
>
> The .syz reproducer is generally a bit more readable than the .c
> equivalent. Though not as much as an strace of the binary, if you
> can share that.
>
> r0 = socket$inet6_icmp_raw(0xa, 0x3, 0x3a)
> connect$inet6(r0, &(0x7f0000000040)={0xa, 0x0, 0x0, @dev, 0x6}, 0x1c)
> setsockopt$inet6_IPV6_HOPOPTS(r0, 0x29, 0x36,
> &(0x7f0000000100)=ANY=[@ANYBLOB="52b3"], 0x5a0)
> sendmmsg$inet(r0, &(0x7f00000002c0)=[{{0x0, 0x0,
> &(0x7f0000000000)=[{&(0x7f00000000c0)="1d2d", 0xfa5f}], 0x1}}], 0x1,
> 0xfe80)
Here it is:
https://termbin.com/krtr
It won't be of much help, I'm afraid, as the offending sendmmsg()
call isn't fully printed.
--
Thanks,
Tadeusz
On 3/10/22 09:32, Willem de Bruijn wrote:
> On Thu, Mar 10, 2022 at 11:06 AM Tadeusz Struk <[email protected]> wrote:
>>
>> On 3/10/22 06:39, Willem de Bruijn wrote:
>>> On Wed, Mar 9, 2022 at 4:37 PM Tadeusz Struk <[email protected]> wrote:
>>>>
>>>> On 3/8/22 21:01, David Ahern wrote:
>>>>> On 3/8/22 12:46 PM, Tadeusz Struk wrote:
>>>>>> That fails in the same way:
>>>>>>
>>>>>> skbuff: skb_over_panic: text:ffffffff83e7b48b len:65575 put:65575
>>>>>> head:ffff888101f8a000 data:ffff888101f8a088 tail:0x100af end:0x6c0
>>>>>> dev:<NULL>
>>>>>> ------------[ cut here ]------------
>>>>>> kernel BUG at net/core/skbuff.c:113!
>>>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>>>>>> CPU: 0 PID: 1852 Comm: repro Not tainted
>>>>>> 5.17.0-rc7-00020-gea4424be1688-dirty #19
>>>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
>>>>>> RIP: 0010:skb_panic+0x173/0x175
>>>>>>
>>>>>> I'm not sure how it supposed to help since it doesn't change the
>>>>>> alloclen at all.
>>>>>
>>>>> alloclen is a function of fraglen and fraglen is a function of datalen.
>>>>
>>>> Ok, but in this case it doesn't affect the alloclen and it still fails.
>>>
>>> This is some kind of non-standard packet that is being constructed. Do
>>> we understand how it is different?
>>>
>>> The .syz reproducer is generally a bit more readable than the .c
>>> equivalent. Though not as much as an strace of the binary, if you
>>> can share that.
>>>
>>> r0 = socket$inet6_icmp_raw(0xa, 0x3, 0x3a)
>>> connect$inet6(r0, &(0x7f0000000040)={0xa, 0x0, 0x0, @dev, 0x6}, 0x1c)
>>> setsockopt$inet6_IPV6_HOPOPTS(r0, 0x29, 0x36,
>>> &(0x7f0000000100)=ANY=[@ANYBLOB="52b3"], 0x5a0)
>>> sendmmsg$inet(r0, &(0x7f00000002c0)=[{{0x0, 0x0,
>>> &(0x7f0000000000)=[{&(0x7f00000000c0)="1d2d", 0xfa5f}], 0x1}}], 0x1,
>>> 0xfe80)
>>
>> Here it is:
>> https://termbin.com/krtr
>> It won't be of much help, I'm afraid, as the offending sendmmsg()
>> call isn't fully printed.
>
> Thanks. It does offer some hints on the other two syscalls:
>
> [pid 644] connect(3, {sa_family=AF_INET6, sin6_port=htons(0),
> sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "fe80::", &sin6_addr),
> sin6_scope_id=if_nametoindex("tunl0")}, 28) = 0
> [pid 644] setsockopt(3, SOL_IPV6, IPV6_HOPOPTS,
> "R\263\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
> 1440) = 0
>
> IPV6_HOPOPTS is ns_capable CAP_NET_RAW.
>
> So this adds 1440 bytes to opt_nflen, which is included in
> fragheaderlen, causing that to be exactly mtu. This means that the
> payload can never be sent, as each fragment header eats up the entire
> mtu? This is without any transport headers that would only be part of
> the first fragment (which go into opt_flen).
>
> If you can maybe catch the error before the skb_put and just return
> EINVAL, we might see whether sendmmsg is relevant or a simple send
> would be equivalent. (not super important, that appears unrelated.)
Do you mean something like this:
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 622345af323e..6d45112322a0 100644
@@ -1656,6 +1649,16 @@ static int __ip6_append_data(struct sock *sk,
skb->protocol = htons(ETH_P_IPV6);
skb->ip_summed = csummode;
skb->csum = 0;
+
+ /*
+ * Check if there is still room for the payload
+ */
+ if (fragheaderlen >= mtu) {
+ err = -EMSGSIZE;
+ kfree_skb(skb);
+ goto error;
+ }
+
/* reserve for fragmentation and ipsec header */
skb_reserve(skb, hh_len + sizeof(struct frag_hdr) +
dst_exthdrlen);
That works as well.
--
Thanks,
Tadeusz
On Wed, Mar 9, 2022 at 4:37 PM Tadeusz Struk <[email protected]> wrote:
>
> On 3/8/22 21:01, David Ahern wrote:
> > On 3/8/22 12:46 PM, Tadeusz Struk wrote:
> >> That fails in the same way:
> >>
> >> skbuff: skb_over_panic: text:ffffffff83e7b48b len:65575 put:65575
> >> head:ffff888101f8a000 data:ffff888101f8a088 tail:0x100af end:0x6c0
> >> dev:<NULL>
> >> ------------[ cut here ]------------
> >> kernel BUG at net/core/skbuff.c:113!
> >> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> >> CPU: 0 PID: 1852 Comm: repro Not tainted
> >> 5.17.0-rc7-00020-gea4424be1688-dirty #19
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
> >> RIP: 0010:skb_panic+0x173/0x175
> >>
> >> I'm not sure how it supposed to help since it doesn't change the
> >> alloclen at all.
> >
> > alloclen is a function of fraglen and fraglen is a function of datalen.
>
> Ok, but in this case it doesn't affect the alloclen and it still fails.
This is some kind of non-standard packet that is being constructed. Do
we understand how it is different?
The .syz reproducer is generally a bit more readable than the .c
equivalent. Though not as much as an strace of the binary, if you
can share that.
r0 = socket$inet6_icmp_raw(0xa, 0x3, 0x3a)
connect$inet6(r0, &(0x7f0000000040)={0xa, 0x0, 0x0, @dev, 0x6}, 0x1c)
setsockopt$inet6_IPV6_HOPOPTS(r0, 0x29, 0x36,
&(0x7f0000000100)=ANY=[@ANYBLOB="52b3"], 0x5a0)
sendmmsg$inet(r0, &(0x7f00000002c0)=[{{0x0, 0x0,
&(0x7f0000000000)=[{&(0x7f00000000c0)="1d2d", 0xfa5f}], 0x1}}], 0x1,
0xfe80)
Syzbot found a kernel bug in the ipv6 stack:
LINK: https://syzkaller.appspot.com/bug?id=205d6f11d72329ab8d62a610c44c5e7e25415580
The reproducer triggers it by sending a crafted message via sendmmsg()
call, which triggers skb_over_panic, and crashes the kernel:
skbuff: skb_over_panic: text:ffffffff84647fb4 len:65575 put:65575
head:ffff888109ff0000 data:ffff888109ff0088 tail:0x100af end:0xfec0
dev:<NULL>
Add a check that prevents an invalid packet with MTU equall to the
fregment header size to eat up all the space for payload.
The reproducer can be found here:
LINK: https://syzkaller.appspot.com/text?tag=ReproC&x=1648c83fb00000
Cc: Willem de Bruijn <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Hideaki YOSHIFUJI <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Martin KaFai Lau <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Yonghong Song <[email protected]>
Cc: John Fastabend <[email protected]>
Cc: KP Singh <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Reported-by: [email protected]
Signed-off-by: Tadeusz Struk <[email protected]>
---
v2: Instead of updating the alloclen add a check that prevents
an invalid packet with MTU equall to the fregment header size
to eat up all the space for payload.
Fix suggested by Willem de Bruijn <[email protected]>
---
net/ipv6/ip6_output.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 4788f6b37053..6d45112322a0 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1649,6 +1649,16 @@ static int __ip6_append_data(struct sock *sk,
skb->protocol = htons(ETH_P_IPV6);
skb->ip_summed = csummode;
skb->csum = 0;
+
+ /*
+ * Check if there is still room for payload
+ */
+ if (fragheaderlen >= mtu) {
+ err = -EMSGSIZE;
+ kfree_skb(skb);
+ goto error;
+ }
+
/* reserve for fragmentation and ipsec header */
skb_reserve(skb, hh_len + sizeof(struct frag_hdr) +
dst_exthdrlen);
--
2.35.1