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Message-ID: <20230719212709.63492-1-kuniyu@amazon.com>
Date: Wed, 19 Jul 2023 14:27:09 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <willemdebruijn.kernel@...il.com>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <gustavoars@...nel.org>,
<keescook@...omium.org>, <kuba@...nel.org>, <kuni1840@...il.com>,
<kuniyu@...zon.com>, <leitao@...ian.org>, <netdev@...r.kernel.org>,
<pabeni@...hat.com>, <syzkaller@...glegroups.com>
Subject: RE: [PATCH v1 net 2/2] af_packet: Fix warning of fortified memcpy() in packet_getname().
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Wed, 19 Jul 2023 17:15:09 -0400
> Kuniyuki Iwashima wrote:
> > syzkaller found a warning in packet_getname() [0], where we try to
> > copy 16 bytes to sockaddr_ll.sll_addr[8].
> >
> > Some devices (ip6gre, vti6, ip6tnl) have 16 bytes address expressed
> > by struct in6_addr.
>
> Some are even larger. MAX_ADDR_LEN == 32. I think Infiniband may use
> that?
Exactly, I didn't know that.
>
> > The write seems to overflow, but actually not since we use struct
> > sockaddr_storage defined in __sys_getsockname().
>
> Which gives _K_SS_MAXSIZE == 128, minus offsetof(struct sockaddr_ll, sll_addr).
>
> For fun, there is another caller. getsockopt SO_PEERNAME also calls
> sock->ops->getname, with a buffer hardcoded to 128. Should probably
> use sizeof(sockaddr_storage) for documentation, at least.
>
> .. and I just noticed that that was attempted, but not completed
> https://lore.kernel.org/lkml/20140928135545.GA23220@type.youpi.perso.aquilenet.fr/
Yes, acutally my first draft had the diff below, but I dropped it
because packet_getname() does not call memcpy() for SO_PEERNAME at
least, and same for getpeername().
And interestingly there was a revival thread.
https://lore.kernel.org/netdev/20230719084415.1378696-1-leitao@debian.org/
I can include this in v2 if needed.
What do you think ?
---8<---
diff --git a/net/core/sock.c b/net/core/sock.c
index 9370fd50aa2c..f1e887c3115f 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1815,14 +1815,14 @@ int sk_getsockopt(struct sock *sk, int level, int optname,
case SO_PEERNAME:
{
- char address[128];
+ struct sockaddr_storage address;
- lv = sock->ops->getname(sock, (struct sockaddr *)address, 2);
+ lv = sock->ops->getname(sock, (struct sockaddr *)&address, 2);
if (lv < 0)
return -ENOTCONN;
if (lv < len)
return -EINVAL;
- if (copy_to_sockptr(optval, address, len))
+ if (copy_to_sockptr(optval, &address, len))
return -EFAULT;
goto lenout;
}
---8<---
Thanks!
>
> >
> > To avoid the warning, we need to let __fortify_memcpy_chk() know the
> > actual buffer size.
> >
> > Another option would be to use strncpy() and limit the copied length
> > to sizeof(sll_addr), but it will return the partial address and might
> > break an application that passes sockaddr_storage to getsockname().
>
> Yeah, that would break stuff.
>
> > [0]:
> > memcpy: detected field-spanning write (size 16) of single field "sll->sll_addr" at net/packet/af_packet.c:3604 (size 8)
> > WARNING: CPU: 0 PID: 255 at net/packet/af_packet.c:3604 packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604
> > Modules linked in:
> > CPU: 0 PID: 255 Comm: syz-executor750 Not tainted 6.5.0-rc1-00330-g60cc1f7d0605 #4
> > Hardware name: linux,dummy-virt (DT)
> > pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> > pc : packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604
> > lr : packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604
> > sp : ffff800089887bc0
> > x29: ffff800089887bc0 x28: ffff000010f80f80 x27: 0000000000000003
> > x26: dfff800000000000 x25: ffff700011310f80 x24: ffff800087d55000
> > x23: dfff800000000000 x22: ffff800089887c2c x21: 0000000000000010
> > x20: ffff00000de08310 x19: ffff800089887c20 x18: ffff800086ab1630
> > x17: 20646c6569662065 x16: 6c676e697320666f x15: 0000000000000001
> > x14: 1fffe0000d56d7ca x13: 0000000000000000 x12: 0000000000000000
> > x11: 0000000000000000 x10: 0000000000000000 x9 : 3e60944c3da92b00
> > x8 : 3e60944c3da92b00 x7 : 0000000000000001 x6 : 0000000000000001
> > x5 : ffff8000898874f8 x4 : ffff800086ac99e0 x3 : ffff8000803f8808
> > x2 : 0000000000000001 x1 : 0000000100000000 x0 : 0000000000000000
> > Call trace:
> > packet_getname+0x25c/0x3a0 net/packet/af_packet.c:3604
> > __sys_getsockname+0x168/0x24c net/socket.c:2042
> > __do_sys_getsockname net/socket.c:2057 [inline]
> > __se_sys_getsockname net/socket.c:2054 [inline]
> > __arm64_sys_getsockname+0x7c/0x94 net/socket.c:2054
> > __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
> > invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52
> > el0_svc_common+0x134/0x240 arch/arm64/kernel/syscall.c:139
> > do_el0_svc+0x64/0x198 arch/arm64/kernel/syscall.c:188
> > el0_svc+0x2c/0x7c arch/arm64/kernel/entry-common.c:647
> > el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:665
> > el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:591
> >
> > Fixes: df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3")
> > Reported-by: syzkaller <syzkaller@...glegroups.com>
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> > ---
> > net/packet/af_packet.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> > index 85ff90a03b0c..5eef94a32a4f 100644
> > --- a/net/packet/af_packet.c
> > +++ b/net/packet/af_packet.c
> > @@ -3601,7 +3601,10 @@ static int packet_getname(struct socket *sock, struct sockaddr *uaddr,
> > if (dev) {
> > sll->sll_hatype = dev->type;
> > sll->sll_halen = dev->addr_len;
> > - memcpy(sll->sll_addr, dev->dev_addr, dev->addr_len);
> > +
> > + /* Let __fortify_memcpy_chk() know the actual buffer size. */
> > + memcpy(((struct sockaddr_storage *)sll)->__data +
> > + offsetof(struct sockaddr_ll, sll_addr), dev->dev_addr, dev->addr_len);
> > } else {
> > sll->sll_hatype = 0; /* Bad: we have no ARPHRD_UNSPEC */
> > sll->sll_halen = 0;
> > --
> > 2.30.2
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