* Re: [PATCH 12/26] netfilter: switch nf_setsockopt to sockptr_t
[not found] ` <20200727150601.GA3447@lst.de>
@ 2020-07-27 16:16 ` Jason A. Donenfeld
2020-07-27 16:23 ` Christoph Hellwig
0 siblings, 1 reply; 4+ messages in thread
From: Jason A. Donenfeld @ 2020-07-27 16:16 UTC (permalink / raw)
To: Christoph Hellwig
Cc: David S. Miller, Jakub Kicinski, Alexei Starovoitov,
Daniel Borkmann, Alexey Kuznetsov, Hideaki YOSHIFUJI,
Eric Dumazet, Linux Crypto Mailing List, LKML, Netdev, bpf,
netfilter-devel, coreteam, linux-sctp, linux-hams,
linux-bluetooth, bridge, linux-can, dccp, linux-decnet-user,
linux-wpan, linux-s390, mptcp, lvs-devel, rds-devel, linux-afs,
tipc-discussion, linux-x25, Kernel Hardening
On Mon, Jul 27, 2020 at 5:06 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Mon, Jul 27, 2020 at 05:03:10PM +0200, Jason A. Donenfeld wrote:
> > Hi Christoph,
> >
> > On Thu, Jul 23, 2020 at 08:08:54AM +0200, Christoph Hellwig wrote:
> > > diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
> > > index da933f99b5d517..42befbf12846c0 100644
> > > --- a/net/ipv4/ip_sockglue.c
> > > +++ b/net/ipv4/ip_sockglue.c
> > > @@ -1422,7 +1422,8 @@ int ip_setsockopt(struct sock *sk, int level,
> > > optname != IP_IPSEC_POLICY &&
> > > optname != IP_XFRM_POLICY &&
> > > !ip_mroute_opt(optname))
> > > - err = nf_setsockopt(sk, PF_INET, optname, optval, optlen);
> > > + err = nf_setsockopt(sk, PF_INET, optname, USER_SOCKPTR(optval),
> > > + optlen);
> > > #endif
> > > return err;
> > > }
> > > diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
> > > index 4697d09c98dc3e..f2a9680303d8c0 100644
> > > --- a/net/ipv4/netfilter/ip_tables.c
> > > +++ b/net/ipv4/netfilter/ip_tables.c
> > > @@ -1102,7 +1102,7 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks,
> > > }
> > >
> > > static int
> > > -do_replace(struct net *net, const void __user *user, unsigned int len)
> > > +do_replace(struct net *net, sockptr_t arg, unsigned int len)
> > > {
> > > int ret;
> > > struct ipt_replace tmp;
> > > @@ -1110,7 +1110,7 @@ do_replace(struct net *net, const void __user *user, unsigned int len)
> > > void *loc_cpu_entry;
> > > struct ipt_entry *iter;
> > >
> > > - if (copy_from_user(&tmp, user, sizeof(tmp)) != 0)
> > > + if (copy_from_sockptr(&tmp, arg, sizeof(tmp)) != 0)
> > > return -EFAULT;
> > >
> > > /* overflow check */
> > > @@ -1126,8 +1126,8 @@ do_replace(struct net *net, const void __user *user, unsigned int len)
> > > return -ENOMEM;
> > >
> > > loc_cpu_entry = newinfo->entries;
> > > - if (copy_from_user(loc_cpu_entry, user + sizeof(tmp),
> > > - tmp.size) != 0) {
> > > + sockptr_advance(arg, sizeof(tmp));
> > > + if (copy_from_sockptr(loc_cpu_entry, arg, tmp.size) != 0) {
> > > ret = -EFAULT;
> > > goto free_newinfo;
> > > }
> >
> > Something along this path seems to have broken with this patch. An
> > invocation of `iptables -A INPUT -m length --length 1360 -j DROP` now
> > fails, with
> >
> > nf_setsockopt->do_replace->translate_table->check_entry_size_and_hooks:
> > (unsigned char *)e + e->next_offset > limit ==> TRUE
> >
> > resulting in the whole call chain returning -EINVAL. It bisects back to
> > this commit. This is on net-next.
>
> This is another use o sockptr_advance that Ido already found a problem
> in. I'm looking into this at the moment..
I haven't seen Ido's patch, but it seems clear the issue is that you
want to call `sockptr_advance(&arg, sizeof(tmp))`, and adjust
sockptr_advance to take a pointer.
Slight concern about the whole concept:
Things are defined as
typedef union {
void *kernel;
void __user *user;
} sockptr_t;
static inline bool sockptr_is_kernel(sockptr_t sockptr)
{
return (unsigned long)sockptr.kernel >= TASK_SIZE;
}
So what happens if we have some code like:
sockptr_t sp;
init_user_sockptr(&sp, user_controlled_struct.extra_user_ptr);
sockptr_advance(&sp, user_controlled_struct.some_big_offset);
copy_to_sockptr(&sp, user_controlled_struct.a_few_bytes,
sizeof(user_controlled_struct.a_few_bytes));
With the user controlling some_big_offset, he can convert the user
sockptr into a kernel sockptr, causing the subsequent copy_to_sockptr
to be a vanilla memcpy, after which a security disaster ensues.
Maybe sockptr_advance should have some safety checks and sometimes
return -EFAULT? Or you should always use the implementation where
being a kernel address is an explicit bit of sockptr_t, rather than
being implicit?
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 12/26] netfilter: switch nf_setsockopt to sockptr_t
2020-07-27 16:16 ` [PATCH 12/26] netfilter: switch nf_setsockopt to sockptr_t Jason A. Donenfeld
@ 2020-07-27 16:23 ` Christoph Hellwig
2020-07-28 8:07 ` David Laight
0 siblings, 1 reply; 4+ messages in thread
From: Christoph Hellwig @ 2020-07-27 16:23 UTC (permalink / raw)
To: Jason A. Donenfeld
Cc: Christoph Hellwig, David S. Miller, Jakub Kicinski,
Alexei Starovoitov, Daniel Borkmann, Alexey Kuznetsov,
Hideaki YOSHIFUJI, Eric Dumazet, Linux Crypto Mailing List, LKML,
Netdev, bpf, netfilter-devel, coreteam, linux-sctp, linux-hams,
linux-bluetooth, bridge, linux-can, dccp, linux-decnet-user,
linux-wpan, linux-s390, mptcp, lvs-devel, rds-devel, linux-afs,
tipc-discussion, linux-x25, Kernel Hardening
On Mon, Jul 27, 2020 at 06:16:32PM +0200, Jason A. Donenfeld wrote:
> Maybe sockptr_advance should have some safety checks and sometimes
> return -EFAULT? Or you should always use the implementation where
> being a kernel address is an explicit bit of sockptr_t, rather than
> being implicit?
I already have a patch to use access_ok to check the whole range in
init_user_sockptr.
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [PATCH 12/26] netfilter: switch nf_setsockopt to sockptr_t
2020-07-27 16:23 ` Christoph Hellwig
@ 2020-07-28 8:07 ` David Laight
2020-07-28 8:17 ` Jason A. Donenfeld
0 siblings, 1 reply; 4+ messages in thread
From: David Laight @ 2020-07-28 8:07 UTC (permalink / raw)
To: 'Christoph Hellwig', Jason A. Donenfeld
Cc: David S. Miller, Jakub Kicinski, Alexei Starovoitov,
Daniel Borkmann, Alexey Kuznetsov, Hideaki YOSHIFUJI,
Eric Dumazet, Linux Crypto Mailing List, LKML, Netdev, bpf,
netfilter-devel, coreteam, linux-sctp, linux-hams,
linux-bluetooth, bridge, linux-can, dccp, linux-decnet-user,
linux-wpan, linux-s390, mptcp, lvs-devel, rds-devel, linux-afs,
tipc-discussion, linux-x25, Kernel Hardening
From: Christoph Hellwig
> Sent: 27 July 2020 17:24
>
> On Mon, Jul 27, 2020 at 06:16:32PM +0200, Jason A. Donenfeld wrote:
> > Maybe sockptr_advance should have some safety checks and sometimes
> > return -EFAULT? Or you should always use the implementation where
> > being a kernel address is an explicit bit of sockptr_t, rather than
> > being implicit?
>
> I already have a patch to use access_ok to check the whole range in
> init_user_sockptr.
That doesn't make (much) difference to the code paths that ignore
the user-supplied length.
OTOH doing the user/kernel check on the base address (not an
incremented one) means that the correct copy function is always
selected.
Perhaps the functions should all be passed a 'const sockptr_t'.
The typedef could be made 'const' - requiring non-const items
explicitly use the union/struct itself.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 12/26] netfilter: switch nf_setsockopt to sockptr_t
2020-07-28 8:07 ` David Laight
@ 2020-07-28 8:17 ` Jason A. Donenfeld
0 siblings, 0 replies; 4+ messages in thread
From: Jason A. Donenfeld @ 2020-07-28 8:17 UTC (permalink / raw)
To: David Laight
Cc: Christoph Hellwig, David S. Miller, Jakub Kicinski,
Alexei Starovoitov, Daniel Borkmann, Alexey Kuznetsov,
Hideaki YOSHIFUJI, Eric Dumazet, Linux Crypto Mailing List, LKML,
Netdev, bpf, netfilter-devel, coreteam, linux-sctp, linux-hams,
linux-bluetooth, bridge, linux-can, dccp, linux-decnet-user,
linux-wpan, linux-s390, mptcp, lvs-devel, rds-devel, linux-afs,
tipc-discussion, linux-x25, Kernel Hardening
On Tue, Jul 28, 2020 at 10:07 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: Christoph Hellwig
> > Sent: 27 July 2020 17:24
> >
> > On Mon, Jul 27, 2020 at 06:16:32PM +0200, Jason A. Donenfeld wrote:
> > > Maybe sockptr_advance should have some safety checks and sometimes
> > > return -EFAULT? Or you should always use the implementation where
> > > being a kernel address is an explicit bit of sockptr_t, rather than
> > > being implicit?
> >
> > I already have a patch to use access_ok to check the whole range in
> > init_user_sockptr.
>
> That doesn't make (much) difference to the code paths that ignore
> the user-supplied length.
> OTOH doing the user/kernel check on the base address (not an
> incremented one) means that the correct copy function is always
> selected.
Right, I had the same reaction in reading this, but actually, his code
gets rid of the sockptr_advance stuff entirely and never mutates, so
even though my point about attacking those pointers was missed, the
code does the better thing now -- checking the base address and never
mutating the pointer. So I think we're good.
>
> Perhaps the functions should all be passed a 'const sockptr_t'.
> The typedef could be made 'const' - requiring non-const items
> explicitly use the union/struct itself.
I was thinking the same, but just by making the pointers inside the
struct const. However, making the whole struct const via the typedef
is a much better idea. That'd probably require changing the signature
of init_user_sockptr a bit, which would be fine, but indeed I think
this would be a very positive change.
Jason
^ permalink raw reply [flat|nested] 4+ messages in thread
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[not found] ` <20200727150601.GA3447@lst.de>
2020-07-27 16:16 ` [PATCH 12/26] netfilter: switch nf_setsockopt to sockptr_t Jason A. Donenfeld
2020-07-27 16:23 ` Christoph Hellwig
2020-07-28 8:07 ` David Laight
2020-07-28 8:17 ` Jason A. Donenfeld
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