[PATCH net] netfilter: xt_hashlimit: do not allow empty names

[PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

Syzbot reported a WARN() in proc_create_data() [1]

Issue here is that xt_hashlimit does not check that user space provided
an empty table name.

[1]
name len 0
WARNING: CPU: 0 PID: 3680 at fs/proc/generic.c:354 __proc_create+0x696/0x880 fs/proc/generic.c:354
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 3680 Comm: syzkaller464755 Not tainted 4.15.0-rc9+ #283
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 panic+0x1e4/0x41c kernel/panic.c:183
 __warn+0x1dc/0x200 kernel/panic.c:547
 report_bug+0x211/0x2d0 lib/bug.c:184
 fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
 fixup_bug arch/x86/kernel/traps.c:247 [inline]
 do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
 invalid_op+0x22/0x40 arch/x86/entry/entry_64.S:1096
RIP: 0010:__proc_create+0x696/0x880 fs/proc/generic.c:354
RSP: 0018:ffff8801d9607410 EFLAGS: 00010286
RAX: dffffc0000000008 RBX: 1ffff1003b2c0e87 RCX: ffffffff8159ebae
RDX: 0000000000000000 RSI: 1ffff1003b284970 RDI: 0000000000000293
RBP: ffff8801d9607580 R08: 1ffff1003b2c0e15 R09: 0000000000000000
R10: ffff8801d96072c8 R11: 0000000000000000 R12: ffff8801d981ef28
R13: ffff8801d9607558 R14: 0000000000000000 R15: ffff8801d9607518
 proc_create_data+0x76/0x180 fs/proc/generic.c:488
 htable_create net/netfilter/xt_hashlimit.c:333 [inline]
 hashlimit_mt_check_common.isra.9+0xaee/0x1420 net/netfilter/xt_hashlimit.c:900
 hashlimit_mt_check_v1+0x48d/0x640 net/netfilter/xt_hashlimit.c:926
 xt_check_match+0x231/0x7d0 net/netfilter/x_tables.c:465
 check_match net/ipv4/netfilter/ip_tables.c:479 [inline]
 find_check_match net/ipv4/netfilter/ip_tables.c:495 [inline]
 find_check_entry.isra.8+0x3fc/0xcb0 net/ipv4/netfilter/ip_tables.c:544
 translate_table+0xed1/0x1610 net/ipv4/netfilter/ip_tables.c:730
 do_replace net/ipv4/netfilter/ip_tables.c:1148 [inline]
 do_ipt_set_ctl+0x370/0x5f0 net/ipv4/netfilter/ip_tables.c:1682
 nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
 nf_setsockopt+0x67/0xc0 net/netfilter/nf_sockopt.c:115
 ip_setsockopt+0xa1/0xb0 net/ipv4/ip_sockglue.c:1256
 tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2875
 sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2968
 SYSC_setsockopt net/socket.c:1831 [inline]
 SyS_setsockopt+0x189/0x360 net/socket.c:1810
 entry_SYSCALL_64_fastpath+0x29/0xa0

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
---
 net/netfilter/xt_hashlimit.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 5da8746f7b88ff4c9446f256e542e823a6a561b0..eae732e013df92a364b500645360d4606c283a75 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -894,6 +894,8 @@ static int hashlimit_mt_check_common(const struct xt_mtchk_param *par,
 			return -ERANGE;
 	}
 
+	if (!name[0])
+		return -EINVAL;
 	mutex_lock(&hashlimit_mutex);
 	*hinfo = htable_find_get(net, name, par->family);
 	if (*hinfo == NULL) {

Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Eric Dumazet]

On Sun, 2018-01-28 at 07:41 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Syzbot reported a WARN() in proc_create_data() [1]
> 
> Issue here is that xt_hashlimit does not check that user space provided
> an empty table name.

> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: syzbot <syzkaller@googlegroups.com>
> ---
>  net/netfilter/xt_hashlimit.c |    2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
> index 5da8746f7b88ff4c9446f256e542e823a6a561b0..eae732e013df92a364b500645360d4606c283a75 100644
> --- a/net/netfilter/xt_hashlimit.c
> +++ b/net/netfilter/xt_hashlimit.c
> @@ -894,6 +894,8 @@ static int hashlimit_mt_check_common(const struct xt_mtchk_param *par,
>  			return -ERANGE;
>  	}
>  
> +	if (!name[0])
> +		return -EINVAL;
>  	mutex_lock(&hashlimit_mutex);
>  	*hinfo = htable_find_get(net, name, par->family);
>  	if (*hinfo == NULL) {

I wonder if we should also check if name includes a '/' ?

if (!name[0] || strchr(name, '/'))
    return -EINVAL;

Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Florian Westphal]

Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Sun, 2018-01-28 at 07:41 -0800, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@google.com>
> > 
> > Syzbot reported a WARN() in proc_create_data() [1]
> > 
> > Issue here is that xt_hashlimit does not check that user space provided
> > an empty table name.
> 
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > Reported-by: syzbot <syzkaller@googlegroups.com>
> > ---
> >  net/netfilter/xt_hashlimit.c |    2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
> > index 5da8746f7b88ff4c9446f256e542e823a6a561b0..eae732e013df92a364b500645360d4606c283a75 100644
> > --- a/net/netfilter/xt_hashlimit.c
> > +++ b/net/netfilter/xt_hashlimit.c
> > @@ -894,6 +894,8 @@ static int hashlimit_mt_check_common(const struct xt_mtchk_param *par,
> >  			return -ERANGE;
> >  	}
> >  
> > +	if (!name[0])
> > +		return -EINVAL;
> >  	mutex_lock(&hashlimit_mutex);
> >  	*hinfo = htable_find_get(net, name, par->family);
> >  	if (*hinfo == NULL) {
> 
> I wonder if we should also check if name includes a '/' ?
> 
> if (!name[0] || strchr(name, '/'))
>     return -EINVAL;

I think there should be a helper for this to reject

- 0 length
- /
- .
- ..

in hashlimit case name is IFNMASIZ so we could even use
dev_valid_name() here.

Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Pablo Neira Ayuso]

On Sun, Jan 28, 2018 at 09:54:05AM -0800, Eric Dumazet wrote:
> On Sun, 2018-01-28 at 07:41 -0800, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@google.com>
> > 
> > Syzbot reported a WARN() in proc_create_data() [1]
> > 
> > Issue here is that xt_hashlimit does not check that user space provided
> > an empty table name.
> 
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > Reported-by: syzbot <syzkaller@googlegroups.com>
> > ---
> >  net/netfilter/xt_hashlimit.c |    2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
> > index 5da8746f7b88ff4c9446f256e542e823a6a561b0..eae732e013df92a364b500645360d4606c283a75 100644
> > --- a/net/netfilter/xt_hashlimit.c
> > +++ b/net/netfilter/xt_hashlimit.c
> > @@ -894,6 +894,8 @@ static int hashlimit_mt_check_common(const struct xt_mtchk_param *par,
> >  			return -ERANGE;
> >  	}
> >  
> > +	if (!name[0])
> > +		return -EINVAL;
> >  	mutex_lock(&hashlimit_mutex);
> >  	*hinfo = htable_find_get(net, name, par->family);
> >  	if (*hinfo == NULL) {
> 
> I wonder if we should also check if name includes a '/' ?
> 
> if (!name[0] || strchr(name, '/'))
>     return -EINVAL;

We can probably add our own variant of dev_valid_name?

bool nf_valid_name(const char *name, size_t len)
{
        if (*name == '\0')
                return false;
        if (strlen(name) >= len)
                return false;
        if (!strcmp(name, ".") || !strcmp(name, ".."))
                return false;

        while (*name) {
                if (*name == '/' || *name == ':' || isspace(*name))
                        return false;
                name++;
        }
        return true;
}

Or place this in the core, something like:

bool net_valid_name(const char *name, size_t len)
{
        ...
}

then use it from dev_valid_name()

bool dev_valid_name(const char *name)
{
        return net_valid_name(name, IFNAMSIZ);
}

@Eric, I can give it a shot here to this, just let me know. Thanks!

Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Pablo Neira Ayuso]

On Fri, Feb 02, 2018 at 12:49:38PM +0100, Pablo Neira Ayuso wrote:
[...]
> 
> Or place this in the core, something like:
> 
> bool net_valid_name(const char *name, size_t len)
> {
>         ...
> }
> 
> then use it from dev_valid_name()
> 
> bool dev_valid_name(const char *name)
> {
>         return net_valid_name(name, IFNAMSIZ);
> }

Just to clarify, I think I prefer this approach, probably other
subsystem can benefit from this generic approach too.

BTW, I wonder if we should use strnlen() instead of strlen() in
dev_valid_name(), I guess this not useful for device name since they
are guaranteed to be nul-terminated, but netfilter this would be good
given userspace can send us a non nul-terminated string. But in
general, I think it doesn't harm to use strnlen() in dev_valid_name().

Am I missing anything in all these tricky string handling? Thanks!

Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Pablo Neira Ayuso]

On Fri, Feb 02, 2018 at 12:55:22PM +0100, Pablo Neira Ayuso wrote:
> On Fri, Feb 02, 2018 at 12:49:38PM +0100, Pablo Neira Ayuso wrote:
> [...]
> > 
> > Or place this in the core, something like:
> > 
> > bool net_valid_name(const char *name, size_t len)
> > {
> >         ...
> > }
> > 
> > then use it from dev_valid_name()
> > 
> > bool dev_valid_name(const char *name)
> > {
> >         return net_valid_name(name, IFNAMSIZ);
> > }
> 
> Just to clarify, I think I prefer this approach, probably other
> subsystem can benefit from this generic approach too.
> 
> BTW, I wonder if we should use strnlen() instead of strlen() in
> dev_valid_name(), I guess this not useful for device name since they
> are guaranteed to be nul-terminated, but netfilter this would be good
> given userspace can send us a non nul-terminated string. But in
> general, I think it doesn't harm to use strnlen() in dev_valid_name().

Argh sorry, I'm talking about the hypothetical net_valid_name()
function, not dev_valid_name() itself.

Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Jan Engelhardt]

On Friday 2018-02-02 12:55, Pablo Neira Ayuso wrote:

>On Fri, Feb 02, 2018 at 12:49:38PM +0100, Pablo Neira Ayuso wrote:
>[...]
>> bool net_valid_name(const char *name, size_t len)
>> {
>>         ...
>> }
>
>Am I missing anything in all these tricky string handling? Thanks!

One will have to watch out for calls like

	net_valid_name(NLA_DATA(some_ifla_name), IFNAMSIZ)

because quite some nlattrs (IFLA_NAME, IFLA_IFNAME to boot) are NLA_STRINGs
(rather than NLA_NUL_STRINGs) and they are not \0-terminated.

Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Pablo Neira Ayuso]

On Fri, Feb 02, 2018 at 01:12:08PM +0100, Jan Engelhardt wrote:
> On Friday 2018-02-02 12:55, Pablo Neira Ayuso wrote:
> 
> >On Fri, Feb 02, 2018 at 12:49:38PM +0100, Pablo Neira Ayuso wrote:
> >[...]
> >> bool net_valid_name(const char *name, size_t len)
> >> {
> >>         ...
> >> }
> >
> >Am I missing anything in all these tricky string handling? Thanks!
> 
> One will have to watch out for calls like
> 
> 	net_valid_name(NLA_DATA(some_ifla_name), IFNAMSIZ)
> 
> because quite some nlattrs (IFLA_NAME, IFLA_IFNAME to boot) are NLA_STRINGs
> (rather than NLA_NUL_STRINGs) and they are not \0-terminated.

As long as we use nla_str*() helpers, we're all good.

Re: [PATCH net] netfilter: xt_hashlimit: do not allow empty names

[Eric Dumazet]

On Fri, 2018-02-02 at 12:49 +0100, Pablo Neira Ayuso wrote:

> @Eric, I can give it a shot here to this, just let me know. Thanks!

Please go ahead Pablo !

Thanks.