2023-08-08 23:14:50

by Justin Stitt

Subject: [PATCH 1/7] netfilter: ipset: refactor deprecated strncpy

Fixes several buffer overread bugs present in `ip_set_core.c` by using
`strscpy` over `strncpy`.

Link: https://github.com/KSPP/linux/issues/90
Cc: [email protected]
Signed-off-by: Justin Stitt <[email protected]>

---
There exists several potential buffer overread bugs here. These bugs
exist due to the fact that the destination and source strings may have
the same length which is equal to the max length `IPSET_MAXNAMELEN`.

Here's an example:
| #define MAXLEN 5
| char dest[MAXLEN];
| const char *src = "hello";
| strncpy(dest, src, MAXLEN); // -> should use strscpy()
| // dest is now not NUL-terminated

Note:
This patch means that truncation now happens silently (which is better
than a silent bug) but perhaps we should have some assertions that
fail when a truncation is imminent. Thoughts?
---
net/netfilter/ipset/ip_set_core.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 0b68e2e2824e..fc77080d41a2 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -872,7 +872,7 @@ ip_set_name_byindex(struct net *net, ip_set_id_t index, char *name)
BUG_ON(!set);

read_lock_bh(&ip_set_ref_lock);
- strncpy(name, set->name, IPSET_MAXNAMELEN);
+ strscpy(name, set->name, IPSET_MAXNAMELEN);
read_unlock_bh(&ip_set_ref_lock);
}
EXPORT_SYMBOL_GPL(ip_set_name_byindex);
@@ -1326,7 +1326,7 @@ static int ip_set_rename(struct sk_buff *skb, const struct nfnl_info *info,
goto out;
}
}
- strncpy(set->name, name2, IPSET_MAXNAMELEN);
+ strscpy(set->name, name2, IPSET_MAXNAMELEN);

out:
write_unlock_bh(&ip_set_ref_lock);
@@ -1380,9 +1380,9 @@ static int ip_set_swap(struct sk_buff *skb, const struct nfnl_info *info,
return -EBUSY;
}

- strncpy(from_name, from->name, IPSET_MAXNAMELEN);
- strncpy(from->name, to->name, IPSET_MAXNAMELEN);
- strncpy(to->name, from_name, IPSET_MAXNAMELEN);
+ strscpy(from_name, from->name, IPSET_MAXNAMELEN);
+ strscpy(from->name, to->name, IPSET_MAXNAMELEN);
+ strscpy(to->name, from_name, IPSET_MAXNAMELEN);

swap(from->ref, to->ref);
ip_set(inst, from_id) = to;

--
2.41.0.640.ga95def55d0-goog

2023-08-09 01:32:10

by Florian Westphal

Subject: Re: [PATCH 1/7] netfilter: ipset: refactor deprecated strncpy

Justin Stitt <[email protected]> wrote:
> Fixes several buffer overread bugs present in `ip_set_core.c` by using
> `strscpy` over `strncpy`.
>
> Link: https://github.com/KSPP/linux/issues/90
> Cc: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>
>
> ---
> There exists several potential buffer overread bugs here. These bugs
> exist due to the fact that the destination and source strings may have
> the same length which is equal to the max length `IPSET_MAXNAMELEN`.

There is no truncation. Inputs are checked via nla_policy:

[IPSET_ATTR_SETNAME2] = { .type = NLA_NUL_STRING, .len = IPSET_MAXNAMELEN - 1 },

2023-08-09 06:39:58

by Kees Cook

Subject: Re: [PATCH 1/7] netfilter: ipset: refactor deprecated strncpy

On Wed, Aug 09, 2023 at 01:38:55AM +0200, Florian Westphal wrote:
> Justin Stitt <[email protected]> wrote:
> > Fixes several buffer overread bugs present in `ip_set_core.c` by using
> > `strscpy` over `strncpy`.
> >
> > Link: https://github.com/KSPP/linux/issues/90
> > Cc: [email protected]
> > Signed-off-by: Justin Stitt <[email protected]>
> >
> > ---
> > There exists several potential buffer overread bugs here. These bugs
> > exist due to the fact that the destination and source strings may have
> > the same length which is equal to the max length `IPSET_MAXNAMELEN`.
>
> There is no truncation. Inputs are checked via nla_policy:
>
> [IPSET_ATTR_SETNAME2] = { .type = NLA_NUL_STRING, .len = IPSET_MAXNAMELEN - 1 },

Ah, perfect. Yeah, so if it needs to zero-padding, but it is always
NUL-terminated, strscpy_pad() is the right replacement. Thanks!

--
Kees Cook