[PATCH v2 0/7] netfilter: refactor deprecated strncpy

[PATCH v2 0/7] netfilter: refactor deprecated strncpy

[Justin Stitt]

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

A suitable replacement is `strscpy` or `strscpy_pad` [2] due to the fact
that they guarantee NUL-termination on their destination buffer argument
which is _not_ the case for `strncpy`!

This series of patches aims to swap out `strncpy` for more a robust and
less ambiguous interface `strscpy_pad` . This patch series, if applied
in its entirety, removes most if not all instances of `strncpy` in the
`net/netfilter` directory.

[1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
[2]: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html

Link: https://github.com/KSPP/linux/issues/90
Related: commit 8556bceb9c40 ("netfilter: move from strlcpy with unused retval to strscpy")
---
Changes in v2:
- use `strscpy_pad` instead of `strscpy` since zero-padding is needed
  (thanks Florian and Kees)
- Link to v1: https://lore.kernel.org/r/20230808-net-netfilter-v1-0-efbbe4ec60af@google.com

---
Justin Stitt (7):
      netfilter: ipset: refactor deprecated strncpy
      netfilter: nf_tables: refactor deprecated strncpy
      netfilter: nf_tables: refactor deprecated strncpy
      netfilter: nft_meta: refactor deprecated strncpy
      netfilter: nft_osf: refactor deprecated strncpy
      netfilter: x_tables: refactor deprecated strncpy
      netfilter: xtables: refactor deprecated strncpy

 net/netfilter/ipset/ip_set_core.c | 10 +++++-----
 net/netfilter/nft_ct.c            |  2 +-
 net/netfilter/nft_fib.c           |  2 +-
 net/netfilter/nft_meta.c          |  6 +++---
 net/netfilter/nft_osf.c           |  6 +++---
 net/netfilter/x_tables.c          |  5 ++---
 net/netfilter/xt_repldata.h       |  2 +-
 7 files changed, 16 insertions(+), 17 deletions(-)
---
base-commit: 14f9643dc90adea074a0ffb7a17d337eafc6a5cc
change-id: 20230807-net-netfilter-4027219bb6e7

Best regards,
--
Justin Stitt <justinstitt@google.com>

[PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

[Justin Stitt]

Use `strscpy_pad` instead of `strncpy`.

Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 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..e564b5174261 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_pad(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_pad(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_pad(from_name, from->name, IPSET_MAXNAMELEN);
+	strscpy_pad(from->name, to->name, IPSET_MAXNAMELEN);
+	strscpy_pad(to->name, from_name, IPSET_MAXNAMELEN);
 
 	swap(from->ref, to->ref);
 	ip_set(inst, from_id) = to;

-- 
2.41.0.640.ga95def55d0-goog

Re: [PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

[Florian Westphal]

Justin Stitt <justinstitt@google.com> wrote:
> Use `strscpy_pad` instead of `strncpy`.

I don't think that any of these need zero-padding.

Re: [PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

[Justin Stitt]

On Wed, Aug 9, 2023 at 1:19 PM Florian Westphal <fw@strlen.de> wrote:
>
> Justin Stitt <justinstitt@google.com> wrote:
> > Use `strscpy_pad` instead of `strncpy`.
>
> I don't think that any of these need zero-padding.
It's a more consistent change with the rest of the series and I don't
believe it has much different behavior to `strncpy` (other than
NUL-termination) as that will continue to pad to `n` as well.

Do you think the `_pad` for 1/7, 6/7 and 7/7 should be changed back to
`strscpy` in a v3? I really am shooting in the dark as it is quite
hard to tell whether or not a buffer is expected to be NUL-padded or
not.

Re: [PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

[Jan Engelhardt]

On Wednesday 2023-08-09 23:40, Justin Stitt wrote:
>On Wed, Aug 9, 2023 at 1:19 PM Florian Westphal <fw@strlen.de> wrote:
>>
>> Justin Stitt <justinstitt@google.com> wrote:
>> > Use `strscpy_pad` instead of `strncpy`.
>>
>> I don't think that any of these need zero-padding.
>It's a more consistent change with the rest of the series and I don't
>believe it has much different behavior to `strncpy` (other than
>NUL-termination) as that will continue to pad to `n` as well.
>
>Do you think the `_pad` for 1/7, 6/7 and 7/7 should be changed back to
>`strscpy` in a v3? I really am shooting in the dark as it is quite
>hard to tell whether or not a buffer is expected to be NUL-padded or
>not.

I don't recall either NF userspace or kernelspace code doing memcmp
with name-like fields, so padding should not be strictly needed.

Re: [PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

[Kees Cook]

On Wed, Aug 09, 2023 at 11:54:48PM +0200, Jan Engelhardt wrote:
> 
> On Wednesday 2023-08-09 23:40, Justin Stitt wrote:
> >On Wed, Aug 9, 2023 at 1:19 PM Florian Westphal <fw@strlen.de> wrote:
> >>
> >> Justin Stitt <justinstitt@google.com> wrote:
> >> > Use `strscpy_pad` instead of `strncpy`.
> >>
> >> I don't think that any of these need zero-padding.
> >It's a more consistent change with the rest of the series and I don't
> >believe it has much different behavior to `strncpy` (other than
> >NUL-termination) as that will continue to pad to `n` as well.
> >
> >Do you think the `_pad` for 1/7, 6/7 and 7/7 should be changed back to
> >`strscpy` in a v3? I really am shooting in the dark as it is quite
> >hard to tell whether or not a buffer is expected to be NUL-padded or
> >not.
> 
> I don't recall either NF userspace or kernelspace code doing memcmp
> with name-like fields, so padding should not be strictly needed.

My only concern with padding is just to make sure any buffers copied to
userspace have been zeroed. I would need to take a close look at how
buffers are passed around here to know for sure...

-- 
Kees Cook

Re: [PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

[Florian Westphal]

Justin Stitt <justinstitt@google.com> wrote:
> On Wed, Aug 9, 2023 at 1:19 PM Florian Westphal <fw@strlen.de> wrote:
> >
> > Justin Stitt <justinstitt@google.com> wrote:
> > > Use `strscpy_pad` instead of `strncpy`.
> >
> > I don't think that any of these need zero-padding.
> It's a more consistent change with the rest of the series and I don't
> believe it has much different behavior to `strncpy` (other than
> NUL-termination) as that will continue to pad to `n` as well.
> 
> Do you think the `_pad` for 1/7, 6/7 and 7/7 should be changed back to
> `strscpy` in a v3? I really am shooting in the dark as it is quite
> hard to tell whether or not a buffer is expected to be NUL-padded or
> not.

No, you can keep it as-is.  Which tree are you targetting with this?

Re: [PATCH v2 1/7] netfilter: ipset: refactor deprecated strncpy

[Justin Stitt]

On Wed, Aug 9, 2023 at 2:58 PM Florian Westphal <fw@strlen.de> wrote:
>
> Justin Stitt <justinstitt@google.com> wrote:
> > On Wed, Aug 9, 2023 at 1:19 PM Florian Westphal <fw@strlen.de> wrote:
> > >
> > > Justin Stitt <justinstitt@google.com> wrote:
> > > > Use `strscpy_pad` instead of `strncpy`.
> > >
> > > I don't think that any of these need zero-padding.
> > It's a more consistent change with the rest of the series and I don't
> > believe it has much different behavior to `strncpy` (other than
> > NUL-termination) as that will continue to pad to `n` as well.
> >
> > Do you think the `_pad` for 1/7, 6/7 and 7/7 should be changed back to
> > `strscpy` in a v3? I really am shooting in the dark as it is quite
> > hard to tell whether or not a buffer is expected to be NUL-padded or
> > not.
>
> No, you can keep it as-is.  Which tree are you targetting with this?
Not sure, I let ./getmaintainer auto-add the mailing lists. Perhaps
netdev or netfilter next trees?

[PATCH v2 2/7] netfilter: nf_tables: refactor deprecated strncpy

[Justin Stitt]

Prefer `strscpy_pad` over `strncpy`.

Signed-off-by: Justin Stitt <justinstitt@google.com>

---
Note: Opt for `strscpy_pad` over `strscpy` since padding is wanted [1]

Link: https://lore.kernel.org/all/20230808234001.GJ9741@breakpoint.cc/ [1]
---
 net/netfilter/nft_ct.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nft_ct.c b/net/netfilter/nft_ct.c
index 38958e067aa8..bbf11c4871b2 100644
--- a/net/netfilter/nft_ct.c
+++ b/net/netfilter/nft_ct.c
@@ -108,7 +108,7 @@ static void nft_ct_get_eval(const struct nft_expr *expr,
 		helper = rcu_dereference(help->helper);
 		if (helper == NULL)
 			goto err;
-		strncpy((char *)dest, helper->name, NF_CT_HELPER_NAME_LEN);
+		strscpy_pad((char *)dest, helper->name, NF_CT_HELPER_NAME_LEN);
 		return;
 #ifdef CONFIG_NF_CONNTRACK_LABELS
 	case NFT_CT_LABELS: {

-- 
2.41.0.640.ga95def55d0-goog

[PATCH v2 3/7] netfilter: nf_tables: refactor deprecated strncpy

[Justin Stitt]

Prefer `strscpy_pad` over `strncpy`.

Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 net/netfilter/nft_fib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nft_fib.c b/net/netfilter/nft_fib.c
index 6e049fd48760..8c250a47a3b4 100644
--- a/net/netfilter/nft_fib.c
+++ b/net/netfilter/nft_fib.c
@@ -150,7 +150,7 @@ void nft_fib_store_result(void *reg, const struct nft_fib *priv,
 		if (priv->flags & NFTA_FIB_F_PRESENT)
 			*dreg = !!dev;
 		else
-			strncpy(reg, dev ? dev->name : "", IFNAMSIZ);
+			strscpy_pad(reg, dev ? dev->name : "", IFNAMSIZ);
 		break;
 	default:
 		WARN_ON_ONCE(1);

-- 
2.41.0.640.ga95def55d0-goog

[PATCH v2 4/7] netfilter: nft_meta: refactor deprecated strncpy

[Justin Stitt]

Prefer `strscpy_pad` to `strncpy`.

Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 net/netfilter/nft_meta.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_meta.c b/net/netfilter/nft_meta.c
index 8fdc7318c03c..f7da7c43333b 100644
--- a/net/netfilter/nft_meta.c
+++ b/net/netfilter/nft_meta.c
@@ -185,12 +185,12 @@ static noinline bool nft_meta_get_eval_kind(enum nft_meta_keys key,
 	case NFT_META_IIFKIND:
 		if (!in || !in->rtnl_link_ops)
 			return false;
-		strncpy((char *)dest, in->rtnl_link_ops->kind, IFNAMSIZ);
+		strscpy_pad((char *)dest, in->rtnl_link_ops->kind, IFNAMSIZ);
 		break;
 	case NFT_META_OIFKIND:
 		if (!out || !out->rtnl_link_ops)
 			return false;
-		strncpy((char *)dest, out->rtnl_link_ops->kind, IFNAMSIZ);
+		strscpy_pad((char *)dest, out->rtnl_link_ops->kind, IFNAMSIZ);
 		break;
 	default:
 		return false;
@@ -206,7 +206,7 @@ static void nft_meta_store_ifindex(u32 *dest, const struct net_device *dev)
 
 static void nft_meta_store_ifname(u32 *dest, const struct net_device *dev)
 {
-	strncpy((char *)dest, dev ? dev->name : "", IFNAMSIZ);
+	strscpy_pad((char *)dest, dev ? dev->name : "", IFNAMSIZ);
 }
 
 static bool nft_meta_store_iftype(u32 *dest, const struct net_device *dev)

-- 
2.41.0.640.ga95def55d0-goog

[PATCH v2 5/7] netfilter: nft_osf: refactor deprecated strncpy

[Justin Stitt]

Use `strscpy_pad` over `strncpy` for NUL-terminated strings.

We can also drop the + 1 from `NFT_OSF_MAXGENRELEN + 1` since `strscpy`
will guarantee NUL-termination.

Signed-off-by: Justin Stitt <justinstitt@google.com>

---
Note: Should this usage @8556bceb9c409 also be changed to `strscpy_pad`
or is zero-padding not required here?
---
 net/netfilter/nft_osf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_osf.c b/net/netfilter/nft_osf.c
index 70820c66b591..7f61506e5b44 100644
--- a/net/netfilter/nft_osf.c
+++ b/net/netfilter/nft_osf.c
@@ -23,7 +23,7 @@ static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs,
 	struct nft_osf *priv = nft_expr_priv(expr);
 	u32 *dest = &regs->data[priv->dreg];
 	struct sk_buff *skb = pkt->skb;
-	char os_match[NFT_OSF_MAXGENRELEN + 1];
+	char os_match[NFT_OSF_MAXGENRELEN];
 	const struct tcphdr *tcp;
 	struct nf_osf_data data;
 	struct tcphdr _tcph;
@@ -45,7 +45,7 @@ static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs,
 	}
 
 	if (!nf_osf_find(skb, nf_osf_fingers, priv->ttl, &data)) {
-		strncpy((char *)dest, "unknown", NFT_OSF_MAXGENRELEN);
+		strscpy_pad((char *)dest, "unknown", NFT_OSF_MAXGENRELEN);
 	} else {
 		if (priv->flags & NFT_OSF_F_VERSION)
 			snprintf(os_match, NFT_OSF_MAXGENRELEN, "%s:%s",
@@ -53,7 +53,7 @@ static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs,
 		else
 			strscpy(os_match, data.genre, NFT_OSF_MAXGENRELEN);
 
-		strncpy((char *)dest, os_match, NFT_OSF_MAXGENRELEN);
+		strscpy_pad((char *)dest, os_match, NFT_OSF_MAXGENRELEN);
 	}
 }
 

-- 
2.41.0.640.ga95def55d0-goog

Re: [PATCH v2 5/7] netfilter: nft_osf: refactor deprecated strncpy

[Florian Westphal]

Justin Stitt <justinstitt@google.com> wrote:
 ---
> Note: Should this usage @8556bceb9c409 also be changed to `strscpy_pad`
> or is zero-padding not required here?

That commit converted strlcpy which doesn't do any zero-padding,
I don't see anything wrong with that change.

[PATCH v2 6/7] netfilter: x_tables: refactor deprecated strncpy

[Justin Stitt]

Prefer `strscpy_pad` to `strncpy`.

Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 net/netfilter/x_tables.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 470282cf3fae..21624d68314f 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -768,7 +768,7 @@ void xt_compat_match_from_user(struct xt_entry_match *m, void **dstptr,
 	m->u.user.match_size = msize;
 	strscpy(name, match->name, sizeof(name));
 	module_put(match->me);
-	strncpy(m->u.user.name, name, sizeof(m->u.user.name));
+	strscpy_pad(m->u.user.name, name, sizeof(m->u.user.name));
 
 	*size += off;
 	*dstptr += msize;
@@ -1148,7 +1148,7 @@ void xt_compat_target_from_user(struct xt_entry_target *t, void **dstptr,
 	t->u.user.target_size = tsize;
 	strscpy(name, target->name, sizeof(name));
 	module_put(target->me);
-	strncpy(t->u.user.name, name, sizeof(t->u.user.name));
+	strscpy_pad(t->u.user.name, name, sizeof(t->u.user.name));
 
 	*size += off;
 	*dstptr += tsize;
@@ -2014,4 +2014,3 @@ static void __exit xt_fini(void)
 
 module_init(xt_init);
 module_exit(xt_fini);
-

-- 
2.41.0.640.ga95def55d0-goog

Re: [PATCH v2 6/7] netfilter: x_tables: refactor deprecated strncpy

[Florian Westphal]

Justin Stitt <justinstitt@google.com> wrote:
> Prefer `strscpy_pad` to `strncpy`.

I don't think this instance needs _pad.

[PATCH v2 7/7] netfilter: xtables: refactor deprecated strncpy

[Justin Stitt]

Prefer `strscpy_pad` as it's a more robust interface whilst maintaing
zero-padding behavior.

There may have existed a bug here due to both `tbl->repl.name` and
`info->name` having a size of 32 as defined below:
|  #define XT_TABLE_MAXNAMELEN 32

This may lead to buffer overreads in some situations -- `strscpy` solves
this by guaranteeing NUL-termination of the dest buffer.

Signed-off-by: Justin Stitt <justinstitt@google.com>

---
Note: build tested only
---
 net/netfilter/xt_repldata.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/xt_repldata.h b/net/netfilter/xt_repldata.h
index 68ccbe50bb1e..5d1fb7018dba 100644
--- a/net/netfilter/xt_repldata.h
+++ b/net/netfilter/xt_repldata.h
@@ -29,7 +29,7 @@
 	if (tbl == NULL) \
 		return NULL; \
 	term = (struct type##_error *)&(((char *)tbl)[term_offset]); \
-	strncpy(tbl->repl.name, info->name, sizeof(tbl->repl.name)); \
+	strscpy_pad(tbl->repl.name, info->name, sizeof(tbl->repl.name)); \
 	*term = (struct type##_error)typ2##_ERROR_INIT;  \
 	tbl->repl.valid_hooks = hook_mask; \
 	tbl->repl.num_entries = nhooks + 1; \

-- 
2.41.0.640.ga95def55d0-goog

Re: [PATCH v2 7/7] netfilter: xtables: refactor deprecated strncpy

[Florian Westphal]

Justin Stitt <justinstitt@google.com> wrote:
> Prefer `strscpy_pad` as it's a more robust interface whilst maintaing
> zero-padding behavior.
> 
> There may have existed a bug here due to both `tbl->repl.name` and
> `info->name` having a size of 32 as defined below:
> |  #define XT_TABLE_MAXNAMELEN 32
> 
> This may lead to buffer overreads in some situations -- `strscpy` solves
> this by guaranteeing NUL-termination of the dest buffer.

I don't think we need to use _pad here.