* [PATCH] netfilter: x_tables: replace strlcat() with snprintf()
@ 2026-06-26 22:25 Ian Bridges
2026-06-27 21:16 ` David Laight
0 siblings, 1 reply; 4+ messages in thread
From: Ian Bridges @ 2026-06-26 22:25 UTC (permalink / raw)
To: Pablo Neira Ayuso, Florian Westphal, Phil Sutter, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, Simon Horman,
netfilter-devel, coreteam, netdev, linux-kernel
Cc: linux-hardening
In preparation for removing the deprecated strlcat() API[1], replace the
strscpy()/strlcat() pairs in xt_proto_init() and xt_proto_fini() with
snprintf(), which builds each /proc file name in a single call.
Each name is "<prefix><suffix>", where <prefix> is the address-family
string xt_prefix[af] and <suffix> is one of the FORMAT_TABLES,
FORMAT_MATCHES or FORMAT_TARGETS literals. snprintf() with a "%s%s"
format produces the same NUL-terminated, length-bounded string as the
strscpy()/strlcat() chain it replaces, so the proc entry names are
unchanged.
Link: https://github.com/KSPP/linux/issues/370 [1]
Signed-off-by: Ian Bridges <icb@fastmail.org>
---
net/netfilter/x_tables.c | 24 ++++++++----------------
1 file changed, 8 insertions(+), 16 deletions(-)
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 4e6708c23922..56f4546be336 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -2033,8 +2033,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
root_uid = make_kuid(net->user_ns, 0);
root_gid = make_kgid(net->user_ns, 0);
- strscpy(buf, xt_prefix[af], sizeof(buf));
- strlcat(buf, FORMAT_TABLES, sizeof(buf));
+ snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
proc = proc_create_net_data(buf, 0440, net->proc_net, &xt_table_seq_ops,
sizeof(struct seq_net_private),
(void *)(unsigned long)af);
@@ -2043,8 +2042,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
if (uid_valid(root_uid) && gid_valid(root_gid))
proc_set_user(proc, root_uid, root_gid);
- strscpy(buf, xt_prefix[af], sizeof(buf));
- strlcat(buf, FORMAT_MATCHES, sizeof(buf));
+ snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
proc = proc_create_seq_private(buf, 0440, net->proc_net,
&xt_match_seq_ops, sizeof(struct nf_mttg_trav),
(void *)(unsigned long)af);
@@ -2053,8 +2051,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
if (uid_valid(root_uid) && gid_valid(root_gid))
proc_set_user(proc, root_uid, root_gid);
- strscpy(buf, xt_prefix[af], sizeof(buf));
- strlcat(buf, FORMAT_TARGETS, sizeof(buf));
+ snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TARGETS);
proc = proc_create_seq_private(buf, 0440, net->proc_net,
&xt_target_seq_ops, sizeof(struct nf_mttg_trav),
(void *)(unsigned long)af);
@@ -2068,13 +2065,11 @@ int xt_proto_init(struct net *net, u_int8_t af)
#ifdef CONFIG_PROC_FS
out_remove_matches:
- strscpy(buf, xt_prefix[af], sizeof(buf));
- strlcat(buf, FORMAT_MATCHES, sizeof(buf));
+ snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
remove_proc_entry(buf, net->proc_net);
out_remove_tables:
- strscpy(buf, xt_prefix[af], sizeof(buf));
- strlcat(buf, FORMAT_TABLES, sizeof(buf));
+ snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
remove_proc_entry(buf, net->proc_net);
out:
return -1;
@@ -2087,16 +2082,13 @@ void xt_proto_fini(struct net *net, u_int8_t af)
#ifdef CONFIG_PROC_FS
char buf[XT_FUNCTION_MAXNAMELEN];
- strscpy(buf, xt_prefix[af], sizeof(buf));
- strlcat(buf, FORMAT_TABLES, sizeof(buf));
+ snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
remove_proc_entry(buf, net->proc_net);
- strscpy(buf, xt_prefix[af], sizeof(buf));
- strlcat(buf, FORMAT_TARGETS, sizeof(buf));
+ snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TARGETS);
remove_proc_entry(buf, net->proc_net);
- strscpy(buf, xt_prefix[af], sizeof(buf));
- strlcat(buf, FORMAT_MATCHES, sizeof(buf));
+ snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
remove_proc_entry(buf, net->proc_net);
#endif /*CONFIG_PROC_FS*/
}
--
2.47.3
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] netfilter: x_tables: replace strlcat() with snprintf()
2026-06-26 22:25 [PATCH] netfilter: x_tables: replace strlcat() with snprintf() Ian Bridges
@ 2026-06-27 21:16 ` David Laight
2026-07-01 6:25 ` Ian Bridges
0 siblings, 1 reply; 4+ messages in thread
From: David Laight @ 2026-06-27 21:16 UTC (permalink / raw)
To: Ian Bridges
Cc: Pablo Neira Ayuso, Florian Westphal, Phil Sutter, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, Simon Horman,
netfilter-devel, coreteam, netdev, linux-kernel, linux-hardening
On Fri, 26 Jun 2026 17:25:35 -0500
Ian Bridges <icb@fastmail.org> wrote:
> In preparation for removing the deprecated strlcat() API[1], replace the
> strscpy()/strlcat() pairs in xt_proto_init() and xt_proto_fini() with
> snprintf(), which builds each /proc file name in a single call.
>
> Each name is "<prefix><suffix>", where <prefix> is the address-family
> string xt_prefix[af] and <suffix> is one of the FORMAT_TABLES,
> FORMAT_MATCHES or FORMAT_TARGETS literals. snprintf() with a "%s%s"
> format produces the same NUL-terminated, length-bounded string as the
> strscpy()/strlcat() chain it replaces, so the proc entry names are
> unchanged.
>
> Link: https://github.com/KSPP/linux/issues/370 [1]
> Signed-off-by: Ian Bridges <icb@fastmail.org>
> ---
> net/netfilter/x_tables.c | 24 ++++++++----------------
> 1 file changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index 4e6708c23922..56f4546be336 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -2033,8 +2033,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
> root_uid = make_kuid(net->user_ns, 0);
> root_gid = make_kgid(net->user_ns, 0);
>
> - strscpy(buf, xt_prefix[af], sizeof(buf));
> - strlcat(buf, FORMAT_TABLES, sizeof(buf));
> + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
If you are going to use snprintf either paste the strings together:
snprintf(buf, sizeof(buf), "%s" FORMAT_TABLES, xt_prefix[af]);
or prepend the "%s" onto the #define of FORMAT_TABLES itself:
snprintf(buf, sizeof(buf), FORMAT_TABLES, xt_prefix[af]);
FORMAT_TABLES should also be FORMAT_NAMES.
-- David
> proc = proc_create_net_data(buf, 0440, net->proc_net, &xt_table_seq_ops,
> sizeof(struct seq_net_private),
> (void *)(unsigned long)af);
> @@ -2043,8 +2042,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
> if (uid_valid(root_uid) && gid_valid(root_gid))
> proc_set_user(proc, root_uid, root_gid);
>
> - strscpy(buf, xt_prefix[af], sizeof(buf));
> - strlcat(buf, FORMAT_MATCHES, sizeof(buf));
> + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
> proc = proc_create_seq_private(buf, 0440, net->proc_net,
> &xt_match_seq_ops, sizeof(struct nf_mttg_trav),
> (void *)(unsigned long)af);
> @@ -2053,8 +2051,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
> if (uid_valid(root_uid) && gid_valid(root_gid))
> proc_set_user(proc, root_uid, root_gid);
>
> - strscpy(buf, xt_prefix[af], sizeof(buf));
> - strlcat(buf, FORMAT_TARGETS, sizeof(buf));
> + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TARGETS);
> proc = proc_create_seq_private(buf, 0440, net->proc_net,
> &xt_target_seq_ops, sizeof(struct nf_mttg_trav),
> (void *)(unsigned long)af);
> @@ -2068,13 +2065,11 @@ int xt_proto_init(struct net *net, u_int8_t af)
>
> #ifdef CONFIG_PROC_FS
> out_remove_matches:
> - strscpy(buf, xt_prefix[af], sizeof(buf));
> - strlcat(buf, FORMAT_MATCHES, sizeof(buf));
> + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
> remove_proc_entry(buf, net->proc_net);
>
> out_remove_tables:
> - strscpy(buf, xt_prefix[af], sizeof(buf));
> - strlcat(buf, FORMAT_TABLES, sizeof(buf));
> + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
> remove_proc_entry(buf, net->proc_net);
> out:
> return -1;
> @@ -2087,16 +2082,13 @@ void xt_proto_fini(struct net *net, u_int8_t af)
> #ifdef CONFIG_PROC_FS
> char buf[XT_FUNCTION_MAXNAMELEN];
>
> - strscpy(buf, xt_prefix[af], sizeof(buf));
> - strlcat(buf, FORMAT_TABLES, sizeof(buf));
> + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
> remove_proc_entry(buf, net->proc_net);
>
> - strscpy(buf, xt_prefix[af], sizeof(buf));
> - strlcat(buf, FORMAT_TARGETS, sizeof(buf));
> + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TARGETS);
> remove_proc_entry(buf, net->proc_net);
>
> - strscpy(buf, xt_prefix[af], sizeof(buf));
> - strlcat(buf, FORMAT_MATCHES, sizeof(buf));
> + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
> remove_proc_entry(buf, net->proc_net);
> #endif /*CONFIG_PROC_FS*/
> }
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] netfilter: x_tables: replace strlcat() with snprintf()
2026-06-27 21:16 ` David Laight
@ 2026-07-01 6:25 ` Ian Bridges
2026-07-01 6:31 ` Florian Westphal
0 siblings, 1 reply; 4+ messages in thread
From: Ian Bridges @ 2026-07-01 6:25 UTC (permalink / raw)
To: David Laight
Cc: Pablo Neira Ayuso, Florian Westphal, Phil Sutter, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, Simon Horman,
netfilter-devel, coreteam, netdev, linux-kernel, linux-hardening
On Sat, Jun 27, 2026 at 10:16:43PM +0100, David Laight wrote:
> On Fri, 26 Jun 2026 17:25:35 -0500
> Ian Bridges <icb@fastmail.org> wrote:
>
> > In preparation for removing the deprecated strlcat() API[1], replace the
> > strscpy()/strlcat() pairs in xt_proto_init() and xt_proto_fini() with
> > snprintf(), which builds each /proc file name in a single call.
> >
> > Each name is "<prefix><suffix>", where <prefix> is the address-family
> > string xt_prefix[af] and <suffix> is one of the FORMAT_TABLES,
> > FORMAT_MATCHES or FORMAT_TARGETS literals. snprintf() with a "%s%s"
> > format produces the same NUL-terminated, length-bounded string as the
> > strscpy()/strlcat() chain it replaces, so the proc entry names are
> > unchanged.
> >
> > Link: https://github.com/KSPP/linux/issues/370 [1]
> > Signed-off-by: Ian Bridges <icb@fastmail.org>
> > ---
> > net/netfilter/x_tables.c | 24 ++++++++----------------
> > 1 file changed, 8 insertions(+), 16 deletions(-)
> >
> > diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> > index 4e6708c23922..56f4546be336 100644
> > --- a/net/netfilter/x_tables.c
> > +++ b/net/netfilter/x_tables.c
> > @@ -2033,8 +2033,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
> > root_uid = make_kuid(net->user_ns, 0);
> > root_gid = make_kgid(net->user_ns, 0);
> >
> > - strscpy(buf, xt_prefix[af], sizeof(buf));
> > - strlcat(buf, FORMAT_TABLES, sizeof(buf));
> > + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
>
> If you are going to use snprintf either paste the strings together:
> snprintf(buf, sizeof(buf), "%s" FORMAT_TABLES, xt_prefix[af]);
> or prepend the "%s" onto the #define of FORMAT_TABLES itself:
> snprintf(buf, sizeof(buf), FORMAT_TABLES, xt_prefix[af]);
>
I learned something new today, thanks. I'll use the first form in v2.
> FORMAT_TABLES should also be FORMAT_NAMES.
The macro is already named FORMAT_TABLES today, so that rename would
be a cleanup of pre-existing code rather than part of the strlcat
conversion. I'm happy to fold it into v2 if a maintainer is fine
including the tidy-up in this patch.
Thanks for the review,
Ian
>
> -- David
>
> > proc = proc_create_net_data(buf, 0440, net->proc_net, &xt_table_seq_ops,
> > sizeof(struct seq_net_private),
> > (void *)(unsigned long)af);
> > @@ -2043,8 +2042,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
> > if (uid_valid(root_uid) && gid_valid(root_gid))
> > proc_set_user(proc, root_uid, root_gid);
> >
> > - strscpy(buf, xt_prefix[af], sizeof(buf));
> > - strlcat(buf, FORMAT_MATCHES, sizeof(buf));
> > + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
> > proc = proc_create_seq_private(buf, 0440, net->proc_net,
> > &xt_match_seq_ops, sizeof(struct nf_mttg_trav),
> > (void *)(unsigned long)af);
> > @@ -2053,8 +2051,7 @@ int xt_proto_init(struct net *net, u_int8_t af)
> > if (uid_valid(root_uid) && gid_valid(root_gid))
> > proc_set_user(proc, root_uid, root_gid);
> >
> > - strscpy(buf, xt_prefix[af], sizeof(buf));
> > - strlcat(buf, FORMAT_TARGETS, sizeof(buf));
> > + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TARGETS);
> > proc = proc_create_seq_private(buf, 0440, net->proc_net,
> > &xt_target_seq_ops, sizeof(struct nf_mttg_trav),
> > (void *)(unsigned long)af);
> > @@ -2068,13 +2065,11 @@ int xt_proto_init(struct net *net, u_int8_t af)
> >
> > #ifdef CONFIG_PROC_FS
> > out_remove_matches:
> > - strscpy(buf, xt_prefix[af], sizeof(buf));
> > - strlcat(buf, FORMAT_MATCHES, sizeof(buf));
> > + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
> > remove_proc_entry(buf, net->proc_net);
> >
> > out_remove_tables:
> > - strscpy(buf, xt_prefix[af], sizeof(buf));
> > - strlcat(buf, FORMAT_TABLES, sizeof(buf));
> > + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
> > remove_proc_entry(buf, net->proc_net);
> > out:
> > return -1;
> > @@ -2087,16 +2082,13 @@ void xt_proto_fini(struct net *net, u_int8_t af)
> > #ifdef CONFIG_PROC_FS
> > char buf[XT_FUNCTION_MAXNAMELEN];
> >
> > - strscpy(buf, xt_prefix[af], sizeof(buf));
> > - strlcat(buf, FORMAT_TABLES, sizeof(buf));
> > + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TABLES);
> > remove_proc_entry(buf, net->proc_net);
> >
> > - strscpy(buf, xt_prefix[af], sizeof(buf));
> > - strlcat(buf, FORMAT_TARGETS, sizeof(buf));
> > + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_TARGETS);
> > remove_proc_entry(buf, net->proc_net);
> >
> > - strscpy(buf, xt_prefix[af], sizeof(buf));
> > - strlcat(buf, FORMAT_MATCHES, sizeof(buf));
> > + snprintf(buf, sizeof(buf), "%s%s", xt_prefix[af], FORMAT_MATCHES);
> > remove_proc_entry(buf, net->proc_net);
> > #endif /*CONFIG_PROC_FS*/
> > }
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] netfilter: x_tables: replace strlcat() with snprintf()
2026-07-01 6:25 ` Ian Bridges
@ 2026-07-01 6:31 ` Florian Westphal
0 siblings, 0 replies; 4+ messages in thread
From: Florian Westphal @ 2026-07-01 6:31 UTC (permalink / raw)
To: Ian Bridges
Cc: David Laight, Pablo Neira Ayuso, Phil Sutter, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, Simon Horman,
netfilter-devel, coreteam, netdev, linux-kernel, linux-hardening
Ian Bridges <icb@fastmail.org> wrote:
> I learned something new today, thanks. I'll use the first form in v2.
>
> > FORMAT_TABLES should also be FORMAT_NAMES.
No. The name is fine.
> The macro is already named FORMAT_TABLES today, so that rename would
> be a cleanup of pre-existing code rather than part of the strlcat
> conversion. I'm happy to fold it into v2 if a maintainer is fine
> including the tidy-up in this patch.
No need for a v2, I mangled this patch locally already to use
"%s_FOO" in FORMAT_FOO.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2026-06-26 22:25 [PATCH] netfilter: x_tables: replace strlcat() with snprintf() Ian Bridges
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2026-07-01 6:25 ` Ian Bridges
2026-07-01 6:31 ` Florian Westphal
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