[PATCH net-next 1/2] keys, dns: drop unused upayload->data NUL terminator

[PATCH net-next 1/2] keys, dns: drop unused upayload->data NUL terminator

[Thorsten Blum]

In dns_resolver_preparse(), do not NUL-terminate ->data and allocate one
byte less. The NUL terminator is never used and only ->datalen bytes are
accessed.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 net/dns_resolver/dns_key.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
index c3c8c3240ef9..451247864a63 100644
--- a/net/dns_resolver/dns_key.c
+++ b/net/dns_resolver/dns_key.c
@@ -203,7 +203,7 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
 	kdebug("store result");
 	prep->quotalen = result_len;
 
-	upayload = kmalloc_flex(*upayload, data, result_len + 1);
+	upayload = kmalloc_flex(*upayload, data, result_len);
 	if (!upayload) {
 		kleave(" = -ENOMEM");
 		return -ENOMEM;
@@ -211,7 +211,6 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
 
 	upayload->datalen = result_len;
 	memcpy(upayload->data, data, result_len);
-	upayload->data[result_len] = '\0';
 
 	prep->payload.data[dns_key_data] = upayload;
 	kleave(" = 0");

[PATCH net-next 2/2] KEYS: annotate struct user_key_payload with __counted_by

[Thorsten Blum]

Add the __counted_by() compiler attribute to the flexible array member
'data' to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 include/keys/user-type.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/keys/user-type.h b/include/keys/user-type.h
index 386c31432789..2305991f4fcd 100644
--- a/include/keys/user-type.h
+++ b/include/keys/user-type.h
@@ -27,7 +27,8 @@
 struct user_key_payload {
 	struct rcu_head	rcu;		/* RCU destructor */
 	unsigned short	datalen;	/* length of this data */
-	char		data[] __aligned(__alignof__(u64)); /* actual data */
+	char		data[]		/* actual data */
+			__aligned(__alignof__(u64)) __counted_by(datalen);
 };
 
 extern struct key_type key_type_user;

Re: [PATCH net-next 2/2] KEYS: annotate struct user_key_payload with __counted_by

[Jarkko Sakkinen]

On Mon, Apr 06, 2026 at 07:58:10PM +0200, Thorsten Blum wrote:
> Add the __counted_by() compiler attribute to the flexible array member
> 'data' to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> CONFIG_FORTIFY_SOURCE.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
>  include/keys/user-type.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/keys/user-type.h b/include/keys/user-type.h
> index 386c31432789..2305991f4fcd 100644
> --- a/include/keys/user-type.h
> +++ b/include/keys/user-type.h
> @@ -27,7 +27,8 @@
>  struct user_key_payload {
>  	struct rcu_head	rcu;		/* RCU destructor */
>  	unsigned short	datalen;	/* length of this data */
> -	char		data[] __aligned(__alignof__(u64)); /* actual data */
> +	char		data[]		/* actual data */
> +			__aligned(__alignof__(u64)) __counted_by(datalen);
>  };
>  
>  extern struct key_type key_type_user;

You don't provide any evidence of any improvement.

BR, Jarkko

Re: [PATCH net-next 2/2] KEYS: annotate struct user_key_payload with __counted_by

[Thorsten Blum]

On Wed, Apr 08, 2026 at 12:02:25PM +0300, Jarkko Sakkinen wrote:
> On Mon, Apr 06, 2026 at 07:58:10PM +0200, Thorsten Blum wrote:
> > Add the __counted_by() compiler attribute to the flexible array member
> > 'data' to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
> > CONFIG_FORTIFY_SOURCE.
> > 
> > Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> > ---
> >  include/keys/user-type.h | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/keys/user-type.h b/include/keys/user-type.h
> > index 386c31432789..2305991f4fcd 100644
> > --- a/include/keys/user-type.h
> > +++ b/include/keys/user-type.h
> > @@ -27,7 +27,8 @@
> >  struct user_key_payload {
> >  	struct rcu_head	rcu;		/* RCU destructor */
> >  	unsigned short	datalen;	/* length of this data */
> > -	char		data[] __aligned(__alignof__(u64)); /* actual data */
> > +	char		data[]		/* actual data */
> > +			__aligned(__alignof__(u64)) __counted_by(datalen);
> >  };
> >  
> >  extern struct key_type key_type_user;
> 
> You don't provide any evidence of any improvement.

It's a proactive hardening change to help avoid future mistakes.

The __counted_by() annotation makes the bounds visible to the compiler
and at runtime so that future ->data accesses can be checked against
->datalen.

The current code is correct regarding ->data accesses and doesn't
require any changes.