[PATCH v2] dhcp: Remove option 255 length byte

[PATCH v2] dhcp: Remove option 255 length byte

[Enrique Llorente]

The option 255 (end of options) do not need the length byte, this change
remove that allowing to have one extra byte at other dynamic options.

Signed-off-by: Enrique Llorente <ellorent@redhat.com>
---
 dhcp.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/dhcp.c b/dhcp.c
index 401cb5b..4a209f1 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -64,9 +64,9 @@ static struct opt opts[255];
 #define OPT_MIN		60 /* RFC 951 */
 
 /* Total option size (excluding end option) is 576 (RFC 2131), minus
- * offset of options (268), minus end option and its length (2).
+ * offset of options (268), minus end option (1).
  */
-#define OPT_MAX		306
+#define OPT_MAX		307
 
 /**
  * dhcp_init() - Initialise DHCP options
@@ -127,7 +127,7 @@ struct msg {
 	uint8_t sname[64];
 	uint8_t file[128];
 	uint32_t magic;
-	uint8_t o[OPT_MAX + 2 /* End option and its length */ ];
+	uint8_t o[OPT_MAX + 1 /* End option */ ];
 } __attribute__((__packed__));
 
 /**
@@ -194,7 +194,6 @@ static int fill(struct msg *m)
 	}
 
 	m->o[offset++] = 255;
-	m->o[offset++] = 0;
 
 	if (offset < OPT_MIN) {
 		memset(&m->o[offset], 0, OPT_MIN - offset);
-- 
@@ -64,9 +64,9 @@ static struct opt opts[255];
 #define OPT_MIN		60 /* RFC 951 */
 
 /* Total option size (excluding end option) is 576 (RFC 2131), minus
- * offset of options (268), minus end option and its length (2).
+ * offset of options (268), minus end option (1).
  */
-#define OPT_MAX		306
+#define OPT_MAX		307
 
 /**
  * dhcp_init() - Initialise DHCP options
@@ -127,7 +127,7 @@ struct msg {
 	uint8_t sname[64];
 	uint8_t file[128];
 	uint32_t magic;
-	uint8_t o[OPT_MAX + 2 /* End option and its length */ ];
+	uint8_t o[OPT_MAX + 1 /* End option */ ];
 } __attribute__((__packed__));
 
 /**
@@ -194,7 +194,6 @@ static int fill(struct msg *m)
 	}
 
 	m->o[offset++] = 255;
-	m->o[offset++] = 0;
 
 	if (offset < OPT_MIN) {
 		memset(&m->o[offset], 0, OPT_MIN - offset);
-- 
2.47.0

Re: [PATCH v2] dhcp: Remove option 255 length byte

[David Gibson]

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On Mon, Feb 17, 2025 at 10:28:14AM +0100, Enrique Llorente wrote:
> The option 255 (end of options) do not need the length byte, this change
> remove that allowing to have one extra byte at other dynamic options.
> 
> Signed-off-by: Enrique Llorente <ellorent@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
>  dhcp.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/dhcp.c b/dhcp.c
> index 401cb5b..4a209f1 100644
> --- a/dhcp.c
> +++ b/dhcp.c
> @@ -64,9 +64,9 @@ static struct opt opts[255];
>  #define OPT_MIN		60 /* RFC 951 */
>  
>  /* Total option size (excluding end option) is 576 (RFC 2131), minus
> - * offset of options (268), minus end option and its length (2).
> + * offset of options (268), minus end option (1).
>   */
> -#define OPT_MAX		306
> +#define OPT_MAX		307
>  
>  /**
>   * dhcp_init() - Initialise DHCP options
> @@ -127,7 +127,7 @@ struct msg {
>  	uint8_t sname[64];
>  	uint8_t file[128];
>  	uint32_t magic;
> -	uint8_t o[OPT_MAX + 2 /* End option and its length */ ];
> +	uint8_t o[OPT_MAX + 1 /* End option */ ];
>  } __attribute__((__packed__));
>  
>  /**
> @@ -194,7 +194,6 @@ static int fill(struct msg *m)
>  	}
>  
>  	m->o[offset++] = 255;
> -	m->o[offset++] = 0;
>  
>  	if (offset < OPT_MIN) {
>  		memset(&m->o[offset], 0, OPT_MIN - offset);

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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Re: [PATCH v2] dhcp: Remove option 255 length byte

[Stefano Brivio]

On Mon, 17 Feb 2025 10:28:14 +0100
Enrique Llorente <ellorent@redhat.com> wrote:

> The option 255 (end of options) do not need the length byte, this change
> remove that allowing to have one extra byte at other dynamic options.
> 
> Signed-off-by: Enrique Llorente <ellorent@redhat.com>

Applied.

-- 
Stefano