[PATCH] dhcp: Remove option 255 length byte

[PATCH] 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 | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/dhcp.c b/dhcp.c
index 401cb5b..3aef13f 100644
--- a/dhcp.c
+++ b/dhcp.c
@@ -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);
-- 
@@ -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] dhcp: Remove option 255 length byte

[David Gibson]

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On Tue, Feb 11, 2025 at 12:14:34PM +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>

Thanks, change is good.  However, could you also update the comment on
OPT_MAX's definition that appears to have the same error in it.

> ---
>  dhcp.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/dhcp.c b/dhcp.c
> index 401cb5b..3aef13f 100644
> --- a/dhcp.c
> +++ b/dhcp.c
> @@ -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] dhcp: Remove option 255 length byte

[Stefano Brivio]

On Wed, 12 Feb 2025 12:14:32 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> On Tue, Feb 11, 2025 at 12:14:34PM +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>  
> 
> Thanks, change is good.  However, could you also update the comment on
> OPT_MAX's definition that appears to have the same error in it.

I was about to apply this by amending the comment, but... it's not just
the comment (hence it needs to be re-tested a bit): OPT_MAX should be
307 now, otherwise you don't actually use the extra byte.

-- 
Stefano

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

[Enrique Llorente Pastora]

On Wed, Feb 12, 2025 at 2:38 AM Stefano Brivio <sbrivio@redhat.com> wrote:
>
> On Wed, 12 Feb 2025 12:14:32 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
>
> > On Tue, Feb 11, 2025 at 12:14:34PM +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>
> >
> > Thanks, change is good.  However, could you also update the comment on
> > OPT_MAX's definition that appears to have the same error in it.
>
> I was about to apply this by amending the comment, but... it's not just
> the comment (hence it needs to be re-tested a bit): OPT_MAX should be
> 307 now, otherwise you don't actually use the extra byte.
>

Good catch, changing.

> --
> Stefano
>


-- 
Quique Llorente

CNV networking Senior Software Engineer

Red Hat EMEA

ellorent@redhat.com

@RedHat   Red Hat  Red Hat