On Mon, Jun 01, 2026 at 01:07:55PM +0530, Anshu Kumari wrote: > A user can enter lots of options in command-line which may not fit in > existing buffer, So when the options field is full, overflow remaining > DHCP options into the file and sname fields per RFC 2132 option 52. > > Also, when the file field is not used for overload, copy the boot > file URL there directly for legacy PXE clients. > > Link: https://bugs.passt.top/show_bug.cgi?id=192 > Signed-off-by: Anshu Kumari Reviewed-by: David Gibson For the code proper. The commit message is perhaps buries the lede in that in that this is also the patch that actually starts putting the custom_opts into DHCP replies. Mind you, that would change if we parsed directly into opts[], which might be nicer anyway. > --- > v3: > - Added RFC 2132 Section 9.3 reference comment on overload > constants. > - Use ARRAY_SIZE(opts) instead of raw 255 in fill_overflow(). > - Swapped overflow order: try sname (64 bytes) first, then file > (128 bytes) — better packing and keeps file field available for > boot file name. > - Removed '&' from &reply.file. > - Removed '+1' from memcpy — reply.file already zeroed. > - opt_set_dns_search() max_len: OPT_MAX - 3 instead of > sizeof(m->o). > > v2: > - Added #define DHCP_OVERLOAD_FILE and #define DHCP_OVERLOAD_SNAME constants > - Added comment documenting space reservation: /* Reserve 3 bytes for option 52 */ > - Fixed DNS search length: sizeof(m->o) only, not combined with file+sname > - Removed dhcp_boot references — reply.file copy now reads from opts[67] > - Used DHCP_OVERLOAD_FILE constant in reply.file guard > --- > dhcp.c | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 81 insertions(+), 10 deletions(-) > > diff --git a/dhcp.c b/dhcp.c > index 5c6a492..a9d56fd 100644 > --- a/dhcp.c > +++ b/dhcp.c > @@ -372,14 +372,64 @@ static bool fill_one(uint8_t *buf, size_t size, int o, int *offset) > return false; > } > > +/* RFC 2132, Section 9.3 - Option Overload*/ > +#define DHCP_OVERLOAD_FILE 1 > +#define DHCP_OVERLOAD_SNAME 2 > + > /** > - * fill() - Fill options in message > + * fill_overflow() - Fill remaining options into sname and file fields > + * @m: Message whose sname/file fields may be used for overflow > + * > + * Try the smaller sname field first: small options go there, leaving > + * the larger file field available for big options and for the boot > + * file name (option 67) if set. > + * > + * Return: option 52 overload value: 0 if no overflow, > + * DHCP_OVERLOAD_FILE for file, DHCP_OVERLOAD_SNAME for sname, > + * or both OR'd together > + */ > +static int fill_overflow(struct msg *m) > +{ > + int sname_off = 0, file_off = 0, overload = 0; > + int o; > + > + for (o = 0; (size_t)o < ARRAY_SIZE(opts); o++) { > + if (opts[o].slen == -1 || opts[o].sent) > + continue; > + fill_one(m->sname, sizeof(m->sname) - 1, o, &sname_off); > + } > + > + for (o = 0; (size_t)o < ARRAY_SIZE(opts); o++) { > + if (opts[o].slen == -1 || opts[o].sent) > + continue; > + if (fill_one(m->file, sizeof(m->file) - 1, o, &file_off)) > + debug("DHCP: skipping option %i (overload full)", o); > + } > + > + if (sname_off) { > + m->sname[sname_off] = 255; > + overload |= DHCP_OVERLOAD_SNAME; > + } > + > + if (file_off) { > + m->file[file_off] = 255; > + overload |= DHCP_OVERLOAD_FILE; > + } > + > + return overload; > +} > + > +/** > + * fill() - Fill options in message, with overload into file/sname if needed > * @m: Message to fill > + * @overload: Set to option 52 value (0 if none, 1/2/3 per RFC 2132) > * > * Return: current size of options field > */ > -static int fill(struct msg *m) > +static int fill(struct msg *m, int *overload) > { > + /* Reserve 3 bytes for option 52 (overload) if needed */ > + size_t size = OPT_MAX - 3; > int i, o, offset = 0; > > for (o = 0; o < 255; o++) > @@ -390,20 +440,25 @@ static int fill(struct msg *m) > * Put it there explicitly, unless requested via option 55. > */ > if (opts[55].clen > 0 && !memchr(opts[55].c, 53, opts[55].clen)) > - if (fill_one(m->o, OPT_MAX, 53, &offset)) > - debug("DHCP: skipping option 53"); > + fill_one(m->o, size, 53, &offset); > > for (i = 0; i < opts[55].clen; i++) { > o = opts[55].c[i]; > if (opts[o].slen != -1) > - if (fill_one(m->o, OPT_MAX, o, &offset)) > - debug("DHCP: skipping option %i", o); > + fill_one(m->o, size, o, &offset); > } > > for (o = 0; o < 255; o++) { > if (opts[o].slen != -1 && !opts[o].sent) > - if (fill_one(m->o, OPT_MAX, o, &offset)) > - debug("DHCP: skipping option %i", o); > + fill_one(m->o, size, o, &offset); > + } > + > + *overload = fill_overflow(m); > + > + if (*overload) { > + m->o[offset++] = 52; > + m->o[offset++] = 1; > + m->o[offset++] = *overload; > } > > m->o[offset++] = 255; > @@ -528,6 +583,7 @@ int dhcp(const struct ctx *c, struct iov_tail *data) > struct msg const *m; > struct msg reply; > unsigned int i; > + int overload; > > eh = IOV_REMOVE_HEADER(data, eh_storage); > iph = IOV_PEEK_HEADER(data, iph_storage); > @@ -677,9 +733,24 @@ int dhcp(const struct ctx *c, struct iov_tail *data) > } > > if (!c->no_dhcp_dns_search) > - opt_set_dns_search(c, sizeof(m->o)); > + opt_set_dns_search(c, OPT_MAX - 3); > + > + for (i = 0; i < (unsigned int)c->custom_opts_count; i++) { > + uint8_t code = c->custom_opts[i].code; > + > + opts[code].slen = c->custom_opts[i].len; > + memcpy(opts[code].s, c->custom_opts[i].val, > + c->custom_opts[i].len); > + } > + > + dlen = offsetof(struct msg, o) + fill(&reply, &overload); > > - dlen = offsetof(struct msg, o) + fill(&reply); > + /* Copy boot file name into the file field for legacy PXE clients, > + * unless the file field is already used for option overload. > + */ > + if (!(overload & DHCP_OVERLOAD_FILE) && > + opts[67].slen > 0 && (size_t)opts[67].slen < sizeof(reply.file)) > + memcpy(reply.file, opts[67].s, opts[67].slen); > > if (m->flags & FLAG_BROADCAST) > dst = in4addr_broadcast; > -- > 2.54.0 > -- 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