On Thu, Feb 05, 2026 at 05:03:09PM -0500, Jon Maloy wrote: > Extend the -a/--address option to accept addresses in CIDR notation > (e.g., 192.168.1.1/24 or 2001:db8::1/64) as an alternative to using > separate -a and -n options. > > We add a new inany_prefix_pton() helper function that: > - Parses address strings with a compulsory /prefix_len suffix > - Validates prefix length based on address family (0-32 for IPv4, > 0-128 for IPv6), including handling of IPv4-to-IPv6 mapping case. > > For IPv4, the prefix length is stored in ip4.prefix_len when provided. > Mixing -n and CIDR notation results in an error to catch likely user > mistakes. > > Also fix a bug in conf_ip4_prefix() that was incorrectly using the > global 'optarg' instead of its 'arg' parameter. > > Signed-off-by: Jon Maloy > > --- > v3: Fixes after feedback from Laurent, David and Stefano > Notably, updated man page for the -a option > > v4: Fixes based on feedback from David G: > - Handling prefix length adjustment when IPv4-to-IPv6 mapping > - Removed redundant !IN6_IS_ADDR_V4MAPPED(&addr.a6) test > - Simplified tests of acceptable address types > - Merged documentation and code commits > - Some documentation text clarifications > > v5: - Moved address/prefix parsing into a refactored > inany_prefix_pton() function. > - inany_prefix_pton() now only caluclates IPv6 style > prefix lengths > - Stricter distinction between error causes. > - Some refactoring of the 'case a:' branch in conf() > - Some small fixes in passt.1 > > v6: - Refactored inany_prefix_pton() and conf()::'case -a' > code after input from David Gibson. > --- > conf.c | 56 +++++++++++++++++++++++++++++++++----------------------- > inany.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > inany.h | 14 ++++++++++++++ > ip.c | 21 +++++++++++++++++++++ > ip.h | 2 ++ > passt.1 | 17 ++++++++++++----- > 6 files changed, 134 insertions(+), 28 deletions(-) > > diff --git a/conf.c b/conf.c > index 2942c8c..3cf825e 100644 > --- a/conf.c > +++ b/conf.c > @@ -682,7 +682,7 @@ static int conf_ip4_prefix(const char *arg) > return -1; > } else { > errno = 0; > - len = strtoul(optarg, NULL, 0); > + len = strtoul(arg, NULL, 0); > if (len > 32 || errno) > return -1; > } > @@ -896,7 +896,7 @@ static void usage(const char *name, FILE *f, int status) > " a zero value disables assignment\n" > " default: 65520: maximum 802.3 MTU minus 802.3 header\n" > " length, rounded to 32 bits (IPv4 words)\n" > - " -a, --address ADDR Assign IPv4 or IPv6 address ADDR\n" > + " -a, --address ADDR Assign IPv4 or IPv6 address ADDR[/PREFIXLEN]\n" > " can be specified zero to two times (for IPv4 and IPv6)\n" > " default: use addresses from interface with default route\n" > " -n, --netmask MASK Assign IPv4 MASK, dot-decimal or bits\n" > @@ -1498,6 +1498,7 @@ void conf(struct ctx *c, int argc, char **argv) > const char *optstring = "+dqfel:hs:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:"; > const char *logname = (c->mode == MODE_PASTA) ? "pasta" : "passt"; > char userns[PATH_MAX] = { 0 }, netns[PATH_MAX] = { 0 }; > + bool prefix_from_cidr = false, prefix_from_opt = false; > bool copy_addrs_opt = false, copy_routes_opt = false; > enum fwd_ports_mode fwd_default = FWD_NONE; > bool v4_only = false, v6_only = false; > @@ -1808,35 +1809,44 @@ void conf(struct ctx *c, int argc, char **argv) > c->mtu = mtu; > break; > } > - case 'a': > - if (inet_pton(AF_INET6, optarg, &c->ip6.addr) && > - !IN6_IS_ADDR_UNSPECIFIED(&c->ip6.addr) && > - !IN6_IS_ADDR_LOOPBACK(&c->ip6.addr) && > - !IN6_IS_ADDR_V4MAPPED(&c->ip6.addr) && > - !IN6_IS_ADDR_V4COMPAT(&c->ip6.addr) && > - !IN6_IS_ADDR_MULTICAST(&c->ip6.addr)) { > - if (c->mode == MODE_PASTA) > - c->ip6.no_copy_addrs = true; > - break; > - } > - > - if (inet_pton(AF_INET, optarg, &c->ip4.addr) && > - !IN4_IS_ADDR_UNSPECIFIED(&c->ip4.addr) && > - !IN4_IS_ADDR_BROADCAST(&c->ip4.addr) && > - !IN4_IS_ADDR_LOOPBACK(&c->ip4.addr) && > - !IN4_IS_ADDR_MULTICAST(&c->ip4.addr)) { > + case 'a': { > + union inany_addr addr; > + int prefix_len; > + > + if (inany_pton(optarg, &addr)) > + prefix_len = inany_default_prefix_len(&addr); If the command line specified -n before -a, this will clobber the value stored by -n. > + else if (!inany_prefix_pton(optarg, &addr, &prefix_len)) > + die("Invalid address/prefix_len: %s", optarg); > + else if (prefix_from_opt) > + die("Can't mix CIDR with -n"); > + else > + prefix_from_cidr = true; > + > + if (inany_is_unspecified(&addr) || > + inany_is_multicast(&addr) || > + inany_is_loopback(&addr) || > + IN6_IS_ADDR_V4COMPAT(&addr.a6)) > + die("Invalid address: %s", optarg); > + > + if (inany_v4(&addr)) { > + c->ip4.addr = *inany_v4(&addr); > + c->ip4.prefix_len = prefix_len - 96; > if (c->mode == MODE_PASTA) > c->ip4.no_copy_addrs = true; > - break; > + } else { > + c->ip6.addr = addr.a6; > + if (c->mode == MODE_PASTA) > + c->ip6.no_copy_addrs = true; > } > - > - die("Invalid address: %s", optarg); > break; > + } > case 'n': > + if (prefix_from_cidr) > + die("Can't use both -n and CIDR prefix length"); > c->ip4.prefix_len = conf_ip4_prefix(optarg); > if (c->ip4.prefix_len < 0) > die("Invalid netmask: %s", optarg); > - > + prefix_from_opt = true; > break; > case 'M': > parse_mac(c->our_tap_mac, optarg); > diff --git a/inany.c b/inany.c > index 7680439..d9a592a 100644 > --- a/inany.c > +++ b/inany.c > @@ -11,6 +11,7 @@ > #include > #include > #include > +#include > > #include "util.h" > #include "ip.h" > @@ -57,3 +58,54 @@ int inany_pton(const char *src, union inany_addr *dst) > > return 0; > } > + > +/** inany_prefix_pton - Parse an IPv[46] address with prefix length > + * @src: IPv[46] address and prefix length string in CIDR format > + * @dst: output buffer, filled with parsed address > + * @prefix_len: pointer to prefix length > + * > + * Return: on success, 1, if no parseable address or prefix is found, 0 0 on success, -ve error code on error is our usual convention for functions which need to indicate failure. > + */ > +int inany_prefix_pton(char *src, union inany_addr *dst, int *prefix_len) I'd suggest taking prefix_len as a (uint8_t *). That way if you have a data structure which compactly stores a prefix length as a uint8_t, you can parse directly into it without having to copy it via another int. > +{ > + char astr[INANY_ADDRSTRLEN] = {0,}; > + size_t alen = strcspn(src, "/"); > + char pstr[4] = {0,}; > + char *end; > + > + if (alen >= INANY_ADDRSTRLEN) > + return 0; > + > + if (src[alen] != '/') > + return 0; > + > + strncpy(astr, src, alen); > + strncpy(pstr, &src[alen + 1], sizeof(pstr) - 1); No need to copy the prefix length part - you can strtoul() on (src + alen + 1) directly. More importantly, this strncpy() means you'll silently truncate if the string is too long, rather than reporting a parse error. > + > + info("addr %s, prefix %s", astr, pstr); > + > + /* Read prefix length */ > + errno = 0; > + *prefix_len = strtoul(pstr, &end, 10); You want to store this in an unsigned long local and bounds check before storing it to *prefix_len. Otherwise a prefix length of 4294967360 would be silently truncated to 64. > + if (errno || *end) > + return 0; > + > + if (*prefix_len > 128) > + return 0; > + > + /* Read address */ > + if (inet_pton(AF_INET6, astr, dst)) { > + if (!inany_v4(dst)) > + return 1; > + if (*prefix_len < 96) > + return 0; I think interaction of these two conditions is clearer as: if (inany_v4(dst) && prefix_len < 96) return ; > + return 1; > + } else if (inany_pton(astr, dst)) { > + if (*prefix_len > 32) > + return 0; > + *prefix_len += 96; > + return 1; > + } > + > + return 0; > +} > diff --git a/inany.h b/inany.h > index 61b36fb..675e7e7 100644 > --- a/inany.h > +++ b/inany.h > @@ -96,6 +96,19 @@ static inline struct in_addr *inany_v4(const union inany_addr *addr) > return (struct in_addr *)&addr->v4mapped.a4; > } > > +/** inany_default_prefix_len() - Get default prefix length for address > + * @addr: IPv4 or iPv6 address > + * > + * Return: Class-based prefix length for IPv4 (in IPv6 format: 104-128), > + * or 64 for IPv6 > + */ > +static inline int inany_default_prefix_len(const union inany_addr *addr) > +{ > + const struct in_addr *v4 = inany_v4(addr); > + > + return v4 ? ip4_class_prefix_len(v4) : 64; > +} > + > /** inany_equals - Compare two IPv[46] addresses > * @a, @b: IPv[46] addresses > * > @@ -295,5 +308,6 @@ static inline void inany_siphash_feed(struct siphash_state *state, > > const char *inany_ntop(const union inany_addr *src, char *dst, socklen_t size); > int inany_pton(const char *src, union inany_addr *dst); > +int inany_prefix_pton(char *src, union inany_addr *dst, int *prefix_len); > > #endif /* INANY_H */ > diff --git a/ip.c b/ip.c > index 9a7f4c5..40dc24e 100644 > --- a/ip.c > +++ b/ip.c > @@ -13,6 +13,8 @@ > */ > > #include > +#include > + > #include "util.h" > #include "ip.h" > > @@ -67,3 +69,22 @@ found: > *proto = nh; > return true; > } > + > +/** > + * ip4_class_prefix_len() - Get class based prefix length for IPv4 address > + * @addr: IPv4 address > + * > + * Return: prefix length based on address class, or 32 for other > + */ > +int ip4_class_prefix_len(const struct in_addr *addr) > +{ > + in_addr_t a = ntohl(addr->s_addr); > + > + if (IN_CLASSA(a)) > + return 32 - IN_CLASSA_NSHIFT; > + if (IN_CLASSB(a)) > + return 32 - IN_CLASSB_NSHIFT; > + if (IN_CLASSC(a)) > + return 32 - IN_CLASSC_NSHIFT; > + return 32; > +} > diff --git a/ip.h b/ip.h > index 5830b92..bd28640 100644 > --- a/ip.h > +++ b/ip.h > @@ -135,4 +135,6 @@ static const struct in_addr in4addr_broadcast = { 0xffffffff }; > #define IPV6_MIN_MTU 1280 > #endif > > +int ip4_class_prefix_len(const struct in_addr *addr); > + > #endif /* IP_H */ > diff --git a/passt.1 b/passt.1 > index db0d662..2c3eae9 100644 > --- a/passt.1 > +++ b/passt.1 > @@ -156,10 +156,14 @@ By default, the advertised MTU is 65520 bytes, that is, the maximum 802.3 MTU > minus the length of a 802.3 header, rounded to 32 bits (IPv4 words). > > .TP > -.BR \-a ", " \-\-address " " \fIaddr > +.BR \-a ", " \-\-address " " \fIaddr\fR[/\fIprefix_len\fR] > Assign IPv4 \fIaddr\fR via DHCP (\fByiaddr\fR), or \fIaddr\fR via DHCPv6 (option > 5) and an \fIaddr\fR-based prefix via NDP Router Advertisement (option type 3) > for an IPv6 \fIaddr\fR. > +An optional /\fIprefix_len\fR (0-32 for IPv4, 0-128 for IPv6) can be > +appended in CIDR notation (e.g. 192.0.2.1/24). This is an alternative to > +using the \fB-n\fR, \fB--netmask\fR option. Mixing CIDR notation with > +\fB-n\fR results in an error. > This option can be specified zero (for defaults) to two times (once for IPv4, > once for IPv6). > By default, assigned IPv4 and IPv6 addresses are taken from the host interfaces > @@ -172,10 +176,13 @@ is assigned for IPv4, and no additional address will be assigned for IPv6. > .TP > .BR \-n ", " \-\-netmask " " \fImask > Assign IPv4 netmask \fImask\fR, expressed as dot-decimal or number of bits, via > -DHCP (option 1). > -By default, the netmask associated to the host address matching the assigned one > -is used. If there's no matching address on the host, the netmask is determined > -according to the CIDR block of the assigned address (RFC 4632). > +DHCP (option 1). Alternatively, the prefix length can be specified using CIDR > +notation with the \fB-a\fR, \fB--address\fR option (e.g. \fB-a\fR 192.0.2.1/24). > +Mixing \fB-n\fR with CIDR notation results in an error. > +If no address is indicated, the netmask associated with the adopted host address, > +if any, is used. If an address is indicated, but without a prefix length, the > +netmask is determined based on the corresponding network class. In all other > +cases, the netmask is determined by using the indicated prefix length. > > .TP > .BR \-M ", " \-\-mac-addr " " \fIaddr > -- > 2.52.0 > -- 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