On Thu, Dec 18, 2025 at 05:22:12PM -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.

Add conf_addr_prefix_len() helper function that: - Parses address strings with optional /prefix_len suffix using inany_pton() - Validates prefix length based on address family (0-32 for IPv4, 0-128 for IPv6) - Returns address family via union inany_addr output parameter

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 --- conf.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 79 insertions(+), 15 deletions(-)

diff --git a/conf.c b/conf.c index 2942c8c..81a6ca3 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; } @@ -690,6 +690,50 @@ static int conf_ip4_prefix(const char *arg) return len; }

+/** + * conf_addr_prefix_len() - Parse address with optional prefix length + * @arg: Address string, optionally with /prefix_len suffix (modified) + * @addr: Output for parsed address + * @prefix_len: Output for prefix length (0 if not specified)

This makes me slightly nervous, because a 0-length prefix is theoretically valid. Telling the guest that the entire internet is on it's LAN is pretty weird, but it does potentially have a use: it means the guest can reach the world without having a default gateway (at the cost of requiring many ARP entries in the guest).

+ * + * Return: AF_INET for IPv4, AF_INET6 for IPv6, -1 on error + */ +static int conf_addr_prefix_len(char *arg, union inany_addr *addr, + int *prefix_len) +{ + char *slash; + + *prefix_len = 0; + + /* Check for /prefix_len suffix */ + slash = strchr(arg, '/'); + if (slash) { + unsigned long len; + char *end; + + *slash = '\0'; + errno = 0; + len = strtoul(slash + 1, &end, 10); + if (errno || *end) + return -1; + + *prefix_len = len; + } + + if (!inany_pton(arg, addr)) + return -1; + + if (inany_v4(addr)) { + if (*prefix_len > 32) + return -1; + return AF_INET;

Ah... sorry.. I just realised there's a subtle problem using inany_pton() here. The above is correct if the user entered an IPv4 address. However, it's possible they could have explicitly entered a v4-mapped IPv6 address. inany_pton() will interpret that like a an IPv4 address, which I think is correct, *except* that ::ffff:192.168.1.1/112 should be interpreted like: 192.168.1.1/16 not like: 192.168.1.1/112 Maybe we actually want to create an inany_prefix_pton() or something.

+ } + + if (*prefix_len > 128) + return -1; + return AF_INET6; +} + /** * conf_ip4() - Verify or detect IPv4 support, get relevant addresses * @ifi: Host interface to attempt (0 to determine one) @@ -896,7 +940,7 @@ 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" @@ -1499,6 +1543,7 @@ void conf(struct ctx *c, int argc, char **argv) const char *logname = (c->mode == MODE_PASTA) ? "pasta" : "passt"; char userns[PATH_MAX] = { 0 }, netns[PATH_MAX] = { 0 }; bool copy_addrs_opt = false, copy_routes_opt = false; + bool prefix_from_cidr = false, prefix_from_opt = false; enum fwd_ports_mode fwd_default = FWD_NONE; bool v4_only = false, v6_only = false; unsigned dns4_idx = 0, dns6_idx = 0; @@ -1808,23 +1853,39 @@ 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)) { + case 'a': { + union inany_addr addr; + const struct in_addr *a4; + int prefix_len = 0; + int af; + + af = conf_addr_prefix_len(optarg, &addr, &prefix_len); + + if (af == AF_INET6 && + !IN6_IS_ADDR_UNSPECIFIED(&addr.a6) && + !IN6_IS_ADDR_LOOPBACK(&addr.a6) && + !IN6_IS_ADDR_V4MAPPED(&addr.a6) &&

The V4MAPPED test is no longer relevant, since if it was true, conf_addr_prefix_len() could not return AF_INET6.

+ !IN6_IS_ADDR_V4COMPAT(&addr.a6) && + !IN6_IS_ADDR_MULTICAST(&addr.a6)) { + c->ip6.addr = addr.a6; if (c->mode == MODE_PASTA) c->ip6.no_copy_addrs = true; break; }

Note that we do have inany_is_unicast(), inany_is_loopback() and inany_is_unspecified() helpers that might allow us to simplify this.

- 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)) { + a4 = inany_v4(&addr); + if (af == AF_INET && a4 && + !IN4_IS_ADDR_UNSPECIFIED(a4) && + !IN4_IS_ADDR_BROADCAST(a4) && + !IN4_IS_ADDR_LOOPBACK(a4) && + !IN4_IS_ADDR_MULTICAST(a4)) { + c->ip4.addr = *a4; + if (prefix_len) { + if (prefix_from_opt) + die("Can't use both -n and CIDR prefix length"); + c->ip4.prefix_len = prefix_len; + prefix_from_cidr = true; + } if (c->mode == MODE_PASTA) c->ip4.no_copy_addrs = true; break; @@ -1832,11 +1893,14 @@ void conf(struct ctx *c, int argc, char **argv)

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); -- 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