Add a "fork" of musl as //fusl.

fusl/src/network/lookup_name.c

+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+#include <net/if.h>
+#include <arpa/inet.h>
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <pthread.h>
+#include <errno.h>
+#include "lookup.h"
+#include "stdio_impl.h"
+#include "syscall.h"
+
+static int is_valid_hostname(const char *host)
+{
+        const unsigned char *s;
+        if (strnlen(host, 255)-1 >= 254 || mbstowcs(0, host, 0) == -1) return 0;
+        for (s=(void *)host; *s>=0x80 || *s=='.' || *s=='-' || isalnum(*s); s++);
+        return !*s;
+}
+
+static int name_from_null(struct address buf[static 2], const char *name, int family, int flags)
+{
+        int cnt = 0;
+        if (name) return 0;
+        if (flags & AI_PASSIVE) {
+                if (family != AF_INET6)
+                        buf[cnt++] = (struct address){ .family = AF_INET };
+                if (family != AF_INET)
+                        buf[cnt++] = (struct address){ .family = AF_INET6 };
+        } else {
+                if (family != AF_INET6)
+                        buf[cnt++] = (struct address){ .family = AF_INET, .addr = { 127,0,0,1 } };
+                if (family != AF_INET)
+                        buf[cnt++] = (struct address){ .family = AF_INET6, .addr = { [15] = 1 } };
+        }
+        return cnt;
+}
+
+static int name_from_numeric(struct address buf[static 1], const char *name, int family)
+{
+        return __lookup_ipliteral(buf, name, family);
+}
+
+static int name_from_hosts(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
+{
+        char line[512];
+        size_t l = strlen(name);
+        int cnt = 0;
+        unsigned char _buf[1032];
+        FILE _f, *f = __fopen_rb_ca("/etc/hosts", &_f, _buf, sizeof _buf);
+        if (!f) switch (errno) {
+        case ENOENT:
+        case ENOTDIR:
+        case EACCES:
+                return 0;
+        default:
+                return EAI_SYSTEM;
+        }
+        while (fgets(line, sizeof line, f) && cnt < MAXADDRS) {
+                char *p, *z;
+
+                if ((p=strchr(line, '#'))) *p++='\n', *p=0;
+                for(p=line+1; (p=strstr(p, name)) &&
+                        (!isspace(p[-1]) || !isspace(p[l])); p++);
+                if (!p) continue;
+
+                /* Isolate IP address to parse */
+                for (p=line; *p && !isspace(*p); p++);
+                *p++ = 0;
+                if (name_from_numeric(buf+cnt, line, family))
+                        cnt++;
+
+                /* Extract first name as canonical name */
+                for (; *p && isspace(*p); p++);
+                for (z=p; *z && !isspace(*z); z++);
+                *z = 0;
+                if (is_valid_hostname(p)) memcpy(canon, p, z-p+1);
+        }
+        __fclose_ca(f);
+        return cnt;
+}
+
+struct dpc_ctx {
+        struct address *addrs;
+        char *canon;
+        int cnt;
+};
+
+int __dns_parse(const unsigned char *, int, int (*)(void *, int, const void *, int, const void *), void *);
+int __dn_expand(const unsigned char *, const unsigned char *, const unsigned char *, char *, int);
+int __res_mkquery(int, const char *, int, int, const unsigned char *, int, const unsigned char*, unsigned char *, int);
+int __res_msend(int, const unsigned char *const *, const int *, unsigned char *const *, int *, int);
+
+#define RR_A 1
+#define RR_CNAME 5
+#define RR_AAAA 28
+
+static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet)
+{
+        char tmp[256];
+        struct dpc_ctx *ctx = c;
+        switch (rr) {
+        case RR_A:
+                if (len != 4) return -1;
+                ctx->addrs[ctx->cnt].family = AF_INET;
+                ctx->addrs[ctx->cnt].scopeid = 0;
+                memcpy(ctx->addrs[ctx->cnt++].addr, data, 4);
+                break;
+        case RR_AAAA:
+                if (len != 16) return -1;
+                ctx->addrs[ctx->cnt].family = AF_INET6;
+                ctx->addrs[ctx->cnt].scopeid = 0;
+                memcpy(ctx->addrs[ctx->cnt++].addr, data, 16);
+                break;
+        case RR_CNAME:
+                if (__dn_expand(packet, (const unsigned char *)packet + 512,
+                    data, tmp, sizeof tmp) > 0 && is_valid_hostname(tmp))
+                        strcpy(ctx->canon, tmp);
+                break;
+        }
+        return 0;
+}
+
+static int name_from_dns(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family)
+{
+        unsigned char qbuf[2][280], abuf[2][512];
+        const unsigned char *qp[2] = { qbuf[0], qbuf[1] };
+        unsigned char *ap[2] = { abuf[0], abuf[1] };
+        int qlens[2], alens[2];
+        int i, nq = 0;
+        struct dpc_ctx ctx = { .addrs = buf, .canon = canon };
+
+        if (family != AF_INET6) {
+                qlens[nq] = __res_mkquery(0, name, 1, RR_A, 0, 0, 0,
+                        qbuf[nq], sizeof *qbuf);
+                nq++;
+        }
+        if (family != AF_INET) {
+                qlens[nq] = __res_mkquery(0, name, 1, RR_AAAA, 0, 0, 0,
+                        qbuf[nq], sizeof *qbuf);
+                nq++;
+        }
+
+        if (__res_msend(nq, qp, qlens, ap, alens, sizeof *abuf) < 0) return EAI_SYSTEM;
+
+        for (i=0; i<nq; i++)
+                __dns_parse(abuf[i], alens[i], dns_parse_callback, &ctx);
+
+        if (ctx.cnt) return ctx.cnt;
+        if (alens[0] < 4 || (abuf[0][3] & 15) == 2) return EAI_AGAIN;
+        if ((abuf[0][3] & 15) == 3) return EAI_NONAME;
+        return EAI_FAIL;
+}
+
+static const struct policy {
+        unsigned char addr[16];
+        unsigned char len, mask;
+        unsigned char prec, label;
+} defpolicy[] = {
+        { "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\1", 15, 0xff, 50, 0 },
+        { "\0\0\0\0\0\0\0\0\0\0\xff\xff", 11, 0xff, 35, 4 },
+        { "\x20\2", 1, 0xff, 30, 2 },
+        { "\x20\1", 3, 0xff, 5, 5 },
+        { "\xfc", 0, 0xfe, 3, 13 },
+#if 0
+        /* These are deprecated and/or returned to the address
+         * pool, so despite the RFC, treating them as special
+         * is probably wrong. */
+        { "", 11, 0xff, 1, 3 },
+        { "\xfe\xc0", 1, 0xc0, 1, 11 },
+        { "\x3f\xfe", 1, 0xff, 1, 12 },
+#endif
+        /* Last rule must match all addresses to stop loop. */
+        { "", 0, 0, 40, 1 },
+};
+
+static const struct policy *policyof(const struct in6_addr *a)
+{
+        int i;
+        for (i=0; ; i++) {
+                if (memcmp(a->s6_addr, defpolicy[i].addr, defpolicy[i].len))
+                        continue;
+                if ((a->s6_addr[defpolicy[i].len] & defpolicy[i].mask)
+                    != defpolicy[i].addr[defpolicy[i].len])
+                        continue;
+                return defpolicy+i;
+        }
+}
+
+static int labelof(const struct in6_addr *a)
+{
+        return policyof(a)->label;
+}
+
+static int scopeof(const struct in6_addr *a)
+{
+        if (IN6_IS_ADDR_MULTICAST(a)) return a->s6_addr[1] & 15;
+        if (IN6_IS_ADDR_LINKLOCAL(a)) return 2;
+        if (IN6_IS_ADDR_LOOPBACK(a)) return 2;
+        if (IN6_IS_ADDR_SITELOCAL(a)) return 5;
+        return 14;
+}
+
+static int prefixmatch(const struct in6_addr *s, const struct in6_addr *d)
+{
+        /* FIXME: The common prefix length should be limited to no greater
+         * than the nominal length of the prefix portion of the source
+         * address. However the definition of the source prefix length is
+         * not clear and thus this limiting is not yet implemented. */
+        unsigned i;
+        for (i=0; i<128 && !((s->s6_addr[i/8]^d->s6_addr[i/8])&(128>>(i%8))); i++);
+        return i;
+}
+
+#define DAS_USABLE              0x40000000
+#define DAS_MATCHINGSCOPE       0x20000000
+#define DAS_MATCHINGLABEL       0x10000000
+#define DAS_PREC_SHIFT          20
+#define DAS_SCOPE_SHIFT         16
+#define DAS_PREFIX_SHIFT        8
+#define DAS_ORDER_SHIFT         0
+
+static int addrcmp(const void *_a, const void *_b)
+{
+        const struct address *a = _a, *b = _b;
+        return b->sortkey - a->sortkey;
+}
+
+int __lookup_name(struct address buf[static MAXADDRS], char canon[static 256], const char *name, int family, int flags)
+{
+        int cnt = 0, i, j;
+
+        *canon = 0;
+        if (name) {
+                /* reject empty name and check len so it fits into temp bufs */
+                size_t l = strnlen(name, 255);
+                if (l-1 >= 254)
+                        return EAI_NONAME;
+                memcpy(canon, name, l+1);
+        }
+
+        /* Procedurally, a request for v6 addresses with the v4-mapped
+         * flag set is like a request for unspecified family, followed
+         * by filtering of the results. */
+        if (flags & AI_V4MAPPED) {
+                if (family == AF_INET6) family = AF_UNSPEC;
+                else flags -= AI_V4MAPPED;
+        }
+
+        /* Try each backend until there's at least one result. */
+        cnt = name_from_null(buf, name, family, flags);
+        if (!cnt) cnt = name_from_numeric(buf, name, family);
+        if (!cnt && !(flags & AI_NUMERICHOST)) {
+                cnt = name_from_hosts(buf, canon, name, family);
+                if (!cnt) cnt = name_from_dns(buf, canon, name, family);
+        }
+        if (cnt<=0) return cnt ? cnt : EAI_NONAME;
+
+        /* Filter/transform results for v4-mapped lookup, if requested. */
+        if (flags & AI_V4MAPPED) {
+                if (!(flags & AI_ALL)) {
+                        /* If any v6 results exist, remove v4 results. */
+                        for (i=0; i<cnt && buf[i].family != AF_INET6; i++);
+                        if (i<cnt) {
+                                for (j=0; i<cnt; i++) {
+                                        if (buf[i].family == AF_INET6)
+                                                buf[j++] = buf[i];
+                                }
+                                cnt = i = j;
+                        }
+                }
+                /* Translate any remaining v4 results to v6 */
+                for (i=0; i<cnt; i++) {
+                        if (buf[i].family != AF_INET) continue;
+                        memcpy(buf[i].addr+12, buf[i].addr, 4);
+                        memcpy(buf[i].addr, "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
+                        buf[i].family = AF_INET6;
+                }
+        }
+
+        /* No further processing is needed if there are fewer than 2
+         * results or if there are only IPv4 results. */
+        if (cnt<2 || family==AF_INET) return cnt;
+        for (i=0; buf[i].family == AF_INET; i++)
+                if (i==cnt) return cnt;
+
+        int cs;
+        pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+
+        /* The following implements a subset of RFC 3484/6724 destination
+         * address selection by generating a single 31-bit sort key for
+         * each address. Rules 3, 4, and 7 are omitted for having
+         * excessive runtime and code size cost and dubious benefit.
+         * So far the label/precedence table cannot be customized. */
+        for (i=0; i<cnt; i++) {
+                int key = 0;
+                struct sockaddr_in6 sa, da = {
+                        .sin6_family = AF_INET6,
+                        .sin6_scope_id = buf[i].scopeid,
+                        .sin6_port = 65535
+                };
+                if (buf[i].family == AF_INET6) {
+                        memcpy(da.sin6_addr.s6_addr, buf[i].addr, 16);
+                } else {
+                        memcpy(da.sin6_addr.s6_addr,
+                                "\0\0\0\0\0\0\0\0\0\0\xff\xff", 12);
+                        memcpy(da.sin6_addr.s6_addr+12, buf[i].addr, 4);
+                }
+                const struct policy *dpolicy = policyof(&da.sin6_addr);
+                int dscope = scopeof(&da.sin6_addr);
+                int dlabel = dpolicy->label;
+                int dprec = dpolicy->prec;
+                int prefixlen = 0;
+                int fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_UDP);
+                if (fd >= 0) {
+                        if (!connect(fd, (void *)&da, sizeof da)) {
+                                key |= DAS_USABLE;
+                                if (!getsockname(fd, (void *)&sa,
+                                    &(socklen_t){sizeof sa})) {
+                                        if (dscope == scopeof(&sa.sin6_addr))
+                                                key |= DAS_MATCHINGSCOPE;
+                                        if (dlabel == labelof(&sa.sin6_addr))
+                                                key |= DAS_MATCHINGLABEL;
+                                        prefixlen = prefixmatch(&sa.sin6_addr,
+                                                &da.sin6_addr);
+                                }
+                        }
+                        close(fd);
+                }
+                key |= dprec << DAS_PREC_SHIFT;
+                key |= (15-dscope) << DAS_SCOPE_SHIFT;
+                key |= prefixlen << DAS_PREFIX_SHIFT;
+                key |= (MAXADDRS-i) << DAS_ORDER_SHIFT;
+                buf[i].sortkey = key;
+        }
+        qsort(buf, cnt, sizeof *buf, addrcmp);
+
+        pthread_setcancelstate(cs, 0);
+
+        return cnt;
+}