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Diffstat (limited to 'src/c-ares/ares_expand_name.c')
| -rw-r--r-- | src/c-ares/ares_expand_name.c | 205 |
1 files changed, 205 insertions, 0 deletions
diff --git a/src/c-ares/ares_expand_name.c b/src/c-ares/ares_expand_name.c new file mode 100644 index 000000000..738be8dcc --- /dev/null +++ b/src/c-ares/ares_expand_name.c @@ -0,0 +1,205 @@ + +/* Copyright 1998, 2011 by the Massachusetts Institute of Technology. + * + * Permission to use, copy, modify, and distribute this + * software and its documentation for any purpose and without + * fee is hereby granted, provided that the above copyright + * notice appear in all copies and that both that copyright + * notice and this permission notice appear in supporting + * documentation, and that the name of M.I.T. not be used in + * advertising or publicity pertaining to distribution of the + * software without specific, written prior permission. + * M.I.T. makes no representations about the suitability of + * this software for any purpose. It is provided "as is" + * without express or implied warranty. + */ + +#include "ares_setup.h" + +#ifdef HAVE_NETINET_IN_H +# include <netinet/in.h> +#endif +#ifdef HAVE_ARPA_NAMESER_H +# include <arpa/nameser.h> +#else +# include "nameser.h" +#endif +#ifdef HAVE_ARPA_NAMESER_COMPAT_H +# include <arpa/nameser_compat.h> +#endif + +#include "ares.h" +#include "ares_nowarn.h" +#include "ares_private.h" /* for the memdebug */ + +static int name_length(const unsigned char *encoded, const unsigned char *abuf, + int alen); + +/* Expand an RFC1035-encoded domain name given by encoded. The + * containing message is given by abuf and alen. The result given by + * *s, which is set to a NUL-terminated allocated buffer. *enclen is + * set to the length of the encoded name (not the length of the + * expanded name; the goal is to tell the caller how many bytes to + * move forward to get past the encoded name). + * + * In the simple case, an encoded name is a series of labels, each + * composed of a one-byte length (limited to values between 0 and 63 + * inclusive) followed by the label contents. The name is terminated + * by a zero-length label. + * + * In the more complicated case, a label may be terminated by an + * indirection pointer, specified by two bytes with the high bits of + * the first byte (corresponding to INDIR_MASK) set to 11. With the + * two high bits of the first byte stripped off, the indirection + * pointer gives an offset from the beginning of the containing + * message with more labels to decode. Indirection can happen an + * arbitrary number of times, so we have to detect loops. + * + * Since the expanded name uses '.' as a label separator, we use + * backslashes to escape periods or backslashes in the expanded name. + */ + +int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf, + int alen, char **s, long *enclen) +{ + int len, indir = 0; + char *q; + const unsigned char *p; + union { + ssize_t sig; + size_t uns; + } nlen; + + nlen.sig = name_length(encoded, abuf, alen); + if (nlen.sig < 0) + return ARES_EBADNAME; + + *s = ares_malloc(nlen.uns + 1); + if (!*s) + return ARES_ENOMEM; + q = *s; + + if (nlen.uns == 0) { + /* RFC2181 says this should be ".": the root of the DNS tree. + * Since this function strips trailing dots though, it becomes "" + */ + q[0] = '\0'; + + /* indirect root label (like 0xc0 0x0c) is 2 bytes long (stupid, but + valid) */ + if ((*encoded & INDIR_MASK) == INDIR_MASK) + *enclen = 2L; + else + *enclen = 1L; /* the caller should move one byte to get past this */ + + return ARES_SUCCESS; + } + + /* No error-checking necessary; it was all done by name_length(). */ + p = encoded; + while (*p) + { + if ((*p & INDIR_MASK) == INDIR_MASK) + { + if (!indir) + { + *enclen = aresx_uztosl(p + 2U - encoded); + indir = 1; + } + p = abuf + ((*p & ~INDIR_MASK) << 8 | *(p + 1)); + } + else + { + len = *p; + p++; + while (len--) + { + if (*p == '.' || *p == '\\') + *q++ = '\\'; + *q++ = *p; + p++; + } + *q++ = '.'; + } + } + if (!indir) + *enclen = aresx_uztosl(p + 1U - encoded); + + /* Nuke the trailing period if we wrote one. */ + if (q > *s) + *(q - 1) = 0; + else + *q = 0; /* zero terminate; LCOV_EXCL_LINE: empty names exit above */ + + return ARES_SUCCESS; +} + +/* Return the length of the expansion of an encoded domain name, or + * -1 if the encoding is invalid. + */ +static int name_length(const unsigned char *encoded, const unsigned char *abuf, + int alen) +{ + int n = 0, offset, indir = 0, top; + + /* Allow the caller to pass us abuf + alen and have us check for it. */ + if (encoded >= abuf + alen) + return -1; + + while (*encoded) + { + top = (*encoded & INDIR_MASK); + if (top == INDIR_MASK) + { + /* Check the offset and go there. */ + if (encoded + 1 >= abuf + alen) + return -1; + offset = (*encoded & ~INDIR_MASK) << 8 | *(encoded + 1); + if (offset >= alen) + return -1; + encoded = abuf + offset; + + /* If we've seen more indirects than the message length, + * then there's a loop. + */ + if (++indir > alen) + return -1; + } + else if (top == 0x00) + { + offset = *encoded; + if (encoded + offset + 1 >= abuf + alen) + return -1; + encoded++; + while (offset--) + { + n += (*encoded == '.' || *encoded == '\\') ? 2 : 1; + encoded++; + } + n++; + } + else + { + /* RFC 1035 4.1.4 says other options (01, 10) for top 2 + * bits are reserved. + */ + return -1; + } + } + + /* If there were any labels at all, then the number of dots is one + * less than the number of labels, so subtract one. + */ + return (n) ? n - 1 : n; +} + +/* Like ares_expand_name but returns EBADRESP in case of invalid input. */ +int ares__expand_name_for_response(const unsigned char *encoded, + const unsigned char *abuf, int alen, + char **s, long *enclen) +{ + int status = ares_expand_name(encoded, abuf, alen, s, enclen); + if (status == ARES_EBADNAME) + status = ARES_EBADRESP; + return status; +} |