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dns-domain: be more strict when encoding/decoding labels

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Labels of zero length are not OK, refuse them early on. The concept of a
"zero-length label" doesn't exist, a zero-length full domain name
however does (representing the root domain). See RFC 2181, Section 11.
This commit is contained in:
Lennart Poettering 2015-11-29 14:12:05 +01:00
parent bca27e1729
commit 3b37fa7352
3 changed files with 98 additions and 46 deletions
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139
src/shared/dns-domain.c
View File

@ -185,7 +185,11 @@ int dns_label_unescape_suffix(const char *name, const char **label_terminal, cha
int dns_label_escape(const char *p, size_t l, char *dest, size_t sz) {
char *q;
if (l > DNS_LABEL_MAX)
/* DNS labels must be between 1 and 63 characters long. A
* zero-length label does not exist. See RFC 2182, Section
* 11. */
if (l <= 0 || l > DNS_LABEL_MAX)
return -EINVAL;
if (sz < 1)
return -ENOSPC;
@ -198,10 +202,11 @@ int dns_label_escape(const char *p, size_t l, char *dest, size_t sz) {
if (*p == '.' || *p == '\\') {
/* Dot or backslash */
if (sz < 3)
return -ENOSPC;
/* Dot or backslash */
*(q++) = '\\';
*(q++) = *p;
@ -253,7 +258,7 @@ int dns_label_escape_new(const char *p, size_t l, char **ret) {
assert(p);
assert(ret);
if (l > DNS_LABEL_MAX)
if (l <= 0 || l > DNS_LABEL_MAX)
return -EINVAL;
s = new(char, DNS_LABEL_ESCAPED_MAX);
@ -273,32 +278,52 @@ int dns_label_escape_new(const char *p, size_t l, char **ret) {
int dns_label_apply_idna(const char *encoded, size_t encoded_size, char *decoded, size_t decoded_max) {
#ifdef HAVE_LIBIDN
_cleanup_free_ uint32_t *input = NULL;
size_t input_size;
size_t input_size, l;
const char *p;
bool contains_8bit = false;
char buffer[DNS_LABEL_MAX+1];
assert(encoded);
assert(decoded);
assert(decoded_max >= DNS_LABEL_MAX);
/* Converts an U-label into an A-label */
if (encoded_size <= 0)
return 0;
return -EINVAL;
for (p = encoded; p < encoded + encoded_size; p++)
if ((uint8_t) *p > 127)
contains_8bit = true;
if (!contains_8bit)
if (!contains_8bit) {
if (encoded_size > DNS_LABEL_MAX)
return -EINVAL;
return 0;
}
input = stringprep_utf8_to_ucs4(encoded, encoded_size, &input_size);
if (!input)
return -ENOMEM;
if (idna_to_ascii_4i(input, input_size, decoded, 0) != 0)
if (idna_to_ascii_4i(input, input_size, buffer, 0) != 0)
return -EINVAL;
return strlen(decoded);
l = strlen(buffer);
/* Verify that the the result is not longer than one DNS label. */
if (l <= 0 || l > DNS_LABEL_MAX)
return -EINVAL;
if (l > decoded_max)
return -ENOSPC;
memcpy(decoded, buffer, l);
/* If there's room, append a trailing NUL byte, but only then */
if (decoded_max > l)
decoded[l] = 0;
return (int) l;
#else
return 0;
#endif
@ -312,11 +337,14 @@ int dns_label_undo_idna(const char *encoded, size_t encoded_size, char *decoded,
uint32_t *output = NULL;
size_t w;
/* To be invoked after unescaping */
/* To be invoked after unescaping. Converts an A-label into an U-label. */
assert(encoded);
assert(decoded);
if (encoded_size <= 0 || encoded_size > DNS_LABEL_MAX)
return -EINVAL;
if (encoded_size < sizeof(IDNA_ACE_PREFIX)-1)
return 0;
@ -336,11 +364,16 @@ int dns_label_undo_idna(const char *encoded, size_t encoded_size, char *decoded,
if (!result)
return -ENOMEM;
if (w <= 0)
return 0;
if (w+1 > decoded_max)
return -EINVAL;
if (w > decoded_max)
return -ENOSPC;
memcpy(decoded, result, w);
/* Append trailing NUL byte if there's space, but only then. */
if (decoded_max > w)
decoded[w] = 0;
memcpy(decoded, result, w+1);
return w;
#else
return 0;
@ -511,24 +544,32 @@ int dns_name_equal(const char *x, const char *y) {
r = dns_label_unescape(&x, la, sizeof(la));
if (r < 0)
return r;
k = dns_label_undo_idna(la, r, la, sizeof(la));
if (k < 0)
return k;
if (k > 0)
r = k;
if (r > 0) {
k = dns_label_undo_idna(la, r, la, sizeof(la));
if (k < 0)
return k;
if (k > 0)
r = k;
}
q = dns_label_unescape(&y, lb, sizeof(lb));
if (q < 0)
return q;
w = dns_label_undo_idna(lb, q, lb, sizeof(lb));
if (w < 0)
return w;
if (w > 0)
q = w;
if (q > 0) {
w = dns_label_undo_idna(lb, q, lb, sizeof(lb));
if (w < 0)
return w;
if (w > 0)
q = w;
}
/* If one name had fewer labels than the other, this
* will show up as empty label here, which the
* strcasecmp() below will properly consider different
* from a non-empty label. */
la[r] = lb[q] = 0;
if (strcasecmp(la, lb))
if (strcasecmp(la, lb) != 0)
return false;
}
}
@ -549,11 +590,13 @@ int dns_name_endswith(const char *name, const char *suffix) {
r = dns_label_unescape(&n, ln, sizeof(ln));
if (r < 0)
return r;
k = dns_label_undo_idna(ln, r, ln, sizeof(ln));
if (k < 0)
return k;
if (k > 0)
r = k;
if (r > 0) {
k = dns_label_undo_idna(ln, r, ln, sizeof(ln));
if (k < 0)
return k;
if (k > 0)
r = k;
}
if (!saved_n)
saved_n = n;
@ -561,11 +604,13 @@ int dns_name_endswith(const char *name, const char *suffix) {
q = dns_label_unescape(&s, ls, sizeof(ls));
if (q < 0)
return q;
w = dns_label_undo_idna(ls, q, ls, sizeof(ls));
if (w < 0)
return w;
if (w > 0)
q = w;
if (q > 0) {
w = dns_label_undo_idna(ls, q, ls, sizeof(ls));
if (w < 0)
return w;
if (w > 0)
q = w;
}
if (r == 0 && q == 0)
return true;
@ -605,11 +650,13 @@ int dns_name_change_suffix(const char *name, const char *old_suffix, const char
r = dns_label_unescape(&n, ln, sizeof(ln));
if (r < 0)
return r;
k = dns_label_undo_idna(ln, r, ln, sizeof(ln));
if (k < 0)
return k;
if (k > 0)
r = k;
if (r > 0) {
k = dns_label_undo_idna(ln, r, ln, sizeof(ln));
if (k < 0)
return k;
if (k > 0)
r = k;
}
if (!saved_after)
saved_after = n;
@ -617,11 +664,13 @@ int dns_name_change_suffix(const char *name, const char *old_suffix, const char
q = dns_label_unescape(&s, ls, sizeof(ls));
if (q < 0)
return q;
w = dns_label_undo_idna(ls, q, ls, sizeof(ls));
if (w < 0)
return w;
if (w > 0)
q = w;
if (q > 0) {
w = dns_label_undo_idna(ls, q, ls, sizeof(ls));
if (w < 0)
return w;
if (w > 0)
q = w;
}
if (r == 0 && q == 0)
break;

3
src/shared/dns-domain.h
View File

@ -25,7 +25,10 @@
#include "hashmap.h"
#include "in-addr-util.h"
/* Length of a single label, with all escaping removed, excluding any trailing dot or NUL byte */
#define DNS_LABEL_MAX 63
/* Worst case length of a single label, with all escaping applied and room for a trailing NUL byte. */
#define DNS_LABEL_ESCAPED_MAX (DNS_LABEL_MAX*4+1)
int dns_label_unescape(const char **name, char *dest, size_t sz);

2
src/test/test-dns-domain.c
View File

@ -136,7 +136,7 @@ static void test_dns_label_escape_one(const char *what, size_t l, const char *ex
}
static void test_dns_label_escape(void) {
test_dns_label_escape_one("", 0, "", 0);
test_dns_label_escape_one("", 0, NULL, -EINVAL);
test_dns_label_escape_one("hallo", 5, "hallo", 5);
test_dns_label_escape_one("hallo", 6, NULL, -EINVAL);
test_dns_label_escape_one("hallo hallo.foobar,waldi", 24, "hallo\\032hallo\\.foobar\\044waldi", 31);