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dns: avoid truncation of searches list due to 256 char limit in glibc

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Before glibc 2.26, glibc's resolver would only honor 6 search entries
and a character limit of 256. This was lifted recently ([1], [2], [3]).

We also lift this limitation in NetworkManager ([4], [5]).

However, older glibc versions would just truncate the string at 255
characters. In particular, it would not only tuncate the list to 6
entries, but the entry which crosses the 256th character boundary would
be mangled. Avoid that, by adding spaces.

[1] https://sourceware.org/ml/libc-alpha/2017-08/msg00010.html
[2] https://sourceware.org/bugzilla/show_bug.cgi?id=19569
[3] https://sourceware.org/bugzilla/show_bug.cgi?id=21475
[4] https://gitlab.freedesktop.org/NetworkManager/NetworkManager/merge_requests/47
[5] https://gitlab.freedesktop.org/NetworkManager/NetworkManager/issues/80

(cherry picked from commit 49c11a44e4)
This commit is contained in:
Thomas Haller 2018-11-12 10:34:54 +01:00
parent b78a0ebcb1
commit dfce87b2b7
2 changed files with 31 additions and 2 deletions
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31
src/dns/nm-dns-manager.c
View file

@ -594,10 +594,39 @@ create_resolv_conf (const char *const*searches,
g_string_append (str, "# Generated by NetworkManager\n");
if (searches && searches[0]) {
gsize search_base_idx;
g_string_append (str, "search");
search_base_idx = str->len;
for (i = 0; searches[i]; i++) {
const char *s = searches[i];
gsize l = strlen (s);
if ( l == 0
|| NM_STRCHAR_ANY (s, ch, NM_IN_SET (ch, ' ', '\t', '\n'))) {
/* there should be no such characters in the search entry. Also,
* because glibc parser would treat them as line/word separator.
*
* Skip the value silently. */
continue;
}
if (search_base_idx > 0) {
if (str->len - search_base_idx + 1 + l > 254) {
/* this entry crosses the 256 character boundery. Older glibc versions
* would truncate the entry at this point.
*
* Fill the line with spaces to cross the 256 char boundary and continue
* afterwards. This way, the truncation happens between two search entries. */
while (str->len - search_base_idx < 257)
g_string_append_c (str, ' ');
search_base_idx = 0;
}
}
g_string_append_c (str, ' ');
g_string_append (str, searches[i]);
g_string_append_len (str, s, l);
}
g_string_append_c (str, '\n');
}

2
src/tests/test-general.c
View file

@ -1884,7 +1884,7 @@ test_dns_create_resolv_conf (void)
NULL,
NULL,
"# Generated by NetworkManager\n"
"search a2x456789.b2x456789.c2x456789.d2x456789.e2x456789.f2x456789.g2x456789.h2x456789.i2x456789.j2x4567890 a2y456789.b2y456789.c2y456789.d2y456789.e2y456789.f2y456789.g2y456789.h2y456789.i2y456789.j2y4567890 a2z456789.b2z456789.c2z456789.d2z456789.e2z456789.f2z456789.g2z456789.h2z456789.i2z456789.j2z4567890\n"
"search a2x456789.b2x456789.c2x456789.d2x456789.e2x456789.f2x456789.g2x456789.h2x456789.i2x456789.j2x4567890 a2y456789.b2y456789.c2y456789.d2y456789.e2y456789.f2y456789.g2y456789.h2y456789.i2y456789.j2y4567890 a2z456789.b2z456789.c2z456789.d2z456789.e2z456789.f2z456789.g2z456789.h2z456789.i2z456789.j2z4567890\n"
"");
}