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Fix bug in 6860cf932b

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The optimisation based on the assumption that
"try now points to the last domain that sorts before the query"
fails in the specific edge case that the query sorts before
_any_ of the server domains. Handle this case.

Thanks to Xingcong Li for finding a test case for this bug.
This commit is contained in:
Simon Kelley
2021-06-20 22:57:54 +01:00
parent d0ae3f5a4d
commit a0a3b8ad3e
1 changed files with 26 additions and 22 deletions
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46
src/domain-match.c
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@@ -133,7 +133,32 @@ int lookup_domain(char *qdomain, int flags, int *lowout, int *highout)
else else
{ {
if (low == try) if (low == try)
{
/* try now points to the last domain that sorts before the query, so
we know that a substring of the query shorter than it is required to match, so
find the largest domain that's shorter than try. Note that just going to
try+1 is not optimal, consider searching bbb in (aaa,ccc,bb). try will point
to aaa, since ccc sorts after bbb, but the first domain that has a chance to
match is bb. So find the length of the first domain later than try which is
is shorter than it.
There's a nasty edge case when qdomain sorts before _any_ of the
server domains, where try _doesn't point_ to the last domain that sorts
before the query, since no such domain exists. In that case, the loop
exits via the rc < 0 && high == try path above and this code is
not executed. */
ssize_t len, old = daemon->serverarray[try]->domain_len;
while (++try != daemon->serverarraysz)
{
if (old != (len = daemon->serverarray[try]->domain_len))
{
/* crop_query must be at least one always. */
if (qlen != len)
crop_query = qlen - len;
break; break;
}
}
break;
}
low = try; low = try;
} }
}; };
@@ -153,27 +178,6 @@ int lookup_domain(char *qdomain, int flags, int *lowout, int *highout)
break; break;
} }
} }
else
{
/* try now points to the last domain that sorts before the query, so
we know that a substring of the query shorter than it is required to match, so
find the largest domain that's shorter than try. Note that just going to
try+1 is not optimal, consider searching bbb in (aaa,ccc,bb). try will point
to aaa, since ccc sorts after bbb, but the first domain that has a chance to
match is dd. So find the length of the first domain later than try which is
is shorter than it. */
ssize_t len, old = daemon->serverarray[try]->domain_len;
while (++try != daemon->serverarraysz)
{
if (old != (len = daemon->serverarray[try]->domain_len))
{
/* crop_query must be at least one always. */
if (qlen != len)
crop_query = qlen - len;
break;
}
}
}
qlen -= crop_query; qlen -= crop_query;
if (leading_dot) if (leading_dot)