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Fix binary search on lists of 0 or 1 element.

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The implementation we added has a tendency to crash with lists of 0 or
one element.  That can happen if we get a consensus vote, v2
consensus, consensus, or geoip file with 0 or 1 element.  There's a
DOS opportunity there that authorities could exploit against one
another, and which an evil v2 authority could exploit against anything
downloading v2 directory information..

This fix is minimalistic: It just adds a special-case for 0- and
1-element lists.  For 0.2.4 (the current alpha series) we'll want a
better patch.

This is bug 7191; it's a fix on 0.2.0.10-alpha.
This commit is contained in:
Nick Mathewson 2012-10-23 17:12:37 -04:00
parent 8743080a28
commit 8905789170
1 changed files with 22 additions and 1 deletions
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23
src/common/container.c
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@ -572,7 +572,28 @@ smartlist_bsearch_idx(const smartlist_t *sl, const void *key,
int (*compare)(const void *key, const void **member),
int *found_out)
{
int hi = smartlist_len(sl) - 1, lo = 0, cmp, mid;
const int len = smartlist_len(sl);
int hi, lo, cmp, mid;
if (len == 0) {
*found_out = 0;
return 0;
} else if (len == 1) {
cmp = compare(key, (const void **) &sl->list[0]);
if (cmp == 0) {
*found_out = 1;
return 0;
} else if (cmp < 0) {
*found_out = 0;
return 0;
} else {
*found_out = 0;
return 1;
}
}
hi = smartlist_len(sl) - 1;
lo = 0;
while (lo <= hi) {
mid = (lo + hi) / 2;