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Prevent int underflow in dirvote.c compare_vote_rs_.

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This should be "impossible" without making a SHA1 collision, but
let's not keep the assumption that SHA1 collisions are super-hard.

This prevents another case related to 21278.  There should be no
behavioral change unless -ftrapv is on.
This commit is contained in:
Nick Mathewson 2017-02-13 14:07:35 -05:00
parent 1afc2ed956
commit a0ef3cf088
1 changed files with 22 additions and 8 deletions
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30
src/or/dirvote.c
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@ -421,16 +421,30 @@ compare_vote_rs(const vote_routerstatus_t *a, const vote_routerstatus_t *b)
b->status.descriptor_digest,
DIGEST_LEN)))
return r;
if ((r = (int)(b->status.published_on - a->status.published_on)))
return r;
/* If we actually reached this point, then the identities and
* the descriptor digests matched, so somebody is making SHA1 collisions.
*/
#define CMP_FIELD(utype, itype, field) do { \
utype aval = (utype) (itype) a->status.field; \
utype bval = (utype) (itype) b->status.field; \
utype u = bval - aval; \
itype r2 = (itype) u; \
if (r2 < 0) { \
return -1; \
} else if (r2 > 0) { \
return 1; \
} \
} while (0)
CMP_FIELD(uint64_t, int64_t, published_on);
if ((r = strcmp(b->status.nickname, a->status.nickname)))
return r;
if ((r = (((int)b->status.addr) - ((int)a->status.addr))))
return r;
if ((r = (((int)b->status.or_port) - ((int)a->status.or_port))))
return r;
if ((r = (((int)b->status.dir_port) - ((int)a->status.dir_port))))
return r;
CMP_FIELD(unsigned, int, addr);
CMP_FIELD(unsigned, int, or_port);
CMP_FIELD(unsigned, int, dir_port);
return 0;
}