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libmp: fix mpmod() aliasing bug when n == r and x < 0 (thanks aiju, mischief)

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mischief found this in rsafill()'s call mpmod(c2, x, x), where
d parameter is negative (rsagen created a rsa key with negative dk).
This commit is contained in:
cinap_lenrek 2017-02-05 02:48:13 +01:00
parent 7f12431009
commit 96769e0476
1 changed files with 6 additions and 2 deletions
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8
sys/src/libmp/port/mpmod.c
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@ -6,11 +6,15 @@ void
mpmod(mpint *x, mpint *n, mpint *r)
{
int sign;
mpint *ns;
sign = x->sign;
ns = sign < 0 && n == r ? mpcopy(n) : n;
if((n->flags & MPfield) == 0
|| ((Mfield*)n)->reduce((Mfield*)n, x, r) != 0)
mpdiv(x, n, nil, r);
if(sign < 0)
mpmagsub(n, r, r);
if(sign < 0){
mpmagsub(ns, r, r);
if(ns != n) mpfree(ns);
}
}