Mercurial > dropbear
view libtommath/bn_s_mp_invmod_slow.c @ 1930:299f4f19ba19
Add /usr/sbin and /sbin to default root PATH
When dropbear is used in a very restricted environment (such as in a
initrd), the default user shell is often also very restricted
and doesn't take care of setting the PATH so the user ends up
with the PATH set by dropbear. Unfortunately, dropbear always
sets "/usr/bin:/bin" as default PATH even for the root user
which should have /usr/sbin and /sbin too.
For a concrete instance of this problem, see the "Remote Unlocking"
section in this tutorial: https://paxswill.com/blog/2013/11/04/encrypted-raspberry-pi/
It speaks of a bug in the initramfs script because it's written "blkid"
instead of "/sbin/blkid"... this is just because the scripts from the
initramfs do not expect to have a PATH without the sbin directories and
because dropbear is not setting the PATH appropriately for the root user.
I'm thus suggesting to use the attached patch to fix this misbehaviour (I
did not test it, but it's easy enough). It might seem anecdotic but
multiple Kali users have been bitten by this.
From https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=903403
author | Raphael Hertzog <hertzog@debian.org> |
---|---|
date | Mon, 09 Jul 2018 16:27:53 +0200 |
parents | 1051e4eea25a |
children |
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#include "tommath_private.h" #ifdef BN_S_MP_INVMOD_SLOW_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ /* hac 14.61, pp608 */ mp_err s_mp_invmod_slow(const mp_int *a, const mp_int *b, mp_int *c) { mp_int x, y, u, v, A, B, C, D; mp_err err; /* b cannot be negative */ if ((b->sign == MP_NEG) || MP_IS_ZERO(b)) { return MP_VAL; } /* init temps */ if ((err = mp_init_multi(&x, &y, &u, &v, &A, &B, &C, &D, NULL)) != MP_OKAY) { return err; } /* x = a, y = b */ if ((err = mp_mod(a, b, &x)) != MP_OKAY) goto LBL_ERR; if ((err = mp_copy(b, &y)) != MP_OKAY) goto LBL_ERR; /* 2. [modified] if x,y are both even then return an error! */ if (MP_IS_EVEN(&x) && MP_IS_EVEN(&y)) { err = MP_VAL; goto LBL_ERR; } /* 3. u=x, v=y, A=1, B=0, C=0,D=1 */ if ((err = mp_copy(&x, &u)) != MP_OKAY) goto LBL_ERR; if ((err = mp_copy(&y, &v)) != MP_OKAY) goto LBL_ERR; mp_set(&A, 1uL); mp_set(&D, 1uL); top: /* 4. while u is even do */ while (MP_IS_EVEN(&u)) { /* 4.1 u = u/2 */ if ((err = mp_div_2(&u, &u)) != MP_OKAY) goto LBL_ERR; /* 4.2 if A or B is odd then */ if (MP_IS_ODD(&A) || MP_IS_ODD(&B)) { /* A = (A+y)/2, B = (B-x)/2 */ if ((err = mp_add(&A, &y, &A)) != MP_OKAY) goto LBL_ERR; if ((err = mp_sub(&B, &x, &B)) != MP_OKAY) goto LBL_ERR; } /* A = A/2, B = B/2 */ if ((err = mp_div_2(&A, &A)) != MP_OKAY) goto LBL_ERR; if ((err = mp_div_2(&B, &B)) != MP_OKAY) goto LBL_ERR; } /* 5. while v is even do */ while (MP_IS_EVEN(&v)) { /* 5.1 v = v/2 */ if ((err = mp_div_2(&v, &v)) != MP_OKAY) goto LBL_ERR; /* 5.2 if C or D is odd then */ if (MP_IS_ODD(&C) || MP_IS_ODD(&D)) { /* C = (C+y)/2, D = (D-x)/2 */ if ((err = mp_add(&C, &y, &C)) != MP_OKAY) goto LBL_ERR; if ((err = mp_sub(&D, &x, &D)) != MP_OKAY) goto LBL_ERR; } /* C = C/2, D = D/2 */ if ((err = mp_div_2(&C, &C)) != MP_OKAY) goto LBL_ERR; if ((err = mp_div_2(&D, &D)) != MP_OKAY) goto LBL_ERR; } /* 6. if u >= v then */ if (mp_cmp(&u, &v) != MP_LT) { /* u = u - v, A = A - C, B = B - D */ if ((err = mp_sub(&u, &v, &u)) != MP_OKAY) goto LBL_ERR; if ((err = mp_sub(&A, &C, &A)) != MP_OKAY) goto LBL_ERR; if ((err = mp_sub(&B, &D, &B)) != MP_OKAY) goto LBL_ERR; } else { /* v - v - u, C = C - A, D = D - B */ if ((err = mp_sub(&v, &u, &v)) != MP_OKAY) goto LBL_ERR; if ((err = mp_sub(&C, &A, &C)) != MP_OKAY) goto LBL_ERR; if ((err = mp_sub(&D, &B, &D)) != MP_OKAY) goto LBL_ERR; } /* if not zero goto step 4 */ if (!MP_IS_ZERO(&u)) { goto top; } /* now a = C, b = D, gcd == g*v */ /* if v != 1 then there is no inverse */ if (mp_cmp_d(&v, 1uL) != MP_EQ) { err = MP_VAL; goto LBL_ERR; } /* if its too low */ while (mp_cmp_d(&C, 0uL) == MP_LT) { if ((err = mp_add(&C, b, &C)) != MP_OKAY) goto LBL_ERR; } /* too big */ while (mp_cmp_mag(&C, b) != MP_LT) { if ((err = mp_sub(&C, b, &C)) != MP_OKAY) goto LBL_ERR; } /* C is now the inverse */ mp_exch(&C, c); err = MP_OKAY; LBL_ERR: mp_clear_multi(&x, &y, &u, &v, &A, &B, &C, &D, NULL); return err; } #endif