Mercurial > dropbear
annotate libtommath/bn_mp_exptmod.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> |
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date | Mon, 09 Jul 2018 16:27:53 +0200 |
parents | 1051e4eea25a |
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rev | line source |
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1 #include "tommath_private.h" |
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2 #ifdef BN_MP_EXPTMOD_C |
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */ |
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4 /* SPDX-License-Identifier: Unlicense */ |
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5 |
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6 /* this is a shell function that calls either the normal or Montgomery |
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7 * exptmod functions. Originally the call to the montgomery code was |
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8 * embedded in the normal function but that wasted alot of stack space |
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9 * for nothing (since 99% of the time the Montgomery code would be called) |
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10 */ |
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11 mp_err mp_exptmod(const mp_int *G, const mp_int *X, const mp_int *P, mp_int *Y) |
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12 { |
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13 int dr; |
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14 |
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15 /* modulus P must be positive */ |
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16 if (P->sign == MP_NEG) { |
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17 return MP_VAL; |
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18 } |
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19 |
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20 /* if exponent X is negative we have to recurse */ |
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21 if (X->sign == MP_NEG) { |
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22 mp_int tmpG, tmpX; |
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23 mp_err err; |
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24 |
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25 if (!MP_HAS(MP_INVMOD)) { |
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26 return MP_VAL; |
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27 } |
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28 |
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29 if ((err = mp_init_multi(&tmpG, &tmpX, NULL)) != MP_OKAY) { |
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30 return err; |
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31 } |
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32 |
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33 /* first compute 1/G mod P */ |
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34 if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) { |
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35 goto LBL_ERR; |
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36 } |
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37 |
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38 /* now get |X| */ |
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39 if ((err = mp_abs(X, &tmpX)) != MP_OKAY) { |
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40 goto LBL_ERR; |
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41 } |
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42 |
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43 /* and now compute (1/G)**|X| instead of G**X [X < 0] */ |
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44 err = mp_exptmod(&tmpG, &tmpX, P, Y); |
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45 LBL_ERR: |
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46 mp_clear_multi(&tmpG, &tmpX, NULL); |
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47 return err; |
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48 } |
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49 |
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50 /* modified diminished radix reduction */ |
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51 if (MP_HAS(MP_REDUCE_IS_2K_L) && MP_HAS(MP_REDUCE_2K_L) && MP_HAS(S_MP_EXPTMOD) && |
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52 (mp_reduce_is_2k_l(P) == MP_YES)) { |
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53 return s_mp_exptmod(G, X, P, Y, 1); |
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54 } |
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55 |
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56 /* is it a DR modulus? default to no */ |
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57 dr = (MP_HAS(MP_DR_IS_MODULUS) && (mp_dr_is_modulus(P) == MP_YES)) ? 1 : 0; |
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58 |
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59 /* if not, is it a unrestricted DR modulus? */ |
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60 if (MP_HAS(MP_REDUCE_IS_2K) && (dr == 0)) { |
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61 dr = (mp_reduce_is_2k(P) == MP_YES) ? 2 : 0; |
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62 } |
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63 |
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64 /* if the modulus is odd or dr != 0 use the montgomery method */ |
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65 if (MP_HAS(S_MP_EXPTMOD_FAST) && (MP_IS_ODD(P) || (dr != 0))) { |
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66 return s_mp_exptmod_fast(G, X, P, Y, dr); |
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67 } else if (MP_HAS(S_MP_EXPTMOD)) { |
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68 /* otherwise use the generic Barrett reduction technique */ |
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69 return s_mp_exptmod(G, X, P, Y, 0); |
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70 } else { |
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71 /* no exptmod for evens */ |
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72 return MP_VAL; |
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73 } |
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74 } |
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75 |
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76 #endif |