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annotate libtomcrypt/src/pk/asn1/der/bit/der_decode_raw_bit_string.c @ 1715:3974f087d9c0

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Disallow leading lines before the ident for server (#102) Per RFC4253 4.2 clients must be able to process other lines of data before the version string, server behavior is not defined neither with MUST/SHOULD nor with MAY. If server process up to 50 lines too - it may cause too long hanging session with invalid/evil client that consume host resources and potentially may lead to DDoS on poor embedded boxes. Let's require first line from client to be version string and fail early if it's not - matches both RFC and real OpenSSH behavior.
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Mon, 15 Jun 2020 18:22:18 +0500
parents 6dba84798cd5
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1471
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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
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2 *
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3 * LibTomCrypt is a library that provides various cryptographic
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4 * algorithms in a highly modular and flexible manner.
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5 *
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6 * The library is free for all purposes without any express
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7 * guarantee it works.
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8 */
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9 #include "tomcrypt.h"
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10
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11 /**
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12 @file der_decode_bit_string.c
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13 ASN.1 DER, encode a BIT STRING, Tom St Denis
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14 */
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15
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16
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17 #ifdef LTC_DER
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18
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19 #define SETBIT(v, n) (v=((unsigned char)(v) | (1U << (unsigned char)(n))))
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20 #define CLRBIT(v, n) (v=((unsigned char)(v) & ~(1U << (unsigned char)(n))))
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21
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22 /**
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23 Store a BIT STRING
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24 @param in The DER encoded BIT STRING
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25 @param inlen The size of the DER BIT STRING
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26 @param out [out] The array of bits stored (8 per char)
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27 @param outlen [in/out] The number of bits stored
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28 @return CRYPT_OK if successful
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29 */
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30 int der_decode_raw_bit_string(const unsigned char *in, unsigned long inlen,
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31 unsigned char *out, unsigned long *outlen)
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32 {
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33 unsigned long dlen, blen, x, y;
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34
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35 LTC_ARGCHK(in != NULL);
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36 LTC_ARGCHK(out != NULL);
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37 LTC_ARGCHK(outlen != NULL);
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38
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39 /* packet must be at least 4 bytes */
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40 if (inlen < 4) {
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41 return CRYPT_INVALID_ARG;
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42 }
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43
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44 /* check for 0x03 */
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45 if ((in[0]&0x1F) != 0x03) {
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46 return CRYPT_INVALID_PACKET;
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47 }
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48
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49 /* offset in the data */
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50 x = 1;
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51
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52 /* get the length of the data */
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53 if (in[x] & 0x80) {
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54 /* long format get number of length bytes */
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55 y = in[x++] & 0x7F;
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56
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57 /* invalid if 0 or > 2 */
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58 if (y == 0 || y > 2) {
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59 return CRYPT_INVALID_PACKET;
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60 }
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61
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62 /* read the data len */
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63 dlen = 0;
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64 while (y--) {
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65 dlen = (dlen << 8) | (unsigned long)in[x++];
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66 }
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67 } else {
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68 /* short format */
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69 dlen = in[x++] & 0x7F;
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70 }
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71
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72 /* is the data len too long or too short? */
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73 if ((dlen == 0) || (dlen + x > inlen)) {
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74 return CRYPT_INVALID_PACKET;
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75 }
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76
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77 /* get padding count */
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78 blen = ((dlen - 1) << 3) - (in[x++] & 7);
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79
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80 /* too many bits? */
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81 if (blen > *outlen) {
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82 *outlen = blen;
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83 return CRYPT_BUFFER_OVERFLOW;
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84 }
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85
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86 /* decode/store the bits */
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87 for (y = 0; y < blen; y++) {
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88 if (in[x] & (1 << (7 - (y & 7)))) {
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89 SETBIT(out[y/8], 7-(y%8));
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90 } else {
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91 CLRBIT(out[y/8], 7-(y%8));
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92 }
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93 if ((y & 7) == 7) {
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94 ++x;
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95 }
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96 }
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97
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98 /* we done */
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99 *outlen = blen;
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100 return CRYPT_OK;
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101 }
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102
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103 #endif
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104
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105 /* ref: $Format:%D$ */
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106 /* git commit: $Format:%H$ */
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107 /* commit time: $Format:%ai$ */