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bece41ddb0
I thought I'd found all of these before, but perhaps a few managed to
slip in since I last looked. The character argument to the <ctype.h>
functions must have the value of an unsigned char or EOF; passing an
ordinary char (unless you know char is unsigned on every platform the
code will ever go near) risks mistaking '\xFF' for EOF, and causing
outright undefined behaviour on byte values in the range 80-FE. Never
do it.
(cherry picked from commit a76109c586)
122 lines
3.8 KiB
C
122 lines
3.8 KiB
C
/*
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* Validate a manual host key specification (either entered in the
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* GUI, or via -hostkey). If valid, we return true, and update 'key'
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* to contain a canonicalised version of the key string in 'key'
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* (which is guaranteed to take up at most as much space as the
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* original version), suitable for putting into the Conf. If not
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* valid, we return false.
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*/
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#include <string.h>
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#include <ctype.h>
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#include "putty.h"
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#include "misc.h"
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#define BASE64_CHARS_NOEQ \
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"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+/"
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#define BASE64_CHARS_ALL BASE64_CHARS_NOEQ "="
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bool validate_manual_hostkey(char *key)
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{
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char *p, *q, *r, *s;
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/*
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* Step through the string word by word, looking for a word that's
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* in one of the formats we like.
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*/
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p = key;
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while ((p += strspn(p, " \t"))[0]) {
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q = p;
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p += strcspn(p, " \t");
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if (*p) *p++ = '\0';
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/*
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* Now q is our word.
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*/
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if (strstartswith(q, "SHA256:")) {
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/* Test for a valid SHA256 key fingerprint. */
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r = q + 7;
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if (strspn(r, BASE64_CHARS_NOEQ) == 43) {
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memmove(key, q, 50); /* 7-char prefix + 43-char base64 */
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key[50] = '\0';
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return true;
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}
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}
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r = q;
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if (strstartswith(r, "MD5:"))
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r += 4;
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if (strlen(r) == 16*3 - 1 &&
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r[strspn(r, "0123456789abcdefABCDEF:")] == 0) {
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/*
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* Test for a valid MD5 key fingerprint. Check the colons
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* are in the right places, and if so, return the same
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* fingerprint canonicalised into lowercase.
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*/
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int i;
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for (i = 0; i < 16; i++)
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if (r[3*i] == ':' || r[3*i+1] == ':')
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goto not_fingerprint; /* sorry */
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for (i = 0; i < 15; i++)
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if (r[3*i+2] != ':')
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goto not_fingerprint; /* sorry */
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for (i = 0; i < 16*3 - 1; i++)
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key[i] = tolower((unsigned char)r[i]);
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key[16*3 - 1] = '\0';
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return true;
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}
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not_fingerprint:;
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/*
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* Before we check for a public-key blob, trim newlines out of
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* the middle of the word, in case someone's managed to paste
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* in a public-key blob _with_ them.
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*/
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for (r = s = q; *r; r++)
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if (*r != '\n' && *r != '\r')
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*s++ = *r;
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*s = '\0';
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if (strlen(q) % 4 == 0 && strlen(q) > 2*4 &&
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q[strspn(q, BASE64_CHARS_ALL)] == 0) {
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/*
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* Might be a base64-encoded SSH-2 public key blob. Check
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* that it starts with a sensible algorithm string. No
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* canonicalisation is necessary for this string type.
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*
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* The algorithm string must be at most 64 characters long
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* (RFC 4251 section 6).
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*/
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unsigned char decoded[6];
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unsigned alglen;
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int minlen;
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int len = 0;
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len += base64_decode_atom(q, decoded+len);
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if (len < 3)
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goto not_ssh2_blob; /* sorry */
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len += base64_decode_atom(q+4, decoded+len);
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if (len < 4)
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goto not_ssh2_blob; /* sorry */
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alglen = GET_32BIT_MSB_FIRST(decoded);
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if (alglen > 64)
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goto not_ssh2_blob; /* sorry */
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minlen = ((alglen + 4) + 2) / 3;
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if (strlen(q) < minlen)
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goto not_ssh2_blob; /* sorry */
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size_t base64_len = strspn(q, BASE64_CHARS_ALL);
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memmove(key, q, base64_len);
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key[base64_len] = '\0';
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return true;
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}
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not_ssh2_blob:;
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}
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return false;
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}
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