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annotate sk-ed25519.c @ 1930:299f4f19ba19

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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 333688ec53d0
children
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1 #include "includes.h"
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2
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3 #if DROPBEAR_SK_ED25519
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4
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5 #include "dbutil.h"
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6 #include "buffer.h"
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7 #include "curve25519.h"
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8 #include "ed25519.h"
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9 #include "ssh.h"
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11 int buf_sk_ed25519_verify(buffer *buf, const dropbear_ed25519_key *key, const buffer *data_buf, const char* app, unsigned int applen) {
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12
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13 int ret = DROPBEAR_FAILURE;
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14 unsigned char *s;
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15 unsigned long slen;
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16 hash_state hs;
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17 unsigned char hash[SHA256_HASH_SIZE];
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18 buffer *sk_buffer = NULL;
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19 unsigned char flags;
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20 unsigned int counter;
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22 TRACE(("enter buf_sk_ed25519_verify"))
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23 dropbear_assert(key != NULL);
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25 slen = buf_getint(buf);
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26 if (slen != 64 || buf->len - buf->pos < slen) {
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27 TRACE(("leave buf_sk_ed25519_verify: bad size"))
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28 goto out;
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29 }
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30 s = buf_getptr(buf, slen);
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31 buf_incrpos(buf, slen);
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32
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33 flags = buf_getbyte (buf);
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34 counter = buf_getint (buf);
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35 /* create the message to be signed */
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36 sk_buffer = buf_new (2*SHA256_HASH_SIZE+5);
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37 sha256_init (&hs);
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38 sha256_process (&hs, app, applen);
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39 sha256_done (&hs, hash);
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40 buf_putbytes (sk_buffer, hash, sizeof (hash));
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41 buf_putbyte (sk_buffer, flags);
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42 buf_putint (sk_buffer, counter);
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43 sha256_init (&hs);
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44 sha256_process (&hs, data_buf->data, data_buf->len);
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45 sha256_done (&hs, hash);
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46 buf_putbytes (sk_buffer, hash, sizeof (hash));
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47
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48 if (dropbear_ed25519_verify(sk_buffer->data, sk_buffer->len,
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49 s, slen, key->pub) == 0) {
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50 /* signature is valid */
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51 TRACE(("leave buf_sk_ed25519_verify: success!"))
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52 ret = DROPBEAR_SUCCESS;
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53 }
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54
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55 /* TODO: allow "no-touch-required" or "verify-required" authorized_keys options */
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56 if (!(flags & SSH_SK_USER_PRESENCE_REQD)) {
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57 if (ret == DROPBEAR_SUCCESS) {
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58 dropbear_log(LOG_WARNING, "Rejecting, user-presence not set");
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59 }
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60 ret = DROPBEAR_FAILURE;
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61 }
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62 out:
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63 buf_free(sk_buffer);
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64 TRACE(("leave buf_sk_ed25519_verify: ret %d", ret))
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65 return ret;
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66 }
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68 #endif /* DROPBEAR_SK_ED25519 */