Initial revision

1 files changed, 478 insertions, 0 deletions

diff --git a/auth-rsa.c b/auth-rsa.c
new file mode 100644
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--- /dev/null
+++ b/auth-rsa.c
@@ -0,0 +1,478 @@
+/*
+
+auth-rsa.c
+
+Author: Tatu Ylonen <ylo@cs.hut.fi>
+
+Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+                   All rights reserved
+
+Created: Mon Mar 27 01:46:52 1995 ylo
+
+RSA-based authentication.  This code determines whether to admit a login
+based on RSA authentication.  This file also contains functions to check
+validity of the host key.
+
+*/
+
+#include "includes.h"
+RCSID("$Id: auth-rsa.c,v 1.1 1999/10/27 03:42:43 damien Exp $");
+
+#include "rsa.h"
+#include "packet.h"
+#include "xmalloc.h"
+#include "ssh.h"
+#include "mpaux.h"
+#include "uidswap.h"
+
+#include <openssl/rsa.h>
+#include <openssl/md5.h>
+
+/* Flags that may be set in authorized_keys options. */
+extern int no_port_forwarding_flag;
+extern int no_agent_forwarding_flag;
+extern int no_x11_forwarding_flag;
+extern int no_pty_flag;
+extern char *forced_command;
+extern struct envstring *custom_environment;
+
+/* Session identifier that is used to bind key exchange and authentication
+   responses to a particular session. */
+extern unsigned char session_id[16];
+
+/* The .ssh/authorized_keys file contains public keys, one per line, in the
+   following format:
+     options bits e n comment
+   where bits, e and n are decimal numbers, 
+   and comment is any string of characters up to newline.  The maximum
+   length of a line is 8000 characters.  See the documentation for a
+   description of the options.
+*/
+
+/* Performs the RSA authentication challenge-response dialog with the client,
+   and returns true (non-zero) if the client gave the correct answer to
+   our challenge; returns zero if the client gives a wrong answer. */
+
+int
+auth_rsa_challenge_dialog(unsigned int bits, BIGNUM *e, BIGNUM *n)
+{
+  BIGNUM *challenge, *encrypted_challenge, *aux;
+  RSA *pk;
+  BN_CTX *ctx = BN_CTX_new();
+  unsigned char buf[32], mdbuf[16], response[16];
+  MD5_CTX md;
+  unsigned int i;
+  int plen, len;
+
+  encrypted_challenge = BN_new();
+  challenge = BN_new();
+  aux = BN_new();
+
+  /* Generate a random challenge. */
+  BN_rand(challenge, 256, 0, 0);
+  BN_mod(challenge, challenge, n, ctx);
+  
+  /* Create the public key data structure. */
+  pk = RSA_new();
+  pk->e = BN_new();
+  BN_copy(pk->e, e);
+  pk->n = BN_new();
+  BN_copy(pk->n, n);
+
+  /* Encrypt the challenge with the public key. */
+  rsa_public_encrypt(encrypted_challenge, challenge, pk);
+  RSA_free(pk);
+
+  /* Send the encrypted challenge to the client. */
+  packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
+  packet_put_bignum(encrypted_challenge);
+  packet_send();
+  packet_write_wait();
+
+  /* The response is MD5 of decrypted challenge plus session id. */
+  len = BN_num_bytes(challenge);
+  assert(len <= 32 && len);
+  memset(buf, 0, 32);
+  BN_bn2bin(challenge, buf + 32 - len);
+  MD5_Init(&md);
+  MD5_Update(&md, buf, 32);
+  MD5_Update(&md, session_id, 16);
+  MD5_Final(mdbuf, &md);
+
+  /* We will no longer need these. */
+  BN_clear_free(encrypted_challenge);
+  BN_clear_free(challenge);
+  BN_clear_free(aux);
+  BN_CTX_free(ctx);
+  
+  /* Wait for a response. */
+  packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE);
+  packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE);
+  for (i = 0; i < 16; i++)
+    response[i] = packet_get_char();
+
+  /* Verify that the response is the original challenge. */
+  if (memcmp(response, mdbuf, 16) != 0)
+    {
+      /* Wrong answer. */
+      return 0;
+    }
+
+  /* Correct answer. */
+  return 1;
+}
+
+/* Performs the RSA authentication dialog with the client.  This returns
+   0 if the client could not be authenticated, and 1 if authentication was
+   successful.  This may exit if there is a serious protocol violation. */
+
+int
+auth_rsa(struct passwd *pw, BIGNUM *client_n, int strict_modes)
+{
+  char line[8192];
+  int authenticated;
+  unsigned int bits;
+  FILE *f;
+  unsigned long linenum = 0;
+  struct stat st;
+  BIGNUM *e, *n;
+
+  /* Temporarily use the user's uid. */
+  temporarily_use_uid(pw->pw_uid);
+
+  /* The authorized keys. */
+  snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir,
+    SSH_USER_PERMITTED_KEYS);
+  
+  /* Fail quietly if file does not exist */
+  if (stat(line, &st) < 0)
+    {
+      /* Restore the privileged uid. */
+      restore_uid();
+      return 0;
+    }
+
+  /* Open the file containing the authorized keys. */
+  f = fopen(line, "r");
+  if (!f)
+    {
+      /* Restore the privileged uid. */
+      restore_uid();
+      packet_send_debug("Could not open %.900s for reading.", line);
+      packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
+      return 0;
+    }
+
+  if (strict_modes) {
+    int fail=0;
+    char buf[1024];
+    /* Check open file in order to avoid open/stat races */
+    if (fstat(fileno(f), &st) < 0 ||
+        (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
+        (st.st_mode & 022) != 0) {
+      snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
+               "bad ownership or modes for '%s'.", pw->pw_name, line);
+      fail=1;
+    }else{
+      /* Check path to SSH_USER_PERMITTED_KEYS */
+      int i;
+      static const char *check[] = {
+            "", SSH_USER_DIR, NULL
+      };
+      for (i=0; check[i]; i++) {
+        snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]);
+        if (stat(line, &st) < 0 ||
+            (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
+            (st.st_mode & 022) != 0) {
+          snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
+                   "bad ownership or modes for '%s'.", pw->pw_name, line);
+          fail=1;
+          break;
+        }
+      }
+    }
+    if (fail) {
+      log(buf);
+      packet_send_debug(buf);
+      restore_uid();
+      return 0;
+    }
+  } 
+
+  /* Flag indicating whether authentication has succeeded. */
+  authenticated = 0;
+  
+  /* Initialize mp-int variables. */
+  e = BN_new();
+  n = BN_new();
+
+  /* Go though the accepted keys, looking for the current key.  If found,
+     perform a challenge-response dialog to verify that the user really has
+     the corresponding private key. */
+  while (fgets(line, sizeof(line), f))
+    {
+      char *cp;
+      char *options;
+
+      linenum++;
+
+      /* Skip leading whitespace. */
+      for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
+	;
+
+      /* Skip empty and comment lines. */
+      if (!*cp || *cp == '\n' || *cp == '#')
+	continue;
+
+      /* Check if there are options for this key, and if so, save their 
+	 starting address and skip the option part for now.  If there are no 
+	 options, set the starting address to NULL. */
+      if (*cp < '0' || *cp > '9')
+	{
+	  int quoted = 0;
+	  options = cp;
+	  for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++)
+	    {
+	      if (*cp == '\\' && cp[1] == '"')
+		cp++; /* Skip both */
+	      else
+		if (*cp == '"')
+		  quoted = !quoted;
+	    }
+	}
+      else
+	options = NULL;
+      
+      /* Parse the key from the line. */
+      if (!auth_rsa_read_key(&cp, &bits, e, n))
+	{
+	  debug("%.100s, line %lu: bad key syntax", 
+		SSH_USER_PERMITTED_KEYS, linenum);
+	  packet_send_debug("%.100s, line %lu: bad key syntax", 
+			    SSH_USER_PERMITTED_KEYS, linenum);
+	  continue;
+	}
+      /* cp now points to the comment part. */
+
+      /* Check if the we have found the desired key (identified by its
+	 modulus). */
+      if (BN_cmp(n, client_n) != 0)
+	continue; /* Wrong key. */
+
+      /* We have found the desired key. */
+
+      /* Perform the challenge-response dialog for this key. */
+      if (!auth_rsa_challenge_dialog(bits, e, n))
+	{
+	  /* Wrong response. */
+	  log("Wrong response to RSA authentication challenge.");
+	  packet_send_debug("Wrong response to RSA authentication challenge.");
+	  continue;
+	}
+
+      /* Correct response.  The client has been successfully authenticated.
+	 Note that we have not yet processed the options; this will be reset
+	 if the options cause the authentication to be rejected. */
+      authenticated = 1;
+
+      /* RSA part of authentication was accepted.  Now process the options. */
+      if (options)
+	{
+	  while (*options && *options != ' ' && *options != '\t')
+	    {
+	      cp = "no-port-forwarding";
+	      if (strncmp(options, cp, strlen(cp)) == 0)
+		{
+		  packet_send_debug("Port forwarding disabled.");
+		  no_port_forwarding_flag = 1;
+		  options += strlen(cp);
+		  goto next_option;
+		}
+	      cp = "no-agent-forwarding";
+	      if (strncmp(options, cp, strlen(cp)) == 0)
+		{
+		  packet_send_debug("Agent forwarding disabled.");
+		  no_agent_forwarding_flag = 1;
+		  options += strlen(cp);
+		  goto next_option;
+		}
+	      cp = "no-X11-forwarding";
+	      if (strncmp(options, cp, strlen(cp)) == 0)
+		{
+		  packet_send_debug("X11 forwarding disabled.");
+		  no_x11_forwarding_flag = 1;
+		  options += strlen(cp);
+		  goto next_option;
+		}
+	      cp = "no-pty";
+	      if (strncmp(options, cp, strlen(cp)) == 0)
+		{
+		  packet_send_debug("Pty allocation disabled.");
+		  no_pty_flag = 1;
+		  options += strlen(cp);
+		  goto next_option;
+		}
+	      cp = "command=\"";
+	      if (strncmp(options, cp, strlen(cp)) == 0)
+		{
+		  int i;
+		  options += strlen(cp);
+		  forced_command = xmalloc(strlen(options) + 1);
+		  i = 0;
+		  while (*options)
+		    {
+		      if (*options == '"')
+			break;
+		      if (*options == '\\' && options[1] == '"')
+			{
+			  options += 2;
+			  forced_command[i++] = '"';
+			  continue;
+			}
+		      forced_command[i++] = *options++;
+		    }
+		  if (!*options)
+		    {
+		      debug("%.100s, line %lu: missing end quote",
+			    SSH_USER_PERMITTED_KEYS, linenum);
+		      packet_send_debug("%.100s, line %lu: missing end quote",
+					SSH_USER_PERMITTED_KEYS, linenum);
+		      continue;
+		    }
+		  forced_command[i] = 0;
+		  packet_send_debug("Forced command: %.900s", forced_command);
+		  options++;
+		  goto next_option;
+		}
+	      cp = "environment=\"";
+	      if (strncmp(options, cp, strlen(cp)) == 0)
+		{
+		  int i;
+		  char *s;
+		  struct envstring *new_envstring;
+		  options += strlen(cp);
+		  s = xmalloc(strlen(options) + 1);
+		  i = 0;
+		  while (*options)
+		    {
+		      if (*options == '"')
+			break;
+		      if (*options == '\\' && options[1] == '"')
+			{
+			  options += 2;
+			  s[i++] = '"';
+			  continue;
+			}
+		      s[i++] = *options++;
+		    }
+		  if (!*options)
+		    {
+		      debug("%.100s, line %lu: missing end quote",
+			    SSH_USER_PERMITTED_KEYS, linenum);
+		      packet_send_debug("%.100s, line %lu: missing end quote",
+					SSH_USER_PERMITTED_KEYS, linenum);
+		      continue;
+		    }
+		  s[i] = 0;
+		  packet_send_debug("Adding to environment: %.900s", s);
+		  debug("Adding to environment: %.900s", s);
+		  options++;
+		  new_envstring = xmalloc(sizeof(struct envstring));
+		  new_envstring->s = s;
+		  new_envstring->next = custom_environment;
+		  custom_environment = new_envstring;
+		  goto next_option;
+		}
+	      cp = "from=\"";
+	      if (strncmp(options, cp, strlen(cp)) == 0)
+		{
+		  char *patterns = xmalloc(strlen(options) + 1);
+		  int i;
+		  options += strlen(cp);
+		  i = 0;
+		  while (*options)
+		    {
+		      if (*options == '"')
+			break;
+		      if (*options == '\\' && options[1] == '"')
+			{
+			  options += 2;
+			  patterns[i++] = '"';
+			  continue;
+			}
+		      patterns[i++] = *options++;
+		    }
+		  if (!*options)
+		    {
+		      debug("%.100s, line %lu: missing end quote",
+			    SSH_USER_PERMITTED_KEYS, linenum);
+		      packet_send_debug("%.100s, line %lu: missing end quote",
+					SSH_USER_PERMITTED_KEYS, linenum);
+		      continue;
+		    }
+		  patterns[i] = 0;
+		  options++;
+		  if (!match_hostname(get_canonical_hostname(), patterns,
+				     strlen(patterns)) &&
+		      !match_hostname(get_remote_ipaddr(), patterns,
+				      strlen(patterns)))
+		    {
+		      log("RSA authentication tried for %.100s with correct key but not from a permitted host (host=%.200s, ip=%.200s).",
+			  pw->pw_name, get_canonical_hostname(),
+			  get_remote_ipaddr());
+		      packet_send_debug("Your host '%.200s' is not permitted to use this key for login.",
+					get_canonical_hostname());
+		      xfree(patterns);
+		      authenticated = 0;
+		      break;
+		    }
+		  xfree(patterns);
+		  /* Host name matches. */
+		  goto next_option;
+		}
+	    bad_option:
+	      /* Unknown option. */
+	      log("Bad options in %.100s file, line %lu: %.50s",
+		  SSH_USER_PERMITTED_KEYS, linenum, options);
+	      packet_send_debug("Bad options in %.100s file, line %lu: %.50s",
+				SSH_USER_PERMITTED_KEYS, linenum, options);
+	      authenticated = 0;
+	      break;
+
+	    next_option:
+	      /* Skip the comma, and move to the next option (or break out
+		 if there are no more). */
+	      if (!*options)
+		fatal("Bugs in auth-rsa.c option processing.");
+	      if (*options == ' ' || *options == '\t')
+		break; /* End of options. */
+	      if (*options != ',')
+		goto bad_option;
+	      options++;
+	      /* Process the next option. */
+	      continue;
+	    }
+	}
+
+      /* Break out of the loop if authentication was successful; otherwise
+	 continue searching. */
+      if (authenticated)
+	break;
+    }
+
+  /* Restore the privileged uid. */
+  restore_uid();
+
+  /* Close the file. */
+  fclose(f);
+  
+  /* Clear any mp-int variables. */
+  BN_clear_free(n);
+  BN_clear_free(e);
+
+  if (authenticated)
+    packet_send_debug("RSA authentication accepted.");
+
+  /* Return authentication result. */
+  return authenticated;
+}