grp/grp-merge.c

   1 /* Group merging implementation.
   2    Copyright (C) 2016-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <stdlib.h>
  21 #include <string.h>
  22 #include <grp.h>
  23 #include <grp-merge.h>
  24
  25 #define BUFCHECK(size)                  \
  26   ({                                    \
  27     do                                  \
  28       {                                 \
  29         if (c + (size) > buflen)        \
  30           {                             \
  31             free (members);             \
  32             return ERANGE;              \
  33           }                             \
  34       }                                 \
  35     while (0);                          \
  36   })
  37
  38 int
  39 internal_function
  40 __copy_grp (const struct group srcgrp, const size_t buflen,
  41             struct group *destgrp, char *destbuf, char **endptr)
  42 {
  43   size_t i;
  44   size_t c = 0;
  45   size_t len;
  46   size_t memcount;
  47   char **members = NULL;
  48
  49   /* Copy the GID.  */
  50   destgrp->gr_gid = srcgrp.gr_gid;
  51
  52   /* Copy the name.  */
  53   len = strlen (srcgrp.gr_name) + 1;
  54   BUFCHECK (len);
  55   memcpy (&destbuf[c], srcgrp.gr_name, len);
  56   destgrp->gr_name = &destbuf[c];
  57   c += len;
  58
  59   /* Copy the password.  */
  60   len = strlen (srcgrp.gr_passwd) + 1;
  61   BUFCHECK (len);
  62   memcpy (&destbuf[c], srcgrp.gr_passwd, len);
  63   destgrp->gr_passwd = &destbuf[c];
  64   c += len;
  65
  66   /* Count all of the members.  */
  67   for (memcount = 0; srcgrp.gr_mem[memcount]; memcount++)
  68     ;
  69
  70   /* Allocate a temporary holding area for the pointers to the member
  71      contents, including space for a NULL-terminator.  */
  72   members = malloc (sizeof (char *) * (memcount + 1));
  73   if (members == NULL)
  74     return ENOMEM;
  75
  76   /* Copy all of the group members to destbuf and add a pointer to each of
  77      them into the 'members' array.  */
  78   for (i = 0; srcgrp.gr_mem[i]; i++)
  79     {
  80       len = strlen (srcgrp.gr_mem[i]) + 1;
  81       BUFCHECK (len);
  82       memcpy (&destbuf[c], srcgrp.gr_mem[i], len);
  83       members[i] = &destbuf[c];
  84       c += len;
  85     }
  86   members[i] = NULL;
  87
  88   /* Copy the pointers from the members array into the buffer and assign them
  89      to the gr_mem member of destgrp.  */
  90   destgrp->gr_mem = (char **) &destbuf[c];
  91   len = sizeof (char *) * (memcount + 1);
  92   BUFCHECK (len);
  93   memcpy (&destbuf[c], members, len);
  94   c += len;
  95   free (members);
  96   members = NULL;
  97
  98   /* Save the count of members at the end.  */
  99   BUFCHECK (sizeof (size_t));
 100   memcpy (&destbuf[c], &memcount, sizeof (size_t));
 101   c += sizeof (size_t);
 102
 103   if (endptr)
 104     *endptr = destbuf + c;
 105   return 0;
 106 }
 107 libc_hidden_def (__copy_grp)
 108
 109 /* Check that the name, GID and passwd fields match, then
 110    copy in the gr_mem array.  */
 111 int
 112 internal_function
 113 __merge_grp (struct group *savedgrp, char *savedbuf, char *savedend,
 114              size_t buflen, struct group *mergegrp, char *mergebuf)
 115 {
 116   size_t c, i, len;
 117   size_t savedmemcount;
 118   size_t memcount;
 119   size_t membersize;
 120   char **members = NULL;
 121
 122   /* We only support merging members of groups with identical names and
 123      GID values. If we hit this case, we need to overwrite the current
 124      buffer with the saved one (which is functionally equivalent to
 125      treating the new lookup as NSS_STATUS_NOTFOUND).  */
 126   if (mergegrp->gr_gid != savedgrp->gr_gid
 127       || strcmp (mergegrp->gr_name, savedgrp->gr_name))
 128     return __copy_grp (*savedgrp, buflen, mergegrp, mergebuf, NULL);
 129
 130   /* Get the count of group members from the last sizeof (size_t) bytes in the
 131      mergegrp buffer.  */
 132   savedmemcount = (size_t) *(savedend - sizeof (size_t));
 133
 134   /* Get the count of new members to add.  */
 135   for (memcount = 0; mergegrp->gr_mem[memcount]; memcount++)
 136     ;
 137
 138   /* Create a temporary array to hold the pointers to the member values from
 139      both the saved and merge groups.  */
 140   membersize = savedmemcount + memcount + 1;
 141   members = malloc (sizeof (char *) * membersize);
 142   if (members == NULL)
 143     return ENOMEM;
 144
 145   /* Copy in the existing member pointers from the saved group
 146      Note: this is not NULL-terminated yet.  */
 147   memcpy (members, savedgrp->gr_mem, sizeof (char *) * savedmemcount);
 148
 149   /* Back up into the savedbuf until we get back to the NULL-terminator of the
 150      group member list. (This means walking back savedmemcount + 1 (char *) pointers
 151      and the member count value.
 152      The value of c is going to be the used length of the buffer backed up by
 153      the member count and further backed up by the size of the pointers.  */
 154   c = savedend - savedbuf
 155       - sizeof (size_t)
 156       - sizeof (char *) * (savedmemcount + 1);
 157
 158   /* Add all the new group members, overwriting the old NULL-terminator while
 159      adding the new pointers to the temporary array.  */
 160   for (i = 0; mergegrp->gr_mem[i]; i++)
 161     {
 162       len = strlen (mergegrp->gr_mem[i]) + 1;
 163       BUFCHECK (len);
 164       memcpy (&savedbuf[c], mergegrp->gr_mem[i], len);
 165       members[savedmemcount + i] = &savedbuf[c];
 166       c += len;
 167     }
 168   /* Add the NULL-terminator.  */
 169   members[savedmemcount + memcount] = NULL;
 170
 171   /* Copy the member array back into the buffer after the member list and free
 172      the member array.  */
 173   savedgrp->gr_mem = (char **) &savedbuf[c];
 174   len = sizeof (char *) * membersize;
 175   BUFCHECK (len);
 176   memcpy (&savedbuf[c], members, len);
 177   c += len;
 178
 179   free (members);
 180   members = NULL;
 181
 182   /* Finally, copy the results back into mergebuf, since that's the buffer
 183      that we were provided by the caller.  */
 184   return __copy_grp (*savedgrp, buflen, mergegrp, mergebuf, NULL);
 185 }
 186 libc_hidden_def (__merge_grp)