grp/grp-merge.c

   1 /* Group merging implementation.
   2    Copyright (C) 2016-2021 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    <https://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 __copy_grp (const struct group srcgrp, const size_t buflen,
  40             struct group *destgrp, char *destbuf, char **endptr)
  41 {
  42   size_t i;
  43   size_t c = 0;
  44   size_t len;
  45   size_t memcount;
  46   char **members = NULL;
  47
  48   /* Copy the GID.  */
  49   destgrp->gr_gid = srcgrp.gr_gid;
  50
  51   /* Copy the name.  */
  52   len = strlen (srcgrp.gr_name) + 1;
  53   BUFCHECK (len);
  54   memcpy (&destbuf[c], srcgrp.gr_name, len);
  55   destgrp->gr_name = &destbuf[c];
  56   c += len;
  57
  58   /* Copy the password.  */
  59   len = strlen (srcgrp.gr_passwd) + 1;
  60   BUFCHECK (len);
  61   memcpy (&destbuf[c], srcgrp.gr_passwd, len);
  62   destgrp->gr_passwd = &destbuf[c];
  63   c += len;
  64
  65   /* Count all of the members.  */
  66   for (memcount = 0; srcgrp.gr_mem[memcount]; memcount++)
  67     ;
  68
  69   /* Allocate a temporary holding area for the pointers to the member
  70      contents, including space for a NULL-terminator.  */
  71   members = malloc (sizeof (char *) * (memcount + 1));
  72   if (members == NULL)
  73     return ENOMEM;
  74
  75   /* Copy all of the group members to destbuf and add a pointer to each of
  76      them into the 'members' array.  */
  77   for (i = 0; srcgrp.gr_mem[i]; i++)
  78     {
  79       len = strlen (srcgrp.gr_mem[i]) + 1;
  80       BUFCHECK (len);
  81       memcpy (&destbuf[c], srcgrp.gr_mem[i], len);
  82       members[i] = &destbuf[c];
  83       c += len;
  84     }
  85   members[i] = NULL;
  86
  87   /* Align for pointers.  We can't simply align C because we need to
  88      align destbuf[c].  */
  89   if ((((uintptr_t)destbuf + c) & (__alignof__(char **) - 1)) != 0)
  90     {
  91       uintptr_t mis_align = ((uintptr_t)destbuf + c) & (__alignof__(char **) - 1);
  92       c += __alignof__(char **) - mis_align;
  93     }
  94
  95   /* Copy the pointers from the members array into the buffer and assign them
  96      to the gr_mem member of destgrp.  */
  97   destgrp->gr_mem = (char **) &destbuf[c];
  98   len = sizeof (char *) * (memcount + 1);
  99   BUFCHECK (len);
 100   memcpy (&destbuf[c], members, len);
 101   c += len;
 102   free (members);
 103   members = NULL;
 104
 105   /* Save the count of members at the end.  */
 106   BUFCHECK (sizeof (size_t));
 107   memcpy (&destbuf[c], &memcount, sizeof (size_t));
 108   c += sizeof (size_t);
 109
 110   if (endptr)
 111     *endptr = destbuf + c;
 112   return 0;
 113 }
 114 libc_hidden_def (__copy_grp)
 115
 116 /* Check that the name, GID and passwd fields match, then
 117    copy in the gr_mem array.  */
 118 int
 119 __merge_grp (struct group *savedgrp, char *savedbuf, char *savedend,
 120              size_t buflen, struct group *mergegrp, char *mergebuf)
 121 {
 122   size_t c, i, len;
 123   size_t savedmemcount;
 124   size_t memcount;
 125   size_t membersize;
 126   char **members = NULL;
 127
 128   /* We only support merging members of groups with identical names and
 129      GID values. If we hit this case, we need to overwrite the current
 130      buffer with the saved one (which is functionally equivalent to
 131      treating the new lookup as NSS_STATUS_NOTFOUND).  */
 132   if (mergegrp->gr_gid != savedgrp->gr_gid
 133       || strcmp (mergegrp->gr_name, savedgrp->gr_name))
 134     return __copy_grp (*savedgrp, buflen, mergegrp, mergebuf, NULL);
 135
 136   /* Get the count of group members from the last sizeof (size_t) bytes in the
 137      mergegrp buffer.  */
 138   savedmemcount = *(size_t *) (savedend - sizeof (size_t));
 139
 140   /* Get the count of new members to add.  */
 141   for (memcount = 0; mergegrp->gr_mem[memcount]; memcount++)
 142     ;
 143
 144   /* Create a temporary array to hold the pointers to the member values from
 145      both the saved and merge groups.  */
 146   membersize = savedmemcount + memcount + 1;
 147   members = malloc (sizeof (char *) * membersize);
 148   if (members == NULL)
 149     return ENOMEM;
 150
 151   /* Copy in the existing member pointers from the saved group
 152      Note: this is not NULL-terminated yet.  */
 153   memcpy (members, savedgrp->gr_mem, sizeof (char *) * savedmemcount);
 154
 155   /* Back up into the savedbuf until we get back to the NULL-terminator of the
 156      group member list. (This means walking back savedmemcount + 1 (char *) pointers
 157      and the member count value.
 158      The value of c is going to be the used length of the buffer backed up by
 159      the member count and further backed up by the size of the pointers.  */
 160   c = savedend - savedbuf
 161       - sizeof (size_t)
 162       - sizeof (char *) * (savedmemcount + 1);
 163
 164   /* Add all the new group members, overwriting the old NULL-terminator while
 165      adding the new pointers to the temporary array.  */
 166   for (i = 0; mergegrp->gr_mem[i]; i++)
 167     {
 168       len = strlen (mergegrp->gr_mem[i]) + 1;
 169       BUFCHECK (len);
 170       memcpy (&savedbuf[c], mergegrp->gr_mem[i], len);
 171       members[savedmemcount + i] = &savedbuf[c];
 172       c += len;
 173     }
 174   /* Add the NULL-terminator.  */
 175   members[savedmemcount + memcount] = NULL;
 176
 177   /* Align for pointers.  We can't simply align C because we need to
 178      align savedbuf[c].  */
 179   if ((((uintptr_t)savedbuf + c) & (__alignof__(char **) - 1)) != 0)
 180     {
 181       uintptr_t mis_align = ((uintptr_t)savedbuf + c) & (__alignof__(char **) - 1);
 182       c += __alignof__(char **) - mis_align;
 183     }
 184
 185   /* Copy the member array back into the buffer after the member list and free
 186      the member array.  */
 187   savedgrp->gr_mem = (char **) &savedbuf[c];
 188   len = sizeof (char *) * membersize;
 189   BUFCHECK (len);
 190   memcpy (&savedbuf[c], members, len);
 191   c += len;
 192
 193   free (members);
 194   members = NULL;
 195
 196   /* Finally, copy the results back into mergebuf, since that's the buffer
 197      that we were provided by the caller.  */
 198   return __copy_grp (*savedgrp, buflen, mergegrp, mergebuf, NULL);
 199 }
 200 libc_hidden_def (__merge_grp)