1  /* Get directory entries.  Linux non-LFS version.
       2     Copyright (C) 1993-2023 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 <dirent.h>
      20  
      21  #if !_DIRENT_MATCHES_DIRENT64
      22  
      23  # include <unistd.h>
      24  # include <string.h>
      25  # include <errno.h>
      26  
      27  # ifndef DIRENT_SET_DP_INO
      28  #  define DIRENT_SET_DP_INO(dp, value) (dp)->d_ino = (value)
      29  # endif
      30  
      31  /* Pack the dirent64 struct down into 32-bit offset/inode fields, and
      32     ensure that no overflow occurs.  */
      33  ssize_t
      34  __getdents (int fd, void *buf0, size_t nbytes)
      35  {
      36    char *buf = buf0;
      37  
      38    union
      39    {
      40      /* For !_DIRENT_MATCHES_DIRENT64 kernel 'linux_dirent64' has the same
      41         layout of 'struct dirent64'.  */
      42      struct dirent64 k;
      43      struct dirent u;
      44      char b[1];
      45    } *kbuf = (void *) buf, *outp, *inp;
      46    size_t kbytes = nbytes;
      47    off64_t last_offset = -1;
      48    ssize_t retval;
      49  
      50  # define size_diff (offsetof (struct dirent64, d_name) \
      51  		    - offsetof (struct dirent, d_name))
      52    char kbuftmp[sizeof (struct dirent) + size_diff];
      53    if (nbytes <= sizeof (struct dirent))
      54      kbuf = (void*) kbuftmp;
      55  
      56    retval = INLINE_SYSCALL_CALL (getdents64, fd, kbuf, kbytes);
      57    if (retval == -1)
      58      return -1;
      59  
      60    /* These two pointers might alias the same memory buffer.
      61       Standard C requires that we always use the same type for them,
      62       so we must use the union type.  */
      63    inp = kbuf;
      64    outp = (void *) buf;
      65  
      66    while (&inp->b < &kbuf->b + retval)
      67      {
      68        const size_t alignment = _Alignof (struct dirent);
      69        /* Since inp->k.d_reclen is already aligned for the kernel
      70           structure this may compute a value that is bigger
      71           than necessary.  */
      72        size_t old_reclen = inp->k.d_reclen;
      73        size_t new_reclen = ((old_reclen - size_diff + alignment - 1)
      74                             & ~(alignment - 1));
      75  
      76        /* Copy the data out of the old structure into temporary space.
      77           Then copy the name, which may overlap if BUF == KBUF.  */
      78        const uint64_t d_ino = inp->k.d_ino;
      79        const int64_t d_off = inp->k.d_off;
      80        const uint8_t d_type = inp->k.d_type;
      81  
      82        memmove (outp->u.d_name, inp->k.d_name,
      83                 old_reclen - offsetof (struct dirent64, d_name));
      84  
      85        /* Now we have copied the data from INP and access only OUTP.  */
      86  
      87        DIRENT_SET_DP_INO (&outp->u, d_ino);
      88        outp->u.d_off = d_off;
      89        if ((sizeof (outp->u.d_ino) != sizeof (inp->k.d_ino)
      90             && outp->u.d_ino != d_ino)
      91            || (sizeof (outp->u.d_off) != sizeof (inp->k.d_off)
      92                && outp->u.d_off != d_off))
      93          {
      94            /* Overflow.  If there was at least one entry before this one,
      95               return them without error, otherwise signal overflow.  */
      96            if (last_offset != -1)
      97              {
      98                __lseek64 (fd, last_offset, SEEK_SET);
      99                return outp->b - buf;
     100              }
     101  	  return INLINE_SYSCALL_ERROR_RETURN_VALUE (EOVERFLOW);
     102          }
     103  
     104        last_offset = d_off;
     105        outp->u.d_reclen = new_reclen;
     106        outp->u.d_type = d_type;
     107  
     108        inp = (void *) inp + old_reclen;
     109        outp = (void *) outp + new_reclen;
     110      }
     111  
     112    return outp->b - buf;
     113  }
     114  
     115  # undef DIRENT_SET_DP_INO
     116  
     117  #endif /* _DIRENT_MATCHES_DIRENT64  */