libelf/elf_strptr.c

/* Return string pointer from string section.
   Copyright (C) 1998-2002, 2004, 2008, 2009, 2015 Red Hat, Inc.
   This file is part of elfutils.
   Contributed by Ulrich Drepper <drepper@redhat.com>, 1998.

   This file is free software; you can redistribute it and/or modify
   it under the terms of either

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at
       your option) any later version

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at
       your option) any later version

   or both in parallel, as here.

   elfutils is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   General Public License for more details.

   You should have received copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see <http://www.gnu.org/licenses/>.  */

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <libelf.h>
#include <stdbool.h>
#include <stddef.h>

#include "libelfP.h"


static void *
get_zdata (Elf_Scn *strscn)
{
  size_t zsize, zalign;
  void *zdata = __libelf_decompress_elf (strscn, &zsize, &zalign);
  if (zdata == NULL)
    return NULL;

  strscn->zdata_base = zdata;
  strscn->zdata_size = zsize;
  strscn->zdata_align = zalign;

  return zdata;
}

static bool validate_str (const char *str, size_t from, size_t to)
{
#if HAVE_DECL_MEMRCHR
  return memrchr (&str[from], '\0', to - from) != NULL;
#else
  do {
    if (to <= from)
      return false;

    to--;
  } while (str[to]);

  return true;
#endif
}

char *
elf_strptr (Elf *elf, size_t idx, size_t offset)
{
  if (elf == NULL)
    return NULL;

  if (elf->kind != ELF_K_ELF)
    {
      __libelf_seterrno (ELF_E_INVALID_HANDLE);
      return NULL;
    }

  rwlock_rdlock (elf->lock);

  char *result = NULL;
  Elf_Scn *strscn;

  /* Find the section in the list.  */
  Elf_ScnList *runp = (elf->class == ELFCLASS32
		       || (offsetof (struct Elf, state.elf32.scns)
			   == offsetof (struct Elf, state.elf64.scns))
		       ? &elf->state.elf32.scns : &elf->state.elf64.scns);
  while (1)
    {
      if (idx < runp->max)
	{
	  if (idx < runp->cnt)
	    strscn = &runp->data[idx];
	  else
	    {
	      __libelf_seterrno (ELF_E_INVALID_INDEX);
	      goto out;
	    }
	  break;
	}

      idx -= runp->max;

      runp = runp->next;
      if (runp == NULL)
	{
	  __libelf_seterrno (ELF_E_INVALID_INDEX);
	  goto out;
	}
    }

  size_t sh_size = 0;
  if (elf->class == ELFCLASS32)
    {
      Elf32_Shdr *shdr = strscn->shdr.e32 ?: __elf32_getshdr_rdlock (strscn);
      if (unlikely (shdr->sh_type != SHT_STRTAB))
	{
	  /* This is no string section.  */
	  __libelf_seterrno (ELF_E_INVALID_SECTION);
	  goto out;
	}

      if ((shdr->sh_flags & SHF_COMPRESSED) == 0)
	sh_size = shdr->sh_size;
      else
	{
	  if (strscn->zdata_base == NULL && get_zdata (strscn) == NULL)
	    goto out;
	  sh_size = strscn->zdata_size;
	}

      if (unlikely (offset >= sh_size))
	{
	  /* The given offset is too big, it is beyond this section.  */
	  __libelf_seterrno (ELF_E_OFFSET_RANGE);
	  goto out;
	}
    }
  else
    {
      Elf64_Shdr *shdr = strscn->shdr.e64 ?: __elf64_getshdr_rdlock (strscn);
      if (unlikely (shdr->sh_type != SHT_STRTAB))
	{
	  /* This is no string section.  */
	  __libelf_seterrno (ELF_E_INVALID_SECTION);
	  goto out;
	}

      if ((shdr->sh_flags & SHF_COMPRESSED) == 0)
	sh_size = shdr->sh_size;
      else
	{
	  if (strscn->zdata_base == NULL && get_zdata (strscn) == NULL)
	    goto out;
	  sh_size = strscn->zdata_size;
	}

      if (unlikely (offset >= sh_size))
	{
	  /* The given offset is too big, it is beyond this section.  */
	  __libelf_seterrno (ELF_E_OFFSET_RANGE);
	  goto out;
	}
    }

  if (strscn->rawdata_base == NULL && ! strscn->data_read)
    {
      rwlock_unlock (elf->lock);
      rwlock_wrlock (elf->lock);
      if (strscn->rawdata_base == NULL && ! strscn->data_read
	/* Read the section data.  */
	  && __libelf_set_rawdata_wrlock (strscn) != 0)
	goto out;
    }

  if (unlikely (strscn->zdata_base != NULL))
    {
      /* Make sure the string is NUL terminated.  Start from the end,
         which very likely is a NUL char.  */
      if (likely (validate_str (strscn->zdata_base, offset, sh_size)))
        result = &strscn->zdata_base[offset];
      else
        __libelf_seterrno (ELF_E_INVALID_INDEX);
    }
  else if (likely (strscn->data_list_rear == NULL))
    {
      // XXX The above is currently correct since elf_newdata will
      // make sure to convert the rawdata into the datalist if
      // necessary. But it would be more efficient to keep the rawdata
      // unconverted and only then iterate over the rest of the (newly
      // added data) list.  Note that when the ELF file is mmapped
      // rawdata_base can be set while rawdata.d hasn't been
      // initialized yet (when data_read is zero). So we cannot just
      // look at the rawdata.d.d_size.

      /* Make sure the string is NUL terminated.  Start from the end,
	 which very likely is a NUL char.  */
      if (likely (validate_str (strscn->rawdata_base, offset, sh_size)))
	result = &strscn->rawdata_base[offset];
      else
	__libelf_seterrno (ELF_E_INVALID_INDEX);
    }
  else
    {
      /* This is a file which is currently created.  Use the list of
	 data blocks.  */
      struct Elf_Data_List *dl = &strscn->data_list;
      while (dl != NULL)
	{
	  if (offset >= (size_t) dl->data.d.d_off
	      && offset < dl->data.d.d_off + dl->data.d.d_size)
	    {
	      /* Make sure the string is NUL terminated.  Start from
		 the end, which very likely is a NUL char.  */
	      if (likely (validate_str ((char *) dl->data.d.d_buf,
					offset - dl->data.d.d_off,
					dl->data.d.d_size)))
		result = ((char *) dl->data.d.d_buf
			  + (offset - dl->data.d.d_off));
	      else
		__libelf_seterrno (ELF_E_INVALID_INDEX);
	      break;
	    }

	  dl = dl->next;
	}
    }

 out:
  rwlock_unlock (elf->lock);

  return result;
}
INTDEF(elf_strptr)