When writing ELF files in libelf, fill the gap between sections even if only

the section at the start of the gap has been changed.

1 files changed, 95 insertions, 44 deletions

diff --git a/libelf/elf32_updatefile.c b/libelf/elf32_updatefile.c
index f23035a5..def4c09a 100644
--- a/libelf/elf32_updatefile.c
+++ b/libelf/elf32_updatefile.c
@@ -126,11 +126,10 @@ int
 internal_function
 __elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
 {
-  ElfW2(LIBELFBITS,Ehdr) *ehdr;
-  char *last_position;
+  bool previous_scn_changed = false;
 
   /* We need the ELF header several times.  */
-  ehdr = elf->state.ELFW(elf,LIBELFBITS).ehdr;
+  ElfW2(LIBELFBITS,Ehdr) *ehdr = elf->state.ELFW(elf,LIBELFBITS).ehdr;
 
   /* Write out the ELF header.  */
   if ((elf->state.ELFW(elf,LIBELFBITS).ehdr_flags | elf->flags) & ELF_F_DIRTY)
@@ -160,6 +159,10 @@ __elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
 		sizeof (ElfW2(LIBELFBITS,Ehdr)));
 
       elf->state.ELFW(elf,LIBELFBITS).ehdr_flags &= ~ELF_F_DIRTY;
+
+      /* We start writing sections after the ELF header only if there is
+	 no program header.  */
+      previous_scn_changed = elf->state.ELFW(elf,LIBELFBITS).phdr == NULL;
     }
 
   /* Write out the program header table.  */
@@ -200,14 +203,19 @@ __elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
 		sizeof (ElfW2(LIBELFBITS,Phdr)) * ehdr->e_phnum);
 
       elf->state.ELFW(elf,LIBELFBITS).phdr_flags &= ~ELF_F_DIRTY;
+
+      /* We modified the program header.  Maybe this created a gap so
+	 we have to write fill bytes, if necessary.  */
+      previous_scn_changed = true;
     }
 
   /* From now on we have to keep track of the last position to eventually
      fill the gaps with the prescribed fill byte.  */
-  last_position = ((char *) elf->map_address + elf->start_offset
-		   + MAX (elf_typesize (LIBELFBITS, ELF_T_EHDR, 1),
-			  ehdr->e_phoff)
-		   + elf_typesize (LIBELFBITS, ELF_T_PHDR, ehdr->e_phnum));
+  char *last_position = ((char *) elf->map_address + elf->start_offset
+			 + MAX (elf_typesize (LIBELFBITS, ELF_T_EHDR, 1),
+				ehdr->e_phoff)
+			 + elf_typesize (LIBELFBITS, ELF_T_PHDR,
+					 ehdr->e_phnum));
 
   /* Write all the sections.  Well, only those which are modified.  */
   if (shnum > 0)
@@ -286,7 +294,7 @@ __elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
 	  if (scn->index == 0)
 	    {
 	      /* The dummy section header entry.  It should not be
-		 possible to make this "section" as dirty.  */
+		 possible to mark this "section" as dirty.  */
 	      assert ((scn->flags & ELF_F_DIRTY) == 0);
 	      continue;
 	    }
@@ -298,6 +306,25 @@ __elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
 	  char *scn_start = ((char *) elf->map_address
 			     + elf->start_offset + shdr->sh_offset);
 	  Elf_Data_List *dl = &scn->data_list;
+	  bool scn_changed = false;
+
+	  void fill_mmap (size_t offset)
+	  {
+	    size_t written = 0;
+
+	    if (last_position < shdr_start)
+	      {
+		written = MIN (scn_start + offset - last_position,
+			       shdr_start - last_position);
+
+		memset (last_position, __libelf_fill_byte, written);
+	      }
+
+	    if (last_position + written != scn_start + offset
+		&& shdr_end < scn_start + offset)
+	      memset (shdr_end, __libelf_fill_byte,
+		      scn_start + offset - shdr_end);
+	  }
 
 	  if (scn->data_list_rear != NULL)
 	    do
@@ -307,31 +334,15 @@ __elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
 		assert (dl->data.d.d_size <= (shdr->sh_size
 					      - (GElf_Off) dl->data.d.d_off));
 
+		/* If there is a gap, fill it.  */
+		if (scn_start + dl->data.d.d_off > last_position
+		    && ((previous_scn_changed && dl->data.d.d_off == 0)
+			|| ((scn->flags | dl->flags | elf->flags)
+			    & ELF_F_DIRTY) != 0))
+		  fill_mmap (dl->data.d.d_off);
+
 		if ((scn->flags | dl->flags | elf->flags) & ELF_F_DIRTY)
 		  {
-		    if (scn_start + dl->data.d.d_off > last_position)
-		      {
-			/* This code assumes that the data blocks for
-			   a section are ordered by offset.  */
-			size_t written = 0;
-
-			if (last_position < shdr_start)
-			  {
-			    written = MIN (scn_start + dl->data.d.d_off
-					   - last_position,
-					   shdr_start - last_position);
-
-			    memset (last_position, __libelf_fill_byte,
-				    written);
-			  }
-
-			if (last_position + written
-			    != scn_start + dl->data.d.d_off
-			    && shdr_end < scn_start + dl->data.d.d_off)
-			  memset (shdr_end, __libelf_fill_byte,
-				  scn_start + dl->data.d.d_off - shdr_end);
-		      }
-
 		    /* Let it go backward if the sections use a bogus
 		       layout with overlaps.  We'll overwrite the stupid
 		       user's section data with the latest one, rather than
@@ -359,6 +370,8 @@ __elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
 		      last_position = mempcpy (last_position,
 					       dl->data.d.d_buf,
 					       dl->data.d.d_size);
+
+		    scn_changed = true;
 		  }
 		else
 		  last_position += dl->data.d.d_size;
@@ -372,9 +385,18 @@ __elfw2(LIBELFBITS,updatemmap) (Elf *elf, int change_bo, size_t shnum)
 	      }
 	    while (dl != NULL);
 	  else
-	    /* We have to trust the existing section header information.  */
-	    last_position = scn_start + shdr->sh_size;
+	    {
+	      /* If the previous section (or the ELF/program
+		 header) changed we might have to fill the gap.  */
+	      if (scn_start > last_position && previous_scn_changed)
+		fill_mmap (0);
+
+	      /* We have to trust the existing section header information.  */
+	      last_position = scn_start + shdr->sh_size;
+	    }
 
+
+	  previous_scn_changed = scn_changed;
 	next:
 	  scn->flags &= ~ELF_F_DIRTY;
 	}
@@ -480,6 +502,7 @@ __elfw2(LIBELFBITS,updatefile) (Elf *elf, int change_bo, size_t shnum)
 {
   char fillbuf[FILLBUFSIZE];
   size_t filled = 0;
+  bool previous_scn_changed = false;
 
   /* We need the ELF header several times.  */
   ElfW2(LIBELFBITS,Ehdr) *ehdr = elf->state.ELFW(elf,LIBELFBITS).ehdr;
@@ -523,6 +546,10 @@ __elfw2(LIBELFBITS,updatefile) (Elf *elf, int change_bo, size_t shnum)
 	}
 
       elf->state.ELFW(elf,LIBELFBITS).ehdr_flags &= ~ELF_F_DIRTY;
+
+      /* We start writing sections after the ELF header only if there is
+	 no program header.  */
+      previous_scn_changed = elf->state.ELFW(elf,LIBELFBITS).phdr == NULL;
     }
 
   /* If the type sizes should be different at some time we have to
@@ -588,6 +615,10 @@ __elfw2(LIBELFBITS,updatefile) (Elf *elf, int change_bo, size_t shnum)
       free (tmp_phdr);
 
       elf->state.ELFW(elf,LIBELFBITS).phdr_flags &= ~ELF_F_DIRTY;
+
+      /* We modified the program header.  Maybe this created a gap so
+	 we have to write fill bytes, if necessary.  */
+      previous_scn_changed = true;
     }
 
   /* From now on we have to keep track of the last position to eventually
@@ -629,7 +660,7 @@ __elfw2(LIBELFBITS,updatefile) (Elf *elf, int change_bo, size_t shnum)
 	  if (scn->index == 0)
 	    {
 	      /* The dummy section header entry.  It should not be
-		 possible to make this "section" as dirty.  */
+		 possible to mark this "section" as dirty.  */
 	      assert ((scn->flags & ELF_F_DIRTY) == 0);
 	      continue;
 	    }
@@ -640,24 +671,29 @@ __elfw2(LIBELFBITS,updatefile) (Elf *elf, int change_bo, size_t shnum)
 
 	  off_t scn_start = elf->start_offset + shdr->sh_offset;
 	  Elf_Data_List *dl = &scn->data_list;
+	  bool scn_changed = false;
 
 	  if (scn->data_list_rear != NULL)
 	    do
 	      {
+		/* If there is a gap, fill it.  */
+		if (scn_start + dl->data.d.d_off > last_offset
+		    && ((previous_scn_changed && dl->data.d.d_off == 0)
+			|| ((scn->flags | dl->flags | elf->flags)
+			    & ELF_F_DIRTY) != 0))
+		  {
+		    if (unlikely (fill (elf->fildes, last_offset,
+					(scn_start + dl->data.d.d_off)
+					- last_offset, fillbuf,
+					&filled) != 0))
+		      return 1;
+		  }
+
 		if ((scn->flags | dl->flags | elf->flags) & ELF_F_DIRTY)
 		  {
 		    char tmpbuf[MAX_TMPBUF];
 		    void *buf = dl->data.d.d_buf;
 
-		    if (scn_start + dl->data.d.d_off > last_offset)
-		      {
-			if (unlikely (fill (elf->fildes, last_offset,
-					    (scn_start + dl->data.d.d_off)
-					    - last_offset, fillbuf,
-					    &filled) != 0))
-			  return 1;
-		      }
-
 		    /* Let it go backward if the sections use a bogus
 		       layout with overlaps.  We'll overwrite the stupid
 		       user's section data with the latest one, rather than
@@ -704,6 +740,8 @@ __elfw2(LIBELFBITS,updatefile) (Elf *elf, int change_bo, size_t shnum)
 
 		    if (buf != dl->data.d.d_buf && buf != tmpbuf)
 		      free (buf);
+
+		    scn_changed = true;
 		  }
 
 		last_offset += dl->data.d.d_size;
@@ -714,8 +752,21 @@ __elfw2(LIBELFBITS,updatefile) (Elf *elf, int change_bo, size_t shnum)
 	      }
 	    while (dl != NULL);
 	  else
-	    last_offset = scn_start + shdr->sh_size;
+	    {
+	      /* If the previous section (or the ELF/program
+		 header) changed we might have to fill the gap.  */
+	      if (scn_start > last_offset && previous_scn_changed)
+		{
+		  if (unlikely (fill (elf->fildes, last_offset,
+				      scn_start - last_offset, fillbuf,
+				      &filled) != 0))
+		    return 1;
+		}
+
+	      last_offset = scn_start + shdr->sh_size;
+	    }
 
+	  previous_scn_changed = scn_changed;
 	next:
 	  /* Collect the section header table information.  */
 	  if (unlikely (change_bo))