[binutils-gdb] DWARF reader: Reject sections with invalid sizes

[gdb-buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 950b74950f6020eda38647f22e9077ac7f68ca49 ***

commit 950b74950f6020eda38647f22e9077ac7f68ca49
Author:     Keith Seitz <keiths@redhat.com>
AuthorDate: Wed Oct 16 11:33:59 2019 -0700
Commit:     Keith Seitz <keiths@redhat.com>
CommitDate: Wed Oct 16 11:35:16 2019 -0700

    DWARF reader: Reject sections with invalid sizes
    
    This is another fuzzer bug, gdb/23567.  This time, the fuzzer has
    specifically altered the size of .debug_str:
    
    $ eu-readelf -S objdump
    Section Headers:
    [Nr] Name                 Type         Addr             Off      Size     ES Flags Lk Inf Al
    [31] .debug_str           PROGBITS     0000000000000000 0057116d ffffffffffffffff  1 MS     0   0  1
    
    When this file is loaded into GDB, the DWARF reader crashes attempting
    to access the string table (or it may just store a bunch of nonsense):
    
    [gdb-8.3-6-fc30]
    $ gdb -nx -q objdump
    BFD: warning: /path/to/objdump has a corrupt section with a size (ffffffffffffffff) larger than the file size
    Reading symbols from /path/to/objdump...
    Segmentation fault (core dumped)
    
    Nick has already committed a BFD patch to issue the warning seen above.
    
    [gdb master 6acc1a0b]
    $ gdb -BFD: warning: /path/to/objdump has a corrupt section with a size (ffffffffffffffff) larger than the file size
    Reading symbols from /path/to/objdump...
    (gdb) inf func
    All defined functions:
    
    File ./../include/dwarf2.def:
    186:    const
    
                  8 *>(.:
                         ;'@B);
    747:    const
    
                  8 *(.:
                         ;'@B);
    701:    const
    
                  8 *D 
                         (.:
                            ;'@B);
    71:     const
    
                  8 *(.:
                        ;'@B);
    /* and more gibberish  */
    
    Consider read_indirect_string_at_offset_from:
    
    static const char *
    read_indirect_string_at_offset_from (struct objfile *objfile,
                                         bfd *abfd, LONGEST str_offset,
                                         struct dwarf2_section_info *sect,
                                         const char *form_name,
                                         const char *sect_name)
    {
      dwarf2_read_section (objfile, sect);
      if (sect->buffer == NULL)
        error (_("%s used without %s section [in module %s]"),
               form_name, sect_name, bfd_get_filename (abfd));
      if (str_offset >= sect->size)
        error (_("%s pointing outside of %s section [in module %s]"),
               form_name, sect_name, bfd_get_filename (abfd));
      gdb_assert (HOST_CHAR_BIT == 8);
      if (sect->buffer[str_offset] == '\0')
        return NULL;
      return (const char *) (sect->buffer + str_offset);
    }
    
    With sect_size being ginormous, the code attempts to access
    sect->buffer[GINORMOUS], and depending on the layout of memory,
    GDB either stores a bunch of gibberish strings or crashes.
    
    This is an attempt to mitigate this by implementing a similar approach
    used by BFD. In our case, we simply reject the section with the invalid
    length:
    
    $ ./gdb -nx -q objdump
    BFD: warning: /path/to/objdump has a corrupt section with a size (ffffffffffffffff) larger than the file size
    Reading symbols from /path/to/objdump...
    
    warning: Discarding section .debug_str which has a section size (ffffffffffffffff) larger than the file size [in module /path/to/objdump]
    DW_FORM_strp used without .debug_str section [in module /path/to/objdump]
    (No debugging symbols found in /path/to/objdump)
    (gdb)
    
    Unfortunately, I have not found a way to regression test this, since it
    requires poking ELF section headers.
    
    gdb/ChangeLog:
    2019-10-16  Keith Seitz  <keiths@redhat.com>
    
            PR gdb/23567
            * dwarf2read.c (dwarf2_per_objfile::locate_sections): Discard
            sections whose size is greater than the file size.
    
    Change-Id: I896ac3b4eb2207c54e8e05c16beab3051d9b4b2f

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 6de9f3d01f..d11dbfbfcf 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,9 @@
+2019-10-16  Keith Seitz  <keiths@redhat.com>
+
+	PR gdb/23567
+	* dwarf2read.c (dwarf2_per_objfile::locate_sections): Discard
+	sections whose size is greater than the file size.
+
 2019-10-16  Jim Wilson  <jimw@sifive.com>
 
 	* riscv-tdep.c (riscv_gcc_target_options): New.
diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 0443b55d89..a78f818e0e 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -2338,6 +2338,15 @@ dwarf2_per_objfile::locate_sections (bfd *abfd, asection *sectp,
   if ((aflag & SEC_HAS_CONTENTS) == 0)
     {
     }
+  else if (elf_section_data (sectp)->this_hdr.sh_size
+	   > bfd_get_file_size (abfd))
+    {
+      bfd_size_type size = elf_section_data (sectp)->this_hdr.sh_size;
+      warning (_("Discarding section %s which has a section size (%s"
+		 ") larger than the file size [in module %s]"),
+	       bfd_section_name (sectp), phex_nz (size, sizeof (size)),
+	       bfd_get_filename (abfd));
+    }
   else if (section_is_p (sectp->name, &names.info))
     {
       this->info.s.section = sectp;