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From FEDORA_PATCHES Mon Sep 17 00:00:00 2001
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From: Keith Seitz <keiths@redhat.com>
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Date: Thu, 17 Oct 2019 09:44:15 -0700
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Subject: gdb-rhbz1742099-reject-sections-with-invalid-sizes.patch
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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;; Prevent buffer overflow with sections with invalid sizes.
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;; Keith Seitz, RH BZ 1740299.
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DWARF reader: Reject sections with invalid sizes
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This is another fuzzer bug, gdb/23567. This time, the fuzzer has
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specifically altered the size of .debug_str:
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$ eu-readelf -S objdump
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Section Headers:
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[Nr] Name Type Addr Off Size ES Flags Lk Inf Al
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[31] .debug_str PROGBITS 0000000000000000 0057116d ffffffffffffffff 1 MS 0 0 1
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When this file is loaded into GDB, the DWARF reader crashes attempting
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to access the string table (or it may just store a bunch of nonsense):
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[gdb-8.3-6-fc30]
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$ gdb -nx -q objdump
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BFD: warning: /path/to/objdump has a corrupt section with a size (ffffffffffffffff) larger than the file size
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Reading symbols from /path/to/objdump...
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Segmentation fault (core dumped)
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Nick has already committed a BFD patch to issue the warning seen above.
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[gdb master 6acc1a0b]
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$ gdb -BFD: warning: /path/to/objdump has a corrupt section with a size (ffffffffffffffff) larger than the file size
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Reading symbols from /path/to/objdump...
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(gdb) inf func
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All defined functions:
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File ./../include/dwarf2.def:
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186: const
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8 *>(.:
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;'@<40>B);
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747: const
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8 *<2A>(.:
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;'@<40>B);
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701: const
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8 *<2A>D <20>
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(.:
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;'@<40>B);
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71: const
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8 *(.:
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;'@<40>B);
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/* and more gibberish */
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Consider read_indirect_string_at_offset_from:
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static const char *
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read_indirect_string_at_offset_from (struct objfile *objfile,
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bfd *abfd, LONGEST str_offset,
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struct dwarf2_section_info *sect,
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const char *form_name,
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const char *sect_name)
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{
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dwarf2_read_section (objfile, sect);
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if (sect->buffer == NULL)
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error (_("%s used without %s section [in module %s]"),
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form_name, sect_name, bfd_get_filename (abfd));
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if (str_offset >= sect->size)
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error (_("%s pointing outside of %s section [in module %s]"),
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form_name, sect_name, bfd_get_filename (abfd));
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gdb_assert (HOST_CHAR_BIT == 8);
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if (sect->buffer[str_offset] == '\0')
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return NULL;
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return (const char *) (sect->buffer + str_offset);
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}
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With sect_size being ginormous, the code attempts to access
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sect->buffer[GINORMOUS], and depending on the layout of memory,
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GDB either stores a bunch of gibberish strings or crashes.
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This is an attempt to mitigate this by implementing a similar approach
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used by BFD. In our case, we simply reject the section with the invalid
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length:
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$ ./gdb -nx -q objdump
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BFD: warning: /path/to/objdump has a corrupt section with a size (ffffffffffffffff) larger than the file size
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Reading symbols from /path/to/objdump...
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warning: Discarding section .debug_str which has a section size (ffffffffffffffff) larger than the file size [in module /path/to/objdump]
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DW_FORM_strp used without .debug_str section [in module /path/to/objdump]
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(No debugging symbols found in /path/to/objdump)
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(gdb)
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Unfortunately, I have not found a way to regression test this, since it
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requires poking ELF section headers.
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gdb/ChangeLog:
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2019-10-16 Keith Seitz <keiths@redhat.com>
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PR gdb/23567
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* dwarf2read.c (dwarf2_per_objfile::locate_sections): Discard
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sections whose size is greater than the file size.
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Change-Id: I896ac3b4eb2207c54e8e05c16beab3051d9b4b2f
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diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
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--- a/gdb/dwarf2read.c
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+++ b/gdb/dwarf2read.c
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@@ -2335,6 +2335,15 @@ dwarf2_per_objfile::locate_sections (bfd *abfd, asection *sectp,
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if ((aflag & SEC_HAS_CONTENTS) == 0)
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{
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}
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+ else if (elf_section_data (sectp)->this_hdr.sh_size
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+ > bfd_get_file_size (abfd))
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+ {
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+ bfd_size_type size = elf_section_data (sectp)->this_hdr.sh_size;
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+ warning (_("Discarding section %s which has a section size (%s"
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+ ") larger than the file size [in module %s]"),
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+ bfd_section_name (abfd, sectp), phex_nz (size, sizeof (size)),
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+ bfd_get_filename (abfd));
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+ }
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else if (section_is_p (sectp->name, &names.info))
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{
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this->info.s.section = sectp;
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