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950b74950f
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
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