Created attachment 13550 [details]
I crashed `readelf -w` with a fuzzer. The original error message was "readelf: dwarf.c:2336: void display_discr_list(unsigned long, dwarf_vma, unsigned char *, const unsigned char *, int): Assertion `uvalue > 0' failed."
- Compiler: clang12
- Platform: Ubuntu 18.04.5 LTS, x86_64
- Reproduce: run `readelf -w poc`
The master branch has been updated by Alan Modra <email@example.com>:
Author: Alan Modra <firstname.lastname@example.org>
Date: Sat Jul 10 09:34:30 2021 +0930
PR28069, assertion fail in dwarf.c:display_discr_list
We shouldn't be asserting on anything to do with leb128 values, or
reporting file and line numbers when something unexpected happens.
leb128 data is of indeterminate length, perfect for fuzzer mayhem.
It would only make sense to assert or report dwarf.c/readelf.c source
lines if the code had already sized and sanity checked the leb128
After removing the assertions, the testcase then gave:
<37> DW_AT_discr_list : 5 byte block: 0 0 0 0 0 (label 0, label 0, label 0, label 0, <corrupt>
readelf: Warning: corrupt discr_list - unrecognized discriminant byte 0x5
<3d> DW_AT_encoding : 0 (void)
<3e> DW_AT_identifier_case: 0 (case_sensitive)
<3f> DW_AT_virtuality : 0 (none)
<40> DW_AT_decimal_sign: 5 (trailing separate)
So the DW_AT_discr_list was showing more data than just the 5 byte
block. That happened due to "end" pointing a long way past the end of
block, and uvalue decrementing past zero on one of the leb128 bytes.
* dwarf.c (display_discr_list): Remove assertions. Delete "end"
parameter, use initial "data" pointer as the end. Formatting.
Don't count down bytes as they are read.
(read_and_display_attr_value): Adjust display_discr_list call.
(read_and_print_leb128): Don't pass __FILE__ and __LINE__ to
* dwarf.h (report_leb_status): Don't report file and line
numbers. Delete file and lnum parameters,
(READ_ULEB, READ_SLEB): Adjust.
Fixed mainline, won't backport to 2.37 since this bug is only tickled by fuzzed objects.