I found some floating point exception in function arlib_add_symbols() in arlib.c of the latest elfutils-0.174 code base. I have confirmed them with GDB and Address Sanitizer.
Here are the POC files. Please use " ./eu-ranlib $POC " to reproduce this bug. I'll also show you the debugging process. It seems that this is caused by the divide-by-zero.
In arlib.c:255, there exist a division calculation:
> int nsyms = shdr->sh_size / shdr->sh_entsize;
I can provide you some testcases to make shdr->sh_entsize = 0. And you can use the testcases to reproduce the bug. Divide by zero is bad. We need to make a check before doing division calculation.
Created attachment 11336 [details]
I have also confirmed them with Address Sanitizer.
The ASAN dumps the stack trace as follows:
==2496==ERROR: AddressSanitizer: FPE on unknown address 0x0000004065d8 (pc 0x0000004065d8 bp 0x7ffd4c109620 sp 0x7ffd4c109550 T0)
#0 0x4065d7 in arlib_add_symbols /media/hjwang/01D3344861A8D2E0/wcventure/Project/elfutils/src/arlib.c:255
#1 0x4029c5 in handle_file /media/hjwang/01D3344861A8D2E0/wcventure/Project/elfutils/src/ranlib.c:193
#2 0x4029c5 in main /media/hjwang/01D3344861A8D2E0/wcventure/Project/elfutils/src/ranlib.c:110
#3 0x7fc97b51982f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
#4 0x403d28 in _start (/media/hjwang/01D3344861A8D2E0/wcventure/Project/elfutils/build/bin/eu-ranlib+0x403d28)
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: FPE /media/hjwang/01D3344861A8D2E0/wcventure/Project/elfutils/src/arlib.c:255 in arlib_add_symbols
Created attachment 11337 [details]
Please use " ./eu-ranlib $POC " to reproduce this bug. This bug was discovered by NTU Cyber-Security-Lab, for fuzzing research work. If you have any questions, please let me know.
Thanks for the report. Proposed fix posted:
Author: Mark Wielaard <firstname.lastname@example.org>
Date: Thu Oct 18 19:01:52 2018 +0200
arlib: Check that sh_entsize isn't zero.
A bogus ELF file could have sh_entsize as zero. Don't divide by zero,
but just assume there are no symbols in the section.
Signed-off-by: Mark Wielaard <email@example.com>
For reference this was assigned CVE-2018-18521.
Note that this bug was not in a generic library, just in the code shared by the eu-ar and eu-ranlib binaries.
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