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Bug 1064825 - gcc address sanitizer reports global-buffer-overflow when compiled with optimization
Summary: gcc address sanitizer reports global-buffer-overflow when compiled with optim...
Keywords:
Status: CLOSED UPSTREAM
Alias: None
Product: Fedora
Classification: Fedora
Component: gcc
Version: 20
Hardware: x86_64
OS: Linux
unspecified
medium
Target Milestone: ---
Assignee: Jakub Jelinek
QA Contact: Fedora Extras Quality Assurance
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2014-02-13 11:32 UTC by Thomas Sondergaard
Modified: 2014-02-13 17:29 UTC (History)
2 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Environment:
Last Closed: 2014-02-13 17:29:35 UTC


Attachments (Terms of Use)
Example that shows the problem (deleted)
2014-02-13 11:32 UTC, Thomas Sondergaard
no flags Details


Links
System ID Priority Status Summary Last Updated
GNU Compiler Collection 60183 None None None Never

Description Thomas Sondergaard 2014-02-13 11:32:45 UTC
Created attachment 862746 [details]
Example that shows the problem

Description of problem:
asan_symbolizer reports global-buffer-overflow in asan_bug/d3des.c:376, but only when compiled with optimization

Version-Release number of selected component (if applicable):
gcc (GCC) 4.8.2 20131212 (Red Hat 4.8.2-7)

Also present in gcc (GCC) 4.8.1 20130715 (Red Hat 4.8.1-4) from rhel6 devtoolset-2.

How reproducible:
Fully reproducible

Steps to Reproduce:
1. untar attachment
2. make sure you have asan_symbolize.py from llvm/clang in path
3. run make
4. Modify Makefile to disable optimization (remove -O2)
5. run make

Actual results:
asan reports global-buffer-overflow in asan_bug/d3des.c:376 when optimization is enabled and doesn't when optimization is disabled

Expected results:
asan results should be consistent independent of optimization levels. The d3des.{h,c} files I have from realvnc, but tigervnc and several other realvnc derived projects use the same. As far as I can see the code does not overflow the buffer.

The code in d3des.c around line 376 looks like this:
    
    unsigned long keys = KnL; // via function parameter
    for( round = 0; round < 8; round++ ) {
      ...
      work ^= *keys++;
      ...
      work  = right ^ *keys++;
      ...
      work ^= *keys++;
      ...
      work  = leftt ^ *keys++;  // *** d3des.c Line 376 ***
      ...
    }
    
In the eight iteration of the loop immediately after line 376, keys will have been incremented 32 times and is thus one past the end of KnL, but while post-increment (++) has higher precedence than dereference (*) it is a post-increment, so it is not dereferenced after being past the end.

So it looks to me like the address sanitizer is reporting a false positive or the compiler is generating incorrect code.

Comment 1 Thomas Sondergaard 2014-02-13 11:39:09 UTC
Problem is not reproducible when compiled with clang from Fedora 20, regardless of optimization.

clang version 3.3 (tags/RELEASE_33/final)

Comment 2 Jakub Jelinek 2014-02-13 17:29:35 UTC
Tracking this upstream as http://gcc.gnu.org/PR60183 .


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