https://sourceware.org/bugzilla/show_bug.cgi?id=34791
Bug ID: 34791
Summary: GNU ld shifts a 32-bit int by an untrusted
common-symbol alignment power
Product: binutils
Version: 2.46
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: basavesh.shivakumar at wsu dot edu
Target Milestone: ---
Created attachment 17111
--> https://sourceware.org/bugzilla/attachment.cgi?id=17111&action=edit
reproducer
I'm reporting this bug on behalf of my team: Ananta Srikar Puranam, Emily West,
Dr. Swarn Priya, Dr. Peng Gao and Dr. Basavesh Ammanaghatta Shivakumar.
Summary
=======
A crafted x86-64 ET_REL common symbol with alignment power 40 makes current and
released GNU ld evaluate a 32-bit 1 << 40 expression in bfd/elflink.c while
writing a relocatable output symbol, causing deterministic UBSan abort; an
otherwise identical alignment-16 control links cleanly.
Reproduction
============
1. Download and extract
`bfd-common-output-alignment-shift-ubsan-reproducer.tar.gz`.
2. Run the following command with an ld.bfd or all-target `ld-new` binary that
supports the emulation used by the reproducer:
LD_BFD=/path/to/ld-new sh repro.sh
The archive contains the fixed input files, independent controls, helper
scripts needed by `repro.sh`, and their checksums. The script uses a temporary
directory and does not modify the source tree.
Observed result
===============
A crafted x86-64 ET_REL common symbol with alignment power 40 makes current and
released GNU ld evaluate a 32-bit 1 << 40 expression in bfd/elflink.c while
writing a relocatable output symbol, causing deterministic UBSan abort; an
otherwise identical alignment-16 control links cleanly.
Expected result
===============
GNU ld should either produce the correct output or reject the input with a
normal diagnostic. It should not crash, hang, execute undefined behavior, read
outside an input-derived allocation, or produce the described malformed
output.
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