[PATCH v3 2/2] erofs-utils: lib/tar: reject negative size= value in PAX header

[Gao Xiang]

On 2026/3/16 15:58, Utkal Singh wrote:
> The PAX extended header size= field is parsed into a signed long
> long but no check is made for negative values before assigning to
> eh->st.st_size. A crafted PAX header with size=-1 passes the
> existing format check, resulting in a negative file size that can
> cause incorrect memory allocation and heap corruption in subsequent
> read or seek operations.
> 
> Add an explicit check to reject negative size= values with -EINVAL.
> 
> Reproducer (base64-encoded minimal crafted tar):
>    echo "Li9QYXhIZWFkZXJzL3Rlc3QAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAADAwMDA2NjYAMDAwMDAwMAAwMDAwMDAwADAwMDAwMDAwMDEzADAwMDAwMDAwMDAwADAxMTA3NgAgeAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAB1c3RhciAgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAxMyBzaXplPS0xCgAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=" | base64 -d > crafted-negative-size.tar
>    mkfs.erofs --tar=f out.img < crafted-negative-size.tar

please just follow the format like this, you need to compress it
to avoid too long message:

commit ab858f291a1a
Author: Gao Xiang <hsiangkao at linux.alibaba.com>
Date:   Wed Sep 24 15:17:46 2025 +0800

     erofs-utils: dump: avoid SIGSEGV when time cannot be represented

     Just show the raw time in seconds since the UNIX epoch instead.

     Reproducible image (base64-encoded gzipped blob):
     H4sICACa02gAA3JlcHJvAGNgGAWjYBSMVPDo4dcHvU4WITpANg+DCgM7VPwFM0INE5L6OzNL
     tafaus7ZdHvpkTy+2l3o5rGjCxAAIGsOODIzlDD8/v//P0gEQsKACphkZAG5QgUqFgpka0LZ
     4QyMDKpQdgJQPAzKTgWKR0LZWUjsfE4oIydVLzk/JyUtMyfVAEQYgggjEGGMbD/QYoa3jYwM
     KUCaA+y6//8ZkeSLK6uyE3NyUovQGaz/YfZgSJHKwBd+YPc5MjHYQvkg94HiK6KjuRHE14OK
     GyCFnyGQbQhlGwPDJhjKtgDGnp6eHiJIkPwvxYIwHylpoPmfiQq+RWcwk69dUJcG7hllDHUG
     I7oIKEPDRcTe7jqNqesp5bYzYs0ydGCACy4gwJC6xEWZyWxQH2FVgyifQKW3OlL5xMLAAi8/
     9EtyC/SBGnQzcxPTU9NT84yMjM0MTAwMTI30wQURhMQo9/7Ayz8OcPnEhWQ+K46yko2RjaEi
     saSkyLCCgQFIwvlGEBKpxA3elv8GrIcJXP4xMWgoQ8wARSLY2zgqOkYoZgLTIJYGM3aVo2AU
     jIJRMLAAABdVKPsAEAAA


Thanks,
Gao Xiang