Re: [PATCH v3] erofs: cap LZMA stream pool size

[Gao Xiang <hsiangkao@linux.alibaba.com>]

On 2026/7/14 19:47, Michael Bommarito wrote:
> fs/erofs/decompressor_lzma.c sizes the module-global MicroLZMA stream
> pool from num_possible_cpus() when the lzma_streams module parameter is
> unset, then z_erofs_load_lzma_config() preallocates one image-supplied
> dictionary per stream, accepting dictionaries up to 8 MiB.  On high-CPU
> systems, a small EROFS image can pin hundreds of MiB of vmalloc-backed
> decoder state until the erofs module is unloaded.
> 
> Impact: an attacker-supplied EROFS image mounted by the system can pin up
> to 8 MiB times the LZMA stream count of kernel vmalloc memory.
> 
> Bound the default stream count by a new
> CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS option, default 16, so the
> worst-case default preallocation is 128 MiB while preserving the existing
> per-image dictionary limit.  An explicit lzma_streams module parameter is
> still honoured as-is, so administrators who deliberately size the pool are
> not affected.
> 
> Fixes: 622ceaddb764 ("erofs: lzma compression support")
> Cc: stable@vger.kernel.org
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>

Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Thanks,
Gao Xiang