CVE-2026-80892: erofs: cap LZMA stream pool size

CVE-2026-80892: erofs: cap LZMA stream pool size

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

erofs: cap LZMA stream pool size

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 EROFS image mounted by the system can pin up to 8 MiB of
vmalloc memory per LZMA stream, either as intended or unexpectedly.

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 if the number of CPUs is no
less than 16 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.

The Linux kernel CVE team has assigned CVE-2026-80892 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.16 with commit 622ceaddb7649ca328832f50ba1400af778d75fa and fixed in 6.1.184 with commit 682cb3ece37fc5141e73bc726ccf4adb833e5189
	Issue introduced in 5.16 with commit 622ceaddb7649ca328832f50ba1400af778d75fa and fixed in 6.6.151 with commit e8b3d09aa8889dda9be9cbb3d2f0218c4b9acde4
	Issue introduced in 5.16 with commit 622ceaddb7649ca328832f50ba1400af778d75fa and fixed in 6.12.103 with commit 0c676903cb2a61992ded8e7907609cc6b0f11744
	Issue introduced in 5.16 with commit 622ceaddb7649ca328832f50ba1400af778d75fa and fixed in 6.18.44 with commit 5aaa06dfc10f8398c8807453dbec738ea9af10e4
	Issue introduced in 5.16 with commit 622ceaddb7649ca328832f50ba1400af778d75fa and fixed in 7.1.8 with commit e52da169b8c0d19bb2d803f2a07fe0e5a00462d6
	Issue introduced in 5.16 with commit 622ceaddb7649ca328832f50ba1400af778d75fa and fixed in 7.2 with commit c9b47e6b23114e939b17f818471c7a46e59006e7

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-80892
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/erofs/Kconfig
	fs/erofs/decompressor_lzma.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/682cb3ece37fc5141e73bc726ccf4adb833e5189
	https://git.kernel.org/stable/c/e8b3d09aa8889dda9be9cbb3d2f0218c4b9acde4
	https://git.kernel.org/stable/c/0c676903cb2a61992ded8e7907609cc6b0f11744
	https://git.kernel.org/stable/c/5aaa06dfc10f8398c8807453dbec738ea9af10e4
	https://git.kernel.org/stable/c/e52da169b8c0d19bb2d803f2a07fe0e5a00462d6
	https://git.kernel.org/stable/c/c9b47e6b23114e939b17f818471c7a46e59006e7