CVE-2026-98636: squashfs: Add dictionary size range check to prevent shift-out-of-bounds

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

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

squashfs: Add dictionary size range check to prevent shift-out-of-bounds

When an abnormal SquashFS image (COMP_OPTS flag is 1 but dictionary size
is 0) is mounted, and performs shift operations using dictionarysize, the
shift exponent is -1, causing a shift-out-of-bounds.

Detail as below:
squashfs_comp_opts(msblk, buffer, length)
  squashfs_xz_comp_opts()
    if (comp_opts)
      n = ffs(opts->dict_size) - 1;<----opts->dict_size=0, n=-1
      if (opts->dict_size != (1 << n) && opts->dict_size !=
	  	(1 << n) + (1 << (n + 1))) <----shift-out-of-bounds

Fix it by adding a dictionary size range check before the shift operation.

The Linux kernel CVE team has assigned CVE-2026-98636 to this issue.


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

	Issue introduced in 2.6.39 with commit ff750311d30acc9564ef577050794953eee59f01 and fixed in 5.10.271 with commit b02948a23455f8190a53887b2d2c13ae1d360cea
	Issue introduced in 2.6.39 with commit ff750311d30acc9564ef577050794953eee59f01 and fixed in 5.15.222 with commit 9d9c5c218ea356a1d88765214ad2919605280ab1
	Issue introduced in 2.6.39 with commit ff750311d30acc9564ef577050794953eee59f01 and fixed in 6.1.189 with commit 7a1c293e7aa17f1afaee0684e0e931fe23a5a6b1
	Issue introduced in 2.6.39 with commit ff750311d30acc9564ef577050794953eee59f01 and fixed in 6.6.158 with commit c68e0068a236f9a7dfc19720bdf11e5d80a85089
	Issue introduced in 2.6.39 with commit ff750311d30acc9564ef577050794953eee59f01 and fixed in 6.12.112 with commit 88c673a0bd233df44ca0020da82f4fd3876de27a
	Issue introduced in 2.6.39 with commit ff750311d30acc9564ef577050794953eee59f01 and fixed in 6.18.55 with commit 0cb85377daaefb4ce5ce72975f2deb27ee0e0cad
	Issue introduced in 2.6.39 with commit ff750311d30acc9564ef577050794953eee59f01 and fixed in 7.2.9 with commit e1ca4e3a380ef3e8f46ce006f1146392e3f32c98
	Issue introduced in 2.6.39 with commit ff750311d30acc9564ef577050794953eee59f01 and fixed in 7.3-rc5 with commit 1f7745fb3580152ca902ef181b605f33cabfb1d0

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-2026-98636
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/squashfs/xz_wrapper.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/b02948a23455f8190a53887b2d2c13ae1d360cea
	https://git.kernel.org/stable/c/9d9c5c218ea356a1d88765214ad2919605280ab1
	https://git.kernel.org/stable/c/7a1c293e7aa17f1afaee0684e0e931fe23a5a6b1
	https://git.kernel.org/stable/c/c68e0068a236f9a7dfc19720bdf11e5d80a85089
	https://git.kernel.org/stable/c/88c673a0bd233df44ca0020da82f4fd3876de27a
	https://git.kernel.org/stable/c/0cb85377daaefb4ce5ce72975f2deb27ee0e0cad
	https://git.kernel.org/stable/c/e1ca4e3a380ef3e8f46ce006f1146392e3f32c98
	https://git.kernel.org/stable/c/1f7745fb3580152ca902ef181b605f33cabfb1d0