CVE-2026-98685: smb: client: discard post-EOF pagecache when extending a file via clone range

CVE-2026-98685: smb: client: discard post-EOF pagecache when extending a file via clone range

[Greg Kroah-Hartman]

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

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

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

smb: client: discard post-EOF pagecache when extending a file via clone range

cifs_remap_file_range() discarded the pagecache only for the folios
overlapping the destination region, so when a clone extends the file the
folio straddling the old EOF - which may hold data dirtied past EOF
through an mmap - was never dropped and became visible as file content
once the file was extended.

Start the discard at the smaller of fstart and the old EOF.  i_size is
still old here, so nothing past the old EOF is flushed to the server.

The Linux kernel CVE team has assigned CVE-2026-98685 to this issue.


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

	Issue introduced in 6.7 with commit c54fc3a4f375663f2361a9cbb2955fb4ef912879 and fixed in 7.2.10 with commit 15bb9f1d3e967e328649e92a1451e60a0dc66118
	Issue introduced in 6.7 with commit c54fc3a4f375663f2361a9cbb2955fb4ef912879 and fixed in 7.3-rc6 with commit 4721587f96cb8de8164f3fd203093a0875560999
	Issue introduced in 6.1.68 with commit 358bd5f436d820bb758833050aae065b35d6986c
	Issue introduced in 6.6.7 with commit 43801359c8971cc49b4a4db5015fba77fbd09c32

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-2026-98685
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/smb/client/cifsfs.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/15bb9f1d3e967e328649e92a1451e60a0dc66118
	https://git.kernel.org/stable/c/4721587f96cb8de8164f3fd203093a0875560999