Subject: CVE-2024-44992: smb/client: avoid possible NULL dereference in cifs_free_subrequest()

From: Greg Kroah-Hartman <[email-masked]>

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

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

smb/client: avoid possible NULL dereference in cifs_free_subrequest()

Clang static checker (scan-build) warning:
	cifsglob.h:line 890, column 3
	Access to field 'ops' results in a dereference of a null pointer.

Commit 519be989717c ("cifs: Add a tracepoint to track credits involved in
R/W requests") adds a check for 'rdata->server', and let clang throw this
warning about NULL dereference.

When 'rdata->credits.value != 0 && rdata->server == NULL' happens,
add_credits_and_wake_if() will call rdata->server->ops->add_credits().
This will cause NULL dereference problem. Add a check for 'rdata->server'
to avoid NULL dereference.

The Linux kernel CVE team has assigned CVE-2024-44992 to this issue.

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

	Issue introduced in 6.10 with commit 69c3c023af25 and fixed in 6.10.7 with commit fead60a6d5f8
	Issue introduced in 6.10 with commit 69c3c023af25 and fixed in 6.11 with commit 74c2ab6d653b

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-2024-44992
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/file.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/fead60a6d5f84b472b928502a42c419253afe6c1
	https://git.kernel.org/stable/c/74c2ab6d653b4c2354df65a7f7f2df1925a40a51