linux-cve-announce - CVE-2025-22070: fs/9p: fix NULL pointer dereference on mkdir

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Message-ID: <2025041610-CVE-2025-22070-4509@gregkh>
Date: Wed, 16 Apr 2025 16:12:41 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-22070: fs/9p: fix NULL pointer dereference on mkdir

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

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

fs/9p: fix NULL pointer dereference on mkdir

When a 9p tree was mounted with option 'posixacl', parent directory had a
default ACL set for its subdirectories, e.g.:

  setfacl -m default:group:simpsons:rwx parentdir

then creating a subdirectory crashed 9p client, as v9fs_fid_add() call in
function v9fs_vfs_mkdir_dotl() sets the passed 'fid' pointer to NULL
(since dafbe689736) even though the subsequent v9fs_set_create_acl() call
expects a valid non-NULL 'fid' pointer:

  [   37.273191] BUG: kernel NULL pointer dereference, address: 0000000000000000
  ...
  [   37.322338] Call Trace:
  [   37.323043]  <TASK>
  [   37.323621] ? __die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434)
  [   37.324448] ? page_fault_oops (arch/x86/mm/fault.c:714)
  [   37.325532] ? search_module_extables (kernel/module/main.c:3733)
  [   37.326742] ? p9_client_walk (net/9p/client.c:1165) 9pnet
  [   37.328006] ? search_bpf_extables (kernel/bpf/core.c:804)
  [   37.329142] ? exc_page_fault (./arch/x86/include/asm/paravirt.h:686 arch/x86/mm/fault.c:1488 arch/x86/mm/fault.c:1538)
  [   37.330196] ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:574)
  [   37.331330] ? p9_client_walk (net/9p/client.c:1165) 9pnet
  [   37.332562] ? v9fs_fid_xattr_get (fs/9p/xattr.c:30) 9p
  [   37.333824] v9fs_fid_xattr_set (fs/9p/fid.h:23 fs/9p/xattr.c:121) 9p
  [   37.335077] v9fs_set_acl (fs/9p/acl.c:276) 9p
  [   37.336112] v9fs_set_create_acl (fs/9p/acl.c:307) 9p
  [   37.337326] v9fs_vfs_mkdir_dotl (fs/9p/vfs_inode_dotl.c:411) 9p
  [   37.338590] vfs_mkdir (fs/namei.c:4313)
  [   37.339535] do_mkdirat (fs/namei.c:4336)
  [   37.340465] __x64_sys_mkdir (fs/namei.c:4354)
  [   37.341455] do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83)
  [   37.342447] entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

Fix this by simply swapping the sequence of these two calls in
v9fs_vfs_mkdir_dotl(), i.e. calling v9fs_set_create_acl() before
v9fs_fid_add().

The Linux kernel CVE team has assigned CVE-2025-22070 to this issue.


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

	Issue introduced in 6.0 with commit dafbe689736f62c696ac64809b17bdc752cfbe76 and fixed in 6.12.23 with commit 8522051c58d68146b93e8a5ba9987e83b3d64e7b
	Issue introduced in 6.0 with commit dafbe689736f62c696ac64809b17bdc752cfbe76 and fixed in 6.13.11 with commit 2139dea5c53e3bb63ac49a6901c85e525a80ee8a
	Issue introduced in 6.0 with commit dafbe689736f62c696ac64809b17bdc752cfbe76 and fixed in 6.14.2 with commit 6517b395cb1e43fbf3962dd93e6fb4a5e5ab100e
	Issue introduced in 6.0 with commit dafbe689736f62c696ac64809b17bdc752cfbe76 and fixed in 6.15-rc1 with commit 3f61ac7c65bdb26accb52f9db66313597e759821

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-2025-22070
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/9p/vfs_inode_dotl.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/8522051c58d68146b93e8a5ba9987e83b3d64e7b
	https://git.kernel.org/stable/c/2139dea5c53e3bb63ac49a6901c85e525a80ee8a
	https://git.kernel.org/stable/c/6517b395cb1e43fbf3962dd93e6fb4a5e5ab100e
	https://git.kernel.org/stable/c/3f61ac7c65bdb26accb52f9db66313597e759821