Subject: CVE-2024-26867: comedi: comedi_8255: Correct error in subdevice initialization

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

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

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

comedi: comedi_8255: Correct error in subdevice initialization

The refactoring done in commit 5c57b1ccecc7 ("comedi: comedi_8255: Rework
subdevice initialization functions") to the initialization of the io
field of struct subdev_8255_private broke all cards using the
drivers/comedi/drivers/comedi_8255.c module.

Prior to 5c57b1ccecc7, __subdev_8255_init() initialized the io field
in the newly allocated struct subdev_8255_private to the non-NULL
callback given to the function, otherwise it used a flag parameter to
select between subdev_8255_mmio and subdev_8255_io. The refactoring
removed that logic and the flag, as subdev_8255_mm_init() and
subdev_8255_io_init() now explicitly pass subdev_8255_mmio and
subdev_8255_io respectively to __subdev_8255_init(), only
__subdev_8255_init() never sets spriv->io to the supplied
callback. That spriv->io is NULL leads to a later BUG:

BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 0 P4D 0
Oops: 0010 [#1] SMP PTI
CPU: 1 PID: 1210 Comm: systemd-udevd Not tainted 6.7.3-x86_64 #1
Hardware name: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffa3f1c02d7b78 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffff91f847aefd00 RCX: 000000000000009b
RDX: 0000000000000003 RSI: 0000000000000001 RDI: ffff91f840f6fc00
RBP: ffff91f840f6fc00 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 000000000000005f R12: 0000000000000000
R13: 0000000000000000 R14: ffffffffc0102498 R15: ffff91f847ce6ba8
FS:  00007f72f4e8f500(0000) GS:ffff91f8d5c80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000010540e000 CR4: 00000000000406f0
Call Trace:
 <TASK>
 ? __die_body+0x15/0x57
 ? page_fault_oops+0x2ef/0x33c
 ? insert_vmap_area.constprop.0+0xb6/0xd5
 ? alloc_vmap_area+0x529/0x5ee
 ? exc_page_fault+0x15a/0x489
 ? asm_exc_page_fault+0x22/0x30
 __subdev_8255_init+0x79/0x8d [comedi_8255]
 pci_8255_auto_attach+0x11a/0x139 [8255_pci]
 comedi_auto_config+0xac/0x117 [comedi]
 ? __pfx___driver_attach+0x10/0x10
 pci_device_probe+0x88/0xf9
 really_probe+0x101/0x248
 __driver_probe_device+0xbb/0xed
 driver_probe_device+0x1a/0x72
 __driver_attach+0xd4/0xed
 bus_for_each_dev+0x76/0xb8
 bus_add_driver+0xbe/0x1be
 driver_register+0x9a/0xd8
 comedi_pci_driver_register+0x28/0x48 [comedi_pci]
 ? __pfx_pci_8255_driver_init+0x10/0x10 [8255_pci]
 do_one_initcall+0x72/0x183
 do_init_module+0x5b/0x1e8
 init_module_from_file+0x86/0xac
 __do_sys_finit_module+0x151/0x218
 do_syscall_64+0x72/0xdb
 entry_SYSCALL_64_after_hwframe+0x6e/0x76
RIP: 0033:0x7f72f50a0cb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 47 71 0c 00 f7 d8 64 89 01 48
RSP: 002b:00007ffd47e512d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
RAX: ffffffffffffffda RBX: 0000562dd06ae070 RCX: 00007f72f50a0cb9
RDX: 0000000000000000 RSI: 00007f72f52d32df RDI: 000000000000000e
RBP: 0000000000000000 R08: 00007f72f5168b20 R09: 0000000000000000
R10: 0000000000000050 R11: 0000000000000246 R12: 00007f72f52d32df
R13: 0000000000020000 R14: 0000562dd06785c0 R15: 0000562dcfd0e9a8
 </TASK>
Modules linked in: 8255_pci(+) comedi_8255 comedi_pci comedi intel_gtt e100(+) acpi_cpufreq rtc_cmos usbhid
CR2: 0000000000000000
---[ end trace 0000000000000000 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffa3f1c02d7b78 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffff91f847aefd00 RCX: 000000000000009b
RDX: 0000000000000003 RSI: 0000000000000001 RDI: ffff91f840f6fc00
RBP: ffff91f840f6fc00 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 000000000000005f R12: 0000000000000000
R13: 0000000000000000 R14: ffffffffc0102498 R15: ffff91f847ce6ba8
FS:  00007f72f4e8f500(0000) GS:ffff91f8d5c80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000010540e000 CR4: 00000000000406f0

This patch simply corrects the above mistake by initializing spriv->io
to the given io callback.

The Linux kernel CVE team has assigned CVE-2024-26867 to this issue.

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

	Issue introduced in 6.7 with commit 5c57b1ccecc7 and fixed in 6.7.11 with commit 4a825457a45d
	Issue introduced in 6.7 with commit 5c57b1ccecc7 and fixed in 6.8 with commit cfa9ba1ae0be

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-2024-26867
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:
	drivers/comedi/drivers/comedi_8255.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/4a825457a45d8debc46ab8cba57d47462411710d
	https://git.kernel.org/stable/c/cfa9ba1ae0bef0681833a22d326174fe633caab5