CVE-2024-26798

2024-04-0409:15:08

416baaa9-dc9f-4396-8d5f-8c081fb06d67

web.nvd.nist.gov

linux kernel

fbcon font

vulnerability resolved

system crash

syzkaller

page fault

allocation failure

font data

6.2 Medium

AI Score

Confidence

Low

0.0004 Low

EPSS

Percentile

15.7%

JSON

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

fbcon: always restore the old font data in fbcon_do_set_font()

Commit a5a923038d70 (fbdev: fbcon: Properly revert changes when
vc_resize() failed) started restoring old font data upon failure (of
vc_resize()). But it performs so only for user fonts. It means that the
“system”/internal fonts are not restored at all. So in result, the very
first call to fbcon_do_set_font() performs no restore at all upon
failing vc_resize().

This can be reproduced by Syzkaller to crash the system on the next
invocation of font_get(). It’s rather hard to hit the allocation failure
in vc_resize() on the first font_set(), but not impossible. Esp. if
fault injection is used to aid the execution/failure. It was
demonstrated by Sirius:
BUG: unable to handle page fault for address: fffffffffffffff8
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD cb7b067 P4D cb7b067 PUD cb7d067 PMD 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8007 Comm: poc Not tainted 6.7.0-g9d1694dc91ce #20
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:fbcon_get_font+0x229/0x800 drivers/video/fbdev/core/fbcon.c:2286
Call Trace:
<TASK>
con_font_get drivers/tty/vt/vt.c:4558 [inline]
con_font_op+0x1fc/0xf20 drivers/tty/vt/vt.c:4673
vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline]
vt_ioctl+0x632/0x2ec0 drivers/tty/vt/vt_ioctl.c:752
tty_ioctl+0x6f8/0x1570 drivers/tty/tty_io.c:2803
vfs_ioctl fs/ioctl.c:51 [inline]
…

So restore the font data in any case, not only for user fonts. Note the
later ‘if’ is now protected by ‘old_userfont’ and not ‘old_data’ as the
latter is always set now. (And it is supposed to be non-NULL. Otherwise
we would see the bug above again.)

Affected configurations

Vulners

Node

linuxlinux_kernelRange6.0–5.15.151

linuxlinux_kernelRange5.16.0–6.1.81

linuxlinux_kernelRange6.2.0–6.6.21

linuxlinux_kernelRange6.7.0–6.7.9

linuxlinux_kernelRange6.8.0≥

VendorProductVersionCPE
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linuxlinux_kernel*cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

Vendor	Product	Version	CPE
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	*	cpe:2.3:o:linux:linux_kernel::::::::

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "drivers/video/fbdev/core/fbcon.c"
    ],
    "versions": [
      {
        "version": "ebd6f886aa24",
        "lessThan": "20a4b5214f7b",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "a5a923038d70",
        "lessThan": "2f91a96b892f",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "a5a923038d70",
        "lessThan": "73a6bd68a134",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "a5a923038d70",
        "lessThan": "a2c881413dcc",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "a5a923038d70",
        "lessThan": "00d6a284fcf3",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "drivers/video/fbdev/core/fbcon.c"
    ],
    "versions": [
      {
        "version": "6.0",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "6.0",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15.151",
        "lessThanOrEqual": "5.15.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.1.81",
        "lessThanOrEqual": "6.1.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.6.21",
        "lessThanOrEqual": "6.6.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.7.9",
        "lessThanOrEqual": "6.7.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.8",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]