CVE-2024-26798

MEDIUM
Published Apr 4, 2024 Modified Mar 17, 2026 CWE-770

Description

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.)

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CVSS v3.1 Score

5.5
MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-770 CWE-770

Affected Products

Vendor Product
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel

References

Advisories & Patches

https://git.kernel.org/stable/c/00d6a284fcf3fad1b7e1b5bc3cd87cbfb60ce03f https://git.kernel.org/stable/c/20a4b5214f7bee13c897477168c77bbf79683c3d https://git.kernel.org/stable/c/2f91a96b892fab2f2543b4a55740c5bee36b1a6b https://git.kernel.org/stable/c/73a6bd68a1342f3a44cac9dffad81ad6a003e520 https://git.kernel.org/stable/c/a2c881413dcc5d801bdc9535e51270cc88cb9cd8 https://git.kernel.org/stable/c/ae68f57df3335679653868fafccd8c88ef84ae98 https://git.kernel.org/stable/c/00d6a284fcf3fad1b7e1b5bc3cd87cbfb60ce03f https://git.kernel.org/stable/c/20a4b5214f7bee13c897477168c77bbf79683c3d https://git.kernel.org/stable/c/2f91a96b892fab2f2543b4a55740c5bee36b1a6b https://git.kernel.org/stable/c/73a6bd68a1342f3a44cac9dffad81ad6a003e520 https://git.kernel.org/stable/c/a2c881413dcc5d801bdc9535e51270cc88cb9cd8

Frequently Asked Questions

What is CVE-2024-26798? +
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.) It has a CVSS v3.1 base score of 5.5 (MEDIUM).
How severe is CVE-2024-26798? +
CVE-2024-26798 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.
What products are affected by CVE-2024-26798? +
CVE-2024-26798 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2024-26798? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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