CVE-2024-26798 (GCVE-0-2024-26798)

Vulnerability from cvelistv5 – Published: 2024-04-04 08:20 – Updated: 2026-05-23 15:37
VLAI
Title
fbcon: always restore the old font data in fbcon_do_set_font()
Summary
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.)
Severity
No CVSS data available.
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2024-04-08 20:53 UTC
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 868749a7456dc48e93887a8474194e2ee6d6c21f , < ae68f57df3335679653868fafccd8c88ef84ae98 (git)
Affected: ebd6f886aa2447fcfcdce5450c9e1028e1d681bb , < 20a4b5214f7bee13c897477168c77bbf79683c3d (git)
Affected: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24 , < 2f91a96b892fab2f2543b4a55740c5bee36b1a6b (git)
Affected: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24 , < 73a6bd68a1342f3a44cac9dffad81ad6a003e520 (git)
Affected: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24 , < a2c881413dcc5d801bdc9535e51270cc88cb9cd8 (git)
Affected: a5a923038d70d2d4a86cb4e3f32625a5ee6e7e24 , < 00d6a284fcf3fad1b7e1b5bc3cd87cbfb60ce03f (git)
Affected: f08ccb792d3eaf1dc62d8cbf6a30d6522329f660 (git)
Affected: 5.15.64 , < 5.15.151 (semver)
Affected: 5.19.6 , < 5.20 (semver)
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Linux Linux Affected: 6.0
Unaffected: 0 , < 6.0 (semver)
Unaffected: 5.15.151 , ≤ 5.15.* (semver)
Unaffected: 6.1.81 , ≤ 6.1.* (semver)
Unaffected: 6.6.21 , ≤ 6.6.* (semver)
Unaffected: 6.7.9 , ≤ 6.7.* (semver)
Unaffected: 6.8 , ≤ * (original_commit_for_fix)
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfbcon: always restore the old font data in fbcon_do_set_font()\n\nCommit a5a923038d70 (fbdev: fbcon: Properly revert changes when\nvc_resize() failed) started restoring old font data upon failure (of\nvc_resize()). But it performs so only for user fonts. It means that the\n\"system\"/internal fonts are not restored at all. So in result, the very\nfirst call to fbcon_do_set_font() performs no restore at all upon\nfailing vc_resize().\n\nThis can be reproduced by Syzkaller to crash the system on the next\ninvocation of font_get(). It\u0027s rather hard to hit the allocation failure\nin vc_resize() on the first font_set(), but not impossible. Esp. if\nfault injection is used to aid the execution/failure. It was\ndemonstrated by Sirius:\n  BUG: unable to handle page fault for address: fffffffffffffff8\n  #PF: supervisor read access in kernel mode\n  #PF: error_code(0x0000) - not-present page\n  PGD cb7b067 P4D cb7b067 PUD cb7d067 PMD 0\n  Oops: 0000 [#1] PREEMPT SMP KASAN\n  CPU: 1 PID: 8007 Comm: poc Not tainted 6.7.0-g9d1694dc91ce #20\n  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014\n  RIP: 0010:fbcon_get_font+0x229/0x800 drivers/video/fbdev/core/fbcon.c:2286\n  Call Trace:\n   \u003cTASK\u003e\n   con_font_get drivers/tty/vt/vt.c:4558 [inline]\n   con_font_op+0x1fc/0xf20 drivers/tty/vt/vt.c:4673\n   vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline]\n   vt_ioctl+0x632/0x2ec0 drivers/tty/vt/vt_ioctl.c:752\n   tty_ioctl+0x6f8/0x1570 drivers/tty/tty_io.c:2803\n   vfs_ioctl fs/ioctl.c:51 [inline]\n  ...\n\nSo restore the font data in any case, not only for user fonts. Note the\nlater \u0027if\u0027 is now protected by \u0027old_userfont\u0027 and not \u0027old_data\u0027 as the\nlatter is always set now. (And it is supposed to be non-NULL. Otherwise\nwe would see the bug above again.)"
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, se resolvi\u00f3 la siguiente vulnerabilidad: fbcon: restaurar siempre los datos de fuentes antiguos en fbcon_do_set_font() commit a5a923038d70 (fbdev: fbcon: revertir correctamente los cambios cuando fall\u00f3 vc_resize()) comenz\u00f3 a restaurar los datos de fuentes antiguos en caso de falla (de vc_resize ()). Pero funciona s\u00f3lo para fuentes de usuario. Significa que las fuentes internas/del \"SYSTEM\" no se restauran en absoluto. Entonces, como resultado, la primera llamada a fbcon_do_set_font() no realiza ninguna restauraci\u00f3n al fallar vc_resize(). Syzkaller puede reproducir esto para bloquear el SYSTEM en la siguiente invocaci\u00f3n de font_get(). Es bastante dif\u00edcil solucionar el error de asignaci\u00f3n en vc_resize() en el primer font_set(), pero no imposible. Esp. si se utiliza la inyecci\u00f3n de fallos para ayudar en la ejecuci\u00f3n/fallo. Sirius lo demostr\u00f3: ERROR: no se puede manejar el error de p\u00e1gina para la direcci\u00f3n: fffffffffffffff8 #PF: acceso de lectura del supervisor en modo kernel #PF: error_code(0x0000) - p\u00e1gina no presente PGD cb7b067 P4D cb7b067 PUD cb7d067 PMD 0 Ups: 0000 [ #1] PREEMPT SMP KASAN CPU: 1 PID: 8007 Comm: poc No contaminado 6.7.0-g9d1694dc91ce #20 Nombre del hardware: PC est\u00e1ndar QEMU (i440FX + PIIX, 1996), BIOS 1.15.0-1 01/04/2014 RIP : 0010:fbcon_get_font+0x229/0x800 drivers/video/fbdev/core/fbcon.c:2286 Seguimiento de llamadas:  con_font_get drivers/tty/vt/vt.c:4558 [en l\u00ednea] con_font_op+0x1fc/0xf20 drivers/tty /vt/vt.c:4673 controladores vt_k_ioctl/tty/vt/vt_ioctl.c:474 [en l\u00ednea] vt_ioctl+0x632/0x2ec0 controladores/tty/vt/vt_ioctl.c:752 tty_ioctl+0x6f8/0x1570 controladores/tty/tty_io. c:2803 vfs_ioctl fs/ioctl.c:51 [en l\u00ednea] ... As\u00ed que restaure los datos de fuente en cualquier caso, no solo para las fuentes del usuario. Tenga en cuenta que el \u0027if\u0027 posterior ahora est\u00e1 protegido por \u0027old_userfont\u0027 y no por \u0027old_data\u0027 ya que este \u00faltimo siempre est\u00e1 configurado ahora. (Y se supone que no es NULL. De lo contrario, volver\u00edamos a ver el error anterior)."
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      "product_status:known_not_affected": "198",
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      "title": "kernel: fbcon: always restore the old font data in fbcon_do_set_font()",
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}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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