CVE-2025-38215 MEDIUM

In the Linux kernel, the following vulnerability has been resolved: fbdev: Fix do_register_framebuffer to prevent null-ptr-deref in fb_videomode_to_var If fb_add_videomode() in do_register_framebuffer() fails to allocate memory for fb_videomode, it will later lead to a null-ptr dereference in fb_videomode_to_var(), as the fb_info is registered while not having the mode in modelist that is expected to be there, i.e. the one that is described in fb_info->var. ================================================================ general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 1 PID: 30371 Comm: syz-executor.1 Not tainted 5.10.226-syzkaller #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 RIP: 0010:fb_videomode_to_var+0x24/0x610 drivers/video/fbdev/core/modedb.c:901 Call Trace: display_to_var+0x3a/0x7c0 drivers/video/fbdev/core/fbcon.c:929 fbcon_resize+0x3e2/0x8f0 drivers/video/fbdev/core/fbcon.c:2071 resize_screen drivers/tty/vt/vt.c:1176 [inline] vc_do_resize+0x53a/0x1170 drivers/tty/vt/vt.c:1263 fbcon_modechanged+0x3ac/0x6e0 drivers/video/fbdev/core/fbcon.c:2720 fbcon_update_vcs+0x43/0x60 drivers/video/fbdev/core/fbcon.c:2776 do_fb_ioctl+0x6d2/0x740 drivers/video/fbdev/core/fbmem.c:1128 fb_ioctl+0xe7/0x150 drivers/video/fbdev/core/fbmem.c:1203 vfs_ioctl fs/ioctl.c:48 [inline] __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl fs/ioctl.c:739 [inline] __x64_sys_ioctl+0x19a/0x210 fs/ioctl.c:739 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x67/0xd1 ================================================================ Even though fbcon_init() checks beforehand if fb_match_mode() in var_to_display() fails, it can not prevent the panic because fbcon_init() does not return error code. Considering this and the comment in the code about fb_match_mode() returning NULL - "This should not happen" - it is better to prevent registering the fb_info if its mode was not set successfully. Also move fb_add_videomode() closer to the beginning of do_register_framebuffer() to avoid having to do the cleanup on fail. Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Additional Descriptions (1)

En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: fbdev: Corregir do_register_framebuffer para evitar la desreferencia null-ptr en fb_videomode_to_var Si fb_add_videomode() en do_register_framebuffer() no puede asignar memoria para fb_videomode, más tarde provocará una desreferencia null-ptr en fb_videomode_to_var(), ya que fb_info se registra sin tener el modo en modelist que se espera que esté allí, es decir, el que se describe en fb_info->var. ================================================================ general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] CPU: 1 PID: 30371 Comm: syz-executor.1 Not tainted 5.10.226-syzkaller #0 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 RIP: 0010:fb_videomode_to_var+0x24/0x610 drivers/video/fbdev/core/modedb.c:901 Call Trace: display_to_var+0x3a/0x7c0 drivers/video/fbdev/core/fbcon.c:929 fbcon_resize+0x3e2/0x8f0 drivers/video/fbdev/core/fbcon.c:2071 resize_screen drivers/tty/vt/vt.c:1176 [inline] vc_do_resize+0x53a/0x1170 drivers/tty/vt/vt.c:1263 fbcon_modechanged+0x3ac/0x6e0 drivers/video/fbdev/core/fbcon.c:2720 fbcon_update_vcs+0x43/0x60 drivers/video/fbdev/core/fbcon.c:2776 do_fb_ioctl+0x6d2/0x740 drivers/video/fbdev/core/fbmem.c:1128 fb_ioctl+0xe7/0x150 drivers/video/fbdev/core/fbmem.c:1203 vfs_ioctl fs/ioctl.c:48 [inline] __do_sys_ioctl fs/ioctl.c:753 [inline] __se_sys_ioctl fs/ioctl.c:739 [inline] __x64_sys_ioctl+0x19a/0x210 fs/ioctl.c:739 do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x67/0xd1 ================================================================ Aunque fbcon_init() comprueba previamente si fb_match_mode() en var_to_display() falla, no puede evitar el pánico, ya que fbcon_init() no devuelve un código de error. Considerando esto y el comentario en el código sobre que fb_match_mode() devuelve NULL ("Esto no debería ocurrir"), es mejor evitar el registro de fb_info si su modo no se configuró correctamente. También mueva fb_add_videomode() más cerca del inicio de do_register_framebuffer() para evitar tener que realizar la limpieza en caso de fallo. Encontrado por el Centro de Verificación de Linux (linuxtesting.org) con Syzkaller.

Source	Type	Description
[email protected]	Primary	en CWE-476

• https://git.kernel.org/stable/c/0909b2b49c4546a7a08c80f53d93736b63270827
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/17186f1f90d34fa701e4f14e6818305151637b9e
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/3f2098f4fba7718eb2501207ca6e99d22427f25a
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/908c5bb64f9c4319902b8ca1aa3fef8f83302520
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/d803c4c2a4ac8ce2be6d899d5c7ab0bf7ec355e9
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
  Source: af854a3a-2127-422b-91ae-364da2661108
  Mailing List Third Party Advisory
• https://cert-portal.siemens.com/productcert/html/ssa-082556.html
  Source: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e