CVE-2025-38214 MEDIUM

In the Linux kernel, the following vulnerability has been resolved: fbdev: Fix fb_set_var to prevent null-ptr-deref in fb_videomode_to_var If fb_add_videomode() in fb_set_var() fails to allocate memory for fb_videomode, later it may 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 ================================================================ The reason is that fb_info->var is being modified in fb_set_var(), and then fb_videomode_to_var() is called. If it fails to add the mode to fb_info->modelist, fb_set_var() returns error, but does not restore the old value of fb_info->var. Restore fb_info->var on failure the same way it is done earlier in the function. 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 fb_set_var para evitar la desreferencia null-ptr en fb_videomode_to_var Si fb_add_videomode() en fb_set_var() no puede asignar memoria para fb_videomode, más tarde puede conducir a 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 ================================================================ El motivo es que fb_info->var se modifica en fb_set_var() y, a continuación, se llama a fb_videomode_to_var(). Si no se logra agregar el modo a fb_info->modelist, fb_set_var() devuelve un error, pero no restaura el valor anterior de fb_info->var. Si falla, restaure fb_info->var de la misma forma que se hizo anteriormente en la función. 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/05f6e183879d9785a3cdf2f08a498bc31b7a20aa
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/1a10d91766eb6ddfd5414e4785611e33a4fe0f9b
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/3ca78032a388a0795201792b36e6fc9b6e6e8eed
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/8a3a2887794b2c8e78b3e5d6e3de724527c9f41b
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/b3071bb463ea1e6c686d0dc9638fc940f2f5cf17
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/ee20216f12d9482cd70e44dae5e7fabb38367c71
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/fab201d72fde38d081e2c5d4ad25595c535b7b22
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://git.kernel.org/stable/c/ff0e037241173b574b385bff53d67567b9816db5
  Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  Patch
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
  Source: af854a3a-2127-422b-91ae-364da2661108
  Mailing List Third Party Advisory
• 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