# CVE-2025-38215: fbdev: Fix do_register_framebuffer to prevent null-ptr-deref in fb_videomode_to_var

Status: published. Published: 2025-07-04. Updated: 2026-11-05.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 908c5bb64f9c4319902b8ca1aa3fef8f83302520 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 0909b2b49c4546a7a08c80f53d93736b63270827 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 3f2098f4fba7718eb2501207ca6e99d22427f25a (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < d803c4c2a4ac8ce2be6d899d5c7ab0bf7ec355e9 (affected, git); ≥ 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2; < 17186f1f90d34fa701e4f14e6818305151637b9e (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.12 (affected); ≥ 0; < 2.6.12 (unaffected, semver); ≥ 6.1.143; ≤ 6.1.* (unaffected, semver); ≥ 6.6.95; ≤ 6.6.* (unaffected, semver); ≥ 6.12.35; ≤ 6.12.* (unaffected, semver); ≥ 6.15.4; ≤ 6.15.* (unaffected, semver); ≥ 6.16; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.5; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP: ≥ V3.1.5; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.5; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.17% as of 2026-11-05; percentile 6.29%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/908c5bb64f9c4319902b8ca1aa3fef8f83302520 (CNA: Linux)

- https://git.kernel.org/stable/c/0909b2b49c4546a7a08c80f53d93736b63270827 (CNA: Linux)

- https://git.kernel.org/stable/c/3f2098f4fba7718eb2501207ca6e99d22427f25a (CNA: Linux)

- https://git.kernel.org/stable/c/d803c4c2a4ac8ce2be6d899d5c7ab0bf7ec355e9 (CNA: Linux)

- https://git.kernel.org/stable/c/17186f1f90d34fa701e4f14e6818305151637b9e (CNA: Linux)

- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html (ADP: CVE)

- https://cert-portal.siemens.com/productcert/html/ssa-082556.html (ADP: siemens-SADP)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2025-38215; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2025-38215; retrieved 2026-11-05; source updated Not reported

Revision: 387abe6fe632ec3f42733a21d7aa8adf942cbf490290b0cf6754ddebb8cc4411

Canonical: https://y2.dev/cve/CVE-2025-38215

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