vt: skip screen update for DEC alignment test on backgroup consoles
Summary
| CVE | CVE-2026-98838 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-18 16:17:38 UTC |
| Updated | 2026-10-21 13:21:49 UTC |
| Description | In the Linux kernel, the following vulnerability has been resolved: vt: skip screen update for DEC alignment test on backgroup consoles [BUG] Recently, we encountered a KASAN warning as follows: BUG: KASAN: slab-out-of-bounds in fb_pad_aligned_buffer+0x11f/0x140 Read of size 1 at addr ff1100015fd9f6a4 by task tty_fbcon_oob/1239 CPU: 7 UID: 0 PID: 1239 Comm: tty_fbcon_oob Not tainted 7.3.0-rc1 #100 PREEMPT(full) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014 Call Trace: <TASK> ... kasan_report+0xf0/0x120 fb_pad_aligned_buffer+0x11f/0x140 ccw_putcs+0x86c/0xa80 fbcon_putcs+0x338/0x410 do_update_region+0x21d/0x450 do_con_write+0x1e0e/0x4880 con_write+0x13/0x80 n_tty_write+0x374/0x1010 file_tty_write.isra.0+0x404/0x7a0 ... reproduce: 1) open /dev/tty0, set a KDFONTOP ioctl with op.op = KD_FONT_OP_SET, op.width = 8 and op.height = 16 (visible VC1) 2) open /dev/tty1, set a KDFONTOP ioctl with op.op = KD_FONT_OP_SET, op.width = 28 and op.height = 24 (invisible VC2) 3) echo 3 > /sys/devices/virtual/graphics/fbcon/rotate_all 4) write EShash8(esc hash8) to tty1 [CAUSE] All VCs render to the framebuffer. setfont only modifies the target VC's font without resizing the framebuffer backing buffer (par->rotated.buf); the buffer is only resized for the visible VC (fbcon_do_set_font -> ... -> vc_do_resize -> update_screen). This relies on the con_should_update() check performed before every update_region(). However, the ESC # 8 path (do_con_trol -> do_update_region) omits the con_should_update() check. After changing the font size of an invisible VC, do_update_region() fills using the new font size against a buffer that was never resized, causing an out-of-bounds access. [FIX] Only push the update when the console is visible and not blanked, add the con_should_update() check in the do_con_trol() like every other call site of do_update_region() (update_region(), invert_screen(), ...). |
Risk And Classification
EPSS: 0.001680000 probability, percentile 0.057420000 (date 2026-10-21)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 2fc4e71aefab57c80ccc9775aad2af503fc90810 git | Not specified |
| CNA | Linux | Linux | affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 985c000b046ca4ee11ee34ef85db500c569ef6e8 git | Not specified |
| CNA | Linux | Linux | affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 ad06f7312d3f615dd466483ce81a9b9619166686 git | Not specified |
| CNA | Linux | Linux | affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 0ee53081425a1a31ce15089012cd96b8353eb44e git | Not specified |
| CNA | Linux | Linux | affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 0928ed9bd7946baee911efa401088697836e3b1e git | Not specified |
| CNA | Linux | Linux | affected 2.6.12 | Not specified |
| CNA | Linux | Linux | unaffected 2.6.12 semver | Not specified |
| CNA | Linux | Linux | unaffected 6.6.160 6.6.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.12.113 6.12.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.18.56 6.18.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.2.10 7.2.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.3 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/ad06f7312d3f615dd466483ce81a9b9619166686 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/985c000b046ca4ee11ee34ef85db500c569ef6e8 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/0928ed9bd7946baee911efa401088697836e3b1e | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/0ee53081425a1a31ce15089012cd96b8353eb44e | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/2fc4e71aefab57c80ccc9775aad2af503fc90810 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.