CVE-2026-98840 PUBLISHED

vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF

Assigner: Linux
Reserved: 25.09.2026 Published: 18.10.2026 Updated: 18.10.2026

In the Linux kernel, the following vulnerability has been resolved:

vc_screen: reload vc pointer before if (ret) in vcs_write() to avoid UAF

The reload of 'vc' added by commit 8fb9ea65c9d1 ("vc_screen: reload load of struct vc_data pointer in vcs_write() to avoid UAF") sits after the 'if (ret)' block, so the copy-failure break path exits the loop without reloading vc. If the vc was kfree()'d via vc_port_destruct during the unlocked copy_from_user() window, the post-loop 'if (written && vc) vcs_scr_updated(vc)' is reached with a stale non-NULL vc. The '&& vc' guard from commit a287620312dc ("vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write") only handles the NULL case, not this stale-non-NULL case; vcs_notifier() then reads param->vc->vc_num from freed memory:

BUG: KASAN: slab-use-after-free in vcs_notifier+0x7c/0xd0 Read of size 2 at addr ffff888007149190 Call Trace: vcs_notifier+0x7c/0xd0 atomic_notifier_call_chain+0x70/0xa0 vcs_scr_updated+0x77/0xa0 vcs_write+0x71b/0x7e0 Allocated by task: vc_allocate -> con_install -> tty_open Freed by task: kfree <- vt_ioctl (VT_DISALLOCATE -> vc_port_destruct)

Move the reload to immediately after console_lock(), before 'if (ret)', so every break path below passes a fresh vc to the post-loop vcs_scr_updated().

Product Status

Vendor Linux
Product Linux
Versions Default: unaffected
  • affected from 73049768ad57145acd337102c5aa3c788e6642c8 to 1485a3dd97ab1af2605243cabe6b604546d46dd1 (excl.)
  • affected from 7cc3dd79777f6ae4625ec37e84dd18a26dc88bde to 233a2e190b12884d186027d0b86d43a48799b69c (excl.)
  • affected from a287620312dc6dcb9a093417a0e589bf30fcf38a to 9dfcadc5e003fb250dd471db90144bd5366140e9 (excl.)
  • affected from a287620312dc6dcb9a093417a0e589bf30fcf38a to 226bd5603371cd9f6642cbb9e9a677f445de3530 (excl.)
  • Version 43a6281790273c1b0a9ab76609ff0245b968f1e6 is affected
  • Version b6bbb85cf45bf0b070e741997fe0af3a772c5ad5 is affected
  • Version ff4806202749a51938236214adc0281481a57366 is affected
  • Version 8232fca738011ca2ec865b46ec721d1796dc0580 is affected
  • Version 74be188eb2dc1c99d63986167b9a67d415fe7326 is affected
  • Version 09a43e81279b8da15526da09877134b8bcf618b0 is affected
  • affected from 6.12.95 to 6.12.113 (excl.)
  • affected from 6.18.37 to 6.18.56 (excl.)
  • affected from 5.10.260 to 5.11 (excl.)
  • affected from 5.15.211 to 5.16 (excl.)
  • affected from 6.1.177 to 6.2 (excl.)
  • affected from 6.6.144 to 6.7 (excl.)
  • affected from 7.0.14 to 7.1 (excl.)
  • affected from 7.1.2 to 7.2 (excl.)
Vendor Linux
Product Linux
Versions Default: affected
  • Version 7.2 is affected
  • unaffected from 0 to 7.2 (excl.)
  • unaffected from 6.12.113 to 6.12.* (incl.)
  • unaffected from 6.18.56 to 6.18.* (incl.)
  • unaffected from 7.2.10 to 7.2.* (incl.)
  • unaffected from 7.3-rc6 to * (incl.)

References