vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write

Summary

In the Linux kernel, the following vulnerability has been resolved: vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write A KASAN null-ptr-deref was observed in vcs_notifier(): BUG: KASAN: null-ptr-deref in vcs_notifier+0x98/0x130 Read of size 2 at addr qmp_cmd_name: qmp_capabilities, arguments: {} The issue is a race condition in vcs_write(). When the console_lock is temporarily dropped (to copy data from userspace), the vc_data pointer obtained from vcs_vc() may become stale. After re-acquiring the lock, vcs_vc() is called again to re-validate the pointer. If the vc has been deallocated in the meantime, vcs_vc() returns NULL, and the while loop breaks (with written > 0). However, after the loop, vcs_scr_updated(vc) is still called with the now-NULL vc pointer, leading to a null pointer dereference in the notifier chain (vcs_notifier dereferences param->vc). Fix this by adding a NULL check for vc before calling vcs_scr_updated().

Timeline

1. Jul 19, 2026, 11:59 AM UTCCVE published
2. Aug 17, 2026, 4:50 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 5.10.181 · fixed in 5.10.260; From 5.15.113 · fixed in 5.15.211; From 6.1.30 · fixed in 6.1.177; From 4.14.327 · fixed in 4.15; From 4.19.284 · fixed in 4.20; From 5.4.244 · fixed in 5.5; From 6.3.4 · fixed in 6.4

• Linux Linux

  6.4

References 9