Medium · published July 19, 2026
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().
| Product | Versions | Fixed in |
|---|---|---|
| linux/linux_kernel | ≥ 4.14.327, < 4.15 | 4.15 |
| linux/linux_kernel | ≥ 4.19.284, < 4.20 | 4.20 |
| linux/linux_kernel | ≥ 5.4.244, < 5.5 | 5.5 |
| linux/linux_kernel | ≥ 5.10.181, < 5.10.260 | 5.10.260 |
| linux/linux_kernel | ≥ 5.15.113, < 5.15.211 | 5.15.211 |
| linux/linux_kernel | ≥ 6.1.30, < 6.1.177 | 6.1.177 |
| linux/linux_kernel | ≥ 6.3.4, < 6.4 | 6.4 |
| linux/linux_kernel | ≥ 6.4.1, < 6.6.144 | 6.6.144 |
| linux/linux_kernel | ≥ 6.7, < 6.12.95 | 6.12.95 |
| linux/linux_kernel | ≥ 6.13, < 6.18.37 | 6.18.37 |
| linux/linux_kernel | ≥ 6.19, < 7.0.14 | 7.0.14 |
| linux/linux_kernel | ≥ 7.1, < 7.1.2 | 7.1.2 |
| linux/linux_kernel | all versions | — |
| linux/linux_kernel | all versions | — |
| linux/linux_kernel | all versions | — |
| linux/linux_kernel | all versions | — |
| linux/linux_kernel | all versions | — |
| linux/linux_kernel | all versions | — |