From: Yi Yang Date: Thu, 4 Jun 2026 06:07:34 +0000 (+0000) Subject: vc_screen: fix null-ptr-deref in vcs_notifier() during concurrent vcs_write X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=a287620312dc6dcb9a093417a0e589bf30fcf38a;p=thirdparty%2Fkernel%2Flinux.git 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(). Fixes: 8fb9ea65c9d1 ("vc_screen: reload load of struct vc_data pointer in vcs_write() to avoid UAF") Cc: stable@vger.kernel.org Signed-off-by: Yi Yang Reviewed-by: Jiri Slaby Link: https://patch.msgid.link/20260604060734.2914976-1-yiyang13@huawei.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/tty/vt/vc_screen.c b/drivers/tty/vt/vc_screen.c index 4d2d46c95fef..7d40eacc21b3 100644 --- a/drivers/tty/vt/vc_screen.c +++ b/drivers/tty/vt/vc_screen.c @@ -686,7 +686,7 @@ vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos) } *ppos += written; ret = written; - if (written) + if (written && vc) vcs_scr_updated(vc); return ret;