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Yi Yang
43a6281790
commita287620312upstream. 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:8fb9ea65c9("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 <yiyang13@huawei.com> Reviewed-by: Jiri Slaby <jirislaby@kernel.org> Link: https://patch.msgid.link/20260604060734.2914976-1-yiyang13@huawei.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>