From: Haren Myneni haren@linux.ibm.com
commit 91cdbb955aa94ee0841af4685be40937345d29b8 upstream.
The kernel handles the NX fault by updating CSB or sending signal to process. In multithread applications, children can open VAS windows and can exit without closing them. But the parent can continue to send NX requests with these windows. To prevent pid reuse, reference will be taken on pid and tgid when the window is opened and release them during window close.
The current code is not releasing the tgid reference which can cause pid leak and this patch fixes the issue.
Fixes: db1c08a740635 ("powerpc/vas: Take reference to PID and mm for user space windows") Cc: stable@vger.kernel.org # 5.8+ Reported-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Haren Myneni haren@linux.ibm.com Reviewed-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/6020fc4d444864fe20f7dcdc5edfe53e67480a1c.camel@lin... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/platforms/powernv/vas-window.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
--- a/arch/powerpc/platforms/powernv/vas-window.c +++ b/arch/powerpc/platforms/powernv/vas-window.c @@ -1093,9 +1093,9 @@ struct vas_window *vas_tx_win_open(int v /* * Process closes window during exit. In the case of * multithread application, the child thread can open - * window and can exit without closing it. Expects parent - * thread to use and close the window. So do not need - * to take pid reference for parent thread. + * window and can exit without closing it. so takes tgid + * reference until window closed to make sure tgid is not + * reused. */ txwin->tgid = find_get_pid(task_tgid_vnr(current)); /* @@ -1339,8 +1339,9 @@ int vas_win_close(struct vas_window *win /* if send window, drop reference to matching receive window */ if (window->tx_win) { if (window->user_win) { - /* Drop references to pid and mm */ + /* Drop references to pid. tgid and mm */ put_pid(window->pid); + put_pid(window->tgid); if (window->mm) { mm_context_remove_vas_window(window->mm); mmdrop(window->mm);