Am 06.03.20 um 06:17 schrieb Eric W. Biederman: > Bernd Edlinger <bernd.edlinger@xxxxxxxxxx> writes: > >> On 3/5/20 10:16 PM, Eric W. Biederman wrote: >>> >>> The cred_guard_mutex is problematic. The cred_guard_mutex is held >>> over the userspace accesses as the arguments from userspace are read. >>> The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other >>> threads are killed. The cred_guard_mutex is held over >>> "put_user(0, tsk->clear_child_tid)" in exit_mm(). >>> >>> Any of those can result in deadlock, as the cred_guard_mutex is held >>> over a possible indefinite userspace waits for userspace. >>> >>> Add exec_update_mutex that is only held over exec updating process >>> with the new contents of exec, so that code that needs not to be >>> confused by exec changing the mm and the cred in ways that can not >>> happen during ordinary execution of a process can take. >>> >>> The plan is to switch the users of cred_guard_mutex to >>> exed_udpate_mutex one by one. This lets us move forward while still >>> being careful and not introducing any regressions. >>> >>> Link: https://lore.kernel.org/lkml/20160921152946.GA24210@xxxxxxxxxxxxxx/ >>> Link: https://lore.kernel.org/lkml/AM6PR03MB5170B06F3A2B75EFB98D071AE4E60@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ >>> Link: https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@xxxxxxxxxx/ >>> Link: https://lore.kernel.org/lkml/20160923095031.GA14923@xxxxxxxxxx/ >>> Link: https://lore.kernel.org/lkml/20170213141452.GA30203@xxxxxxxxxx/ >>> Ref: 45c1a159b85b ("Add PTRACE_O_TRACEVFORKDONE and PTRACE_O_TRACEEXIT facilities.") >>> Ref: 456f17cd1a28 ("[PATCH] user-vm-unlock-2.5.31-A2") >>> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> >>> --- >>> fs/exec.c | 4 ++++ >>> include/linux/sched/signal.h | 9 ++++++++- >>> kernel/fork.c | 1 + >>> 3 files changed, 13 insertions(+), 1 deletion(-) >>> >>> diff --git a/fs/exec.c b/fs/exec.c >>> index c243f9660d46..ad7b518f906d 100644 >>> --- a/fs/exec.c >>> +++ b/fs/exec.c >>> @@ -1182,6 +1182,7 @@ static int de_thread(struct linux_binprm *bprm, struct task_struct *tsk) >>> release_task(leader); >>> } >>> >>> + mutex_lock(¤t->signal->exec_update_mutex); And by the way, could you make this mutex_lock_killable? Bernd.
