Oleg Nesterov <[email protected]> writes: > de_thread() waits for other threads with ->cred_guard_mutex held and this > is really bad because the time is not bounded, debugger can delay the exit > and this lock has a lot of users (mostly abusers imo) in fs/proc and more. > And this leads to deadlock if debugger tries to take the same mutex:
Oleg. I looked at the history in proc of users of cred_guard_mutex and the proc users are grabbing cred_guard_mutex for the proper semantic reasons. To avoid races with setuid exec that could result in an information disclosure. I do agree that a mutex is the wrong data structure for the job cred_guard_mutex is performing. The job of sorting ensuring debuggers and proc processes see either the old version or the new version of the task. I need to play with the code but I suspect the best we can handle this preventing both security issues and problems in the future is to create a new task struct and populate it appropriate with the new data from exec (at least in the case of setuid exec). I am thinking of generalizing the case of a non-leader exec where we have to assume the leaders pid. I don't yet know what the performance implications would be but that would clean the users up a lot. On that score I believe we can incrementally approach that point and only grab the cred_guard_mutex in exec if we are performing an exec that changes the processes credentials. Right now I don't think it introduces any new security information disclosures but the moving of flush_signal_handlers outside of cred_guard_mutex feels wrong. Eric
