Messages in this thread | | | Date | Sun, 17 Mar 2013 18:07:36 +0100 | From | Oleg Nesterov <> | Subject | Re: vfs: lockdep splat with prepare_bprm_creds |
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On 03/16, Al Viro wrote: > > On Fri, Mar 15, 2013 at 07:19:56PM +0100, Oleg Nesterov wrote: > > > Cough... I am shy to disclose my ignorance, but could you explain how > > open_exec()->do_filp_open(MAY_EXEC) can succeed in this case? At least > > acl_permission_check() looks as if open_exec() should fail... > > Umm... point. It might be a false positive, actually - some other > seq_file-based sucker (while chmod +x /proc/self/stack will fail, > chmod +x /proc/vmstat won't) that could be fed to execve(), leading to > 1) kernel_read() from execve() can grab m.lock for *some* seq_file m, > while holding ->cred_guard_mutex
Yes, thanks.
I am wondering if lock_trace() is really useful...
Lets ignore proc_pid_syscall() and proc_pid_personality(). Suppose we change proc_pid_stack()
int proc_pid_stack(...) { ...
save_stack_trace_tsk(task, &trace); if (!ptrace_may_access(task, PTRACE_MODE_ATTACH)) goto return -EPERM;
for (i = 0; i < trace.nr_entries; i++) seq_printf(...);
return 0; }
Sure, without cred_guard_mutex we can race with install_exec_creds(). But is it a problem in practice? In any case lock_trace() can't protect against commit_creds()...
We can even do
task_lock(task); err = __ptrace_may_access(task, mode); if (!err) save_stack_trace_tsk(...); task_unlock(task);
This way task_lock() protects us against exec_mmap(). And even exec_mmap() was already called and the task is going to do install_exec_creds() we can't show the stack of this process "after" exec.
Oleg.
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