Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old_exec

[Eric W. Biederman]

Bernd Edlinger <bernd.edlinger@xxxxxxxxxx> writes:

> On 3/9/20 8:58 PM, Eric W. Biederman wrote:
>> 
>> Ok.  I think this has it sorted:
>> 
>>     exec: Move exec_mmap right after de_thread in flush_old_exec
>>     
>>     I have read through the code in exec_mmap and I do not see anything
>>     that depends on sighand or the sighand lock, or on signals in anyway
>>     so this should be safe.
>>     
>>     This rearrangement of code has two significant benefits.  It makes
>>     the determination of passing the point of no return by testing bprm->mm
>>     accurate.  All failures prior to that point in flush_old_exec are
>>     either truly recoverable or they are fatal.
>>     
>>     Further this consolidates all of the possible indefinite waits for
>>     userspace together at the top of flush_old_exec.  The possible wait
>>     for a ptracer on PTRACE_EVENT_EXIT, the possible wait for a page fault
>>     to be resolved in clear_child_tid, and the possible wait for a page
>>     fault in exit_robust_list.
>>     
>>     This consolidation allows the creation of a mutex to replace
>>     cred_guard_mutex that is not held over possible indefinite userspace
>>     waits.  Which will allow removing deadlock scenarios from the kernel.
>>     
>>     Reviewed-by: Bernd Edlinger <bernd.edlinger@xxxxxxxxxx>
>>     Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
>> 
>> 
>> I don't think I usually have this many typos.  Sigh.
>> 
>
> OK.
>
> never mind,

No no.  I really appreciate all of the scrutiny.  Frequently the issues
that will produce typos or poor patch descriptions are also the issues
that will produce sloppy patches as well.  I was just frustrated with
myself.

Eric