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Re: [PATCH] Fix read after xfree in linux_nat_detach
On Wed, 22 Mar 2017 15:07:22 +0000
Pedro Alves <palves@redhat.com> wrote:
> On 03/22/2017 01:11 PM, Philipp Rudo wrote:
> > At the end of linux_nat_detach there is a check whether the
> > inferior has a fork. If no fork exists the main_lwp is detached
> > (detach_one_lwp) and later, outside the check, deleted
> > (delete_lwp). This is problematic as detach_one_lwp also calls
> > delete_lwp freeing main_lwp. Thus the second call to delete_lwp
> > reads from already freed memory. Fix this by removing delete_lwp
> > at the end of detach_one_lwp.
>
> Why not just move that unconditional call to delete_lwp call at
> the end of linux_nat_detach to the forks_exist_p/true branch?
That was the first idea I had. But I decided that it would be better
for both detach functions (linux_fork_detach and detach_one_lwp) to have
the same behavior and not free the lwp but do that in a separate
step ...
> Actually, that call looks unnecessary for the fork case too,
> since we have:
>
> linux_fork_detach
> -> fork_load_infrun_state
> -> linux_nat_switch_fork
> -> purge_lwp_list
> -> lwp_lwpid_htab_remove_pid
> -> lwp_free
... I obviously missed that.
>
> So... couldn't we just remove that delete_lwp line and be done with
> it?
Looks like we can get simply rid of it. I'll see that I get a test
case running which forks to verify it, tomorrow.
Thanks
Philipp
> Thanks,
> Pedro Alves
>