Re: [PATCH v2] Fix read after xfree in linux_nat_detach

[Philipp Rudo <prudo at linux dot vnet dot ibm dot com>]

Hi Pedro,

thanks for pushing.

I think I found the reason the patch didn't apply.  Instead of git send-email I
just copy/pasted this patch to my mail client and it decided that it would be a
good idea to wrap long lines ...

> >> @@ -1549,7 +1549,6 @@ linux_nat_detach (struct target_ops *ops, const
> >> char *args, int from_tty)

Anyway I updated my settings so it shouldn't happen in the future. Thanks for
the hint and sorry for the inconvenience.

Thanks a lot
Philipp


On Tue, 11 Apr 2017 14:31:10 +0100
Pedro Alves <palves@redhat.com> wrote:

> Hi,
> 
> I ran gdb under Valgrind and noticed that this patch hadn't
> been pushed yet.  I've pushed it now.
> 
> FYI, for some reason the patch was corrupt and I had to
> recreate it by hand:
> 
>  $ git am prudo
>  Applying: Fix read after xfree in linux_nat_detach
>  fatal: corrupt patch at line 26
>  Patch failed at 0001 Fix read after xfree in linux_nat_detach
> 
> Thanks,
> Pedro Alves
> 
> On 03/23/2017 01:42 PM, Pedro Alves wrote:
> > OK.
> > 
> > On 03/23/2017 01:17 PM, Philipp Rudo wrote:  
> >> On Wed, 22 Mar 2017 17:26:27 +0000
> >> Pedro Alves <palves@redhat.com> wrote:
> >>  
> >>> On 03/22/2017 05:16 PM, Philipp Rudo wrote:
> >>>  
> >>>> 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.    
> >>>
> >>> This forks handling is the support for the "checkpoint" & 
> >>> friends commands, covered by gdb.base/checkpoint.exp.
> >>> Doesn't seem to exercise detach yet though, unfortunately.  
> >>
> >> I double checked, the same bug also happens when checkpointing.  The
> >> fix now is simply to remove delete_lwp at the end of linux_nat_detach.
> >>
> >> Although testing detach would be good, I'm not sure if the testsuite
> >> would have found this bug.
> >>
> >> ---
> >>
> >> From ee3dced0b22cc1edb10a82aeb79ae35d78d665bc Mon Sep 17 00:00:00 2001
> >> From: Philipp Rudo <prudo@linux.vnet.ibm.com>
> >> Date: Wed, 22 Mar 2017 13:53:50 +0100
> >> Subject: [PATCH v2] Fix read after xfree in linux_nat_detach
> >>
> >> At the end of linux_nat_detach the main_lwp is deleted (delete_lwp).
> >> This is problematic as during detach (detach_one_lwp and
> >> linux_fork_detach) main_lwp already gets freed.  Thus calling
> >> delete_lwp causes a read after free.  Fix it by removing the
> >> unnecessary delete_lwp.
> >>
> >> gdb/ChangeLog:
> >> 	* linux-nat.c (linux_nat_detach): delete_lwp causes read after
> >> free. Remove it.
> >> ---
> >>  gdb/linux-nat.c | 1 -
> >>  1 file changed, 1 deletion(-)
> >>
> >> diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
> >> index dff0da5..efe7daf 100644
> >> --- a/gdb/linux-nat.c
> >> +++ b/gdb/linux-nat.c
> >> @@ -1549,7 +1549,6 @@ linux_nat_detach (struct target_ops *ops, const
> >> char *args, int from_tty) 
> >>        inf_ptrace_detach_success (ops);
> >>      }
> >> -  delete_lwp (main_lwp->ptid);
> >>  }
> >>  
> >>  /* Resume execution of the inferior process.  If STEP is nonzero,
> >>  
> > 
> >   
>