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


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,
>>
> 
> 


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