[PATCH v2] Fix read after xfree in linux_nat_detach

[Philipp Rudo <prudo@linux.vnet.ibm.com>]

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,
-- 
2.8.4