Re: [PATCH] x86: Fix io_bitmap_ptr memory leak on copy_process()

[Jesper Juhl]

Small correction to my previous mail below.

On Thu, 10 Feb 2011, Jesper Juhl wrote:

> On Tue, 8 Feb 2011, Tadashi Abe wrote:
> 
> > x86 copy_thread() allocates io_bitmap_ptr area in child's thread_struct
> > when the parent has TIF_IO_BITMAP flag via ioperm().
> > And in this case, if copy_process() terminates with errors
> > after copy_thread() success,
> > this io_bitmap_ptr area is being left without kfree().
> > 
> > Signed-off-by: Tadashi Abe <tabe@xxxxxxxxxx>
> > ---
> >  arch/x86/kernel/process.c |    6 ++++++
> >  include/linux/sched.h     |    5 +++++
> >  kernel/fork.c             |    4 +++-
> >  3 files changed, 14 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> > index b3feabc..290e98b 100644
> > --- a/arch/x86/kernel/process.c
> > +++ b/arch/x86/kernel/process.c
> > @@ -122,6 +122,12 @@ void flush_thread(void)
> >  	clear_used_math();
> >  }
> >  
> > +void free_thread_struct(struct task_struct *p)
> > +{
> > +	if (p->thread.io_bitmap_ptr)
> > +		kfree(p->thread.io_bitmap_ptr);
> 
> kfree(NULL) is perfectly legal, so the 'if' is not needed.
> 
> Why is this a new function? Why not simply call kfree() when needed.
> 
> 
> > +}
> > +
> >  static void hard_disable_TSC(void)
> >  {
> >  	write_cr4(read_cr4() | X86_CR4_TSD);
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 23e9c27..2345391 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -2159,6 +2159,11 @@ extern int copy_thread(unsigned long, unsigned long, unsigned long,
> >  			struct task_struct *, struct pt_regs *);
> >  extern void flush_thread(void);
> >  extern void exit_thread(void);
> > +#ifdef CONFIG_X86
> > +extern void free_thread_struct(struct task_struct *p);
> > +#else
> > +#define free_thread_struct(p) do { } while (0)
> > +#endif
> >  
> 
> This should just go away IMHO.
> 
> >  extern void exit_files(struct task_struct *);
> >  extern void __cleanup_sighand(struct sighand_struct *);
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 25e4291..ffcabf3 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -1179,7 +1179,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> >  		retval = -ENOMEM;
> >  		pid = alloc_pid(p->nsproxy->pid_ns);
> >  		if (!pid)
> > -			goto bad_fork_cleanup_io;
> > +			goto bad_fork_free_thread;
> >  
> >  		if (clone_flags & CLONE_NEWPID) {
> >  			retval = pid_ns_prepare_proc(p->nsproxy->pid_ns);
> > @@ -1315,6 +1315,8 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> >  bad_fork_free_pid:
> >  	if (pid != &init_struct_pid)
> >  		free_pid(pid);
> > +bad_fork_free_thread:
> > +	free_thread_struct(p);
> 
> kfree(p);
>   and be done with it..

I mean kfree(p->thread.io_bitmap_ptr); of course.


> 
> >  bad_fork_cleanup_io:
> >  	if (p->io_context)
> >  		exit_io_context(p);
> > 
> 
> Perhaps I'm overlooking something, in which case I'd be happy to be 
> corrected, but I really can't see why this can't just be as simple as I 
> outlined above.
> 
> 

-- 
Jesper Juhl <jj@xxxxxxxxxxxxx>            http://www.chaosbits.net/
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