linux-kernel - Re: [PATCH] x86: Fix io_bitmap_ptr memory leak on copy

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Date:	Thu, 10 Feb 2011 19:07:47 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	Tadashi Abe <tabe@...sta.com>
cc:	x86@...nel.org, tglx@...utronix.de, hpa@...or.com,
	mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: Fix io_bitmap_ptr memory leak on copy_process()

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@...sta.com>
> ---
>  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..

>  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@...osbits.net>            http://www.chaosbits.net/
Plain text mails only, please.
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html

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