Re: [PATCH] mm: fix protection of mm_struct fields in get_cmdline()

[Konstantin Khlebnikov]

On 15.05.2019 11:22, Oscar Salvador wrote:
> On Wed, May 15, 2019 at 11:15:37AM +0300, Konstantin Khlebnikov wrote:
> > Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|
> > end and env_start|end in mm_struct") related mm fields are protected with
> > separate spinlock and mmap_sem held for read is not enough for protection.
> >
> > Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct")
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
>
> This was already addressed by [1]?

Yep.

> [1] https://patchwork.kernel.org/patch/10923003/
>
> > ---
> >   mm/util.c |    4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/util.c b/mm/util.c
> > index e2e4f8c3fa12..540e7c157cf2 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -717,12 +717,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen)
> >   	if (!mm->arg_end)
> >   		goto out_mm;	/* Shh! No looking before we're done */
> >   
> > -	down_read(&mm->mmap_sem);
> > +	spin_lock(&mm->arg_lock);
> >   	arg_start = mm->arg_start;
> >   	arg_end = mm->arg_end;
> >   	env_start = mm->env_start;
> >   	env_end = mm->env_end;
> > -	up_read(&mm->mmap_sem);
> > +	spin_unlock(&mm->arg_lock);
> >   
> >   	len = arg_end - arg_start;
> >