Re: [PATCH] memory:bugxfix panic on cat or write /dev/kmem

[Chenjie (K)]

On 2016/6/23 20:42, Michal Hocko wrote:
> On Fri 24-06-16 01:30:10, chenjie6@xxxxxxxxxx wrote:
> > From: chenjie <chenjie6@xxxxxxxxxx>
> >
> > cat /dev/kmem and echo > /dev/kmem will lead panic
>
> Writing to /dev/kmem without being extremely careful is a disaster AFAIK
> and even reading from the file can lead to unexpected results. Anyway
> I am trying to understand what exactly you are trying to fix here. Why
> writing to/reading from zero pfn should be any special wrt. any other
> potentially dangerous addresses

cat /dev/mem not panic. cat /dev/kmem, just the user's operation for 
nothing.

> > Signed-off-by: chenjie <chenjie6@xxxxxxxxxx>
> > ---
> >   drivers/char/mem.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> > index 71025c2..4bdde28 100644
> > --- a/drivers/char/mem.c
> > +++ b/drivers/char/mem.c
> > @@ -412,6 +412,8 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
> >   			 * by the kernel or data corruption may occur
> >   			 */
> >   			kbuf = xlate_dev_kmem_ptr((void *)p);
> > +			if (!kbuf)
> > +				return -EFAULT;
> >
> >   			if (copy_to_user(buf, kbuf, sz))
> >   				return -EFAULT;
> > @@ -482,6 +484,11 @@ static ssize_t do_write_kmem(unsigned long p, const char __user *buf,
> >   		 * corruption may occur.
> >   		 */
> >   		ptr = xlate_dev_kmem_ptr((void *)p);
> > +		if (!ptr) {
> > +			if (written)
> > +				break;
> > +			return -EFAULT;
> > +		}
> >
> >   		copied = copy_from_user(ptr, buf, sz);
> >   		if (copied) {
> > --
> > 1.8.0
> >
> > --
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