Re: [patch] vga_switcheroo: comparing too few characters instrncmp()

[Mailing Lists]

On Fri, 2011-01-07 at 07:30 +0200, Alexey Dobriyan wrote:
> On Fri, Jan 07, 2011 at 08:12:27AM +0300, Dan Carpenter wrote:
> > This is a copy-and-paste bug.  We should be comparing 4 characters here
> > instead of 3.
> 
> > --- a/drivers/gpu/vga/vga_switcheroo.c
> > +++ b/drivers/gpu/vga/vga_switcheroo.c
> > @@ -346,11 +346,11 @@ vga_switcheroo_debugfs_write(struct file *filp, const char __user *ubuf,
> >  	if (strncmp(usercmd, "DIS", 3) == 0)
> >  		client_id = VGA_SWITCHEROO_DIS;
> >  
> > -	if (strncmp(usercmd, "MIGD", 3) == 0) {
> > +	if (strncmp(usercmd, "MIGD", 4) == 0) {
> >  		just_mux = true;
> >  		client_id = VGA_SWITCHEROO_IGD;
> >  	}
> > -	if (strncmp(usercmd, "MDIS", 3) == 0) {
> > +	if (strncmp(usercmd, "MDIS", 4) == 0) {
> 
> How about you NUL-terminate, and use strcmp().

Userspace data? How to guarantee NULL terminated string at runtime? 

Still, the string constants being compared against are already NULL
terminated, so he could use strcmp as is.

Also, strcmp() would discard user strings that start with a matching
substring ("DIS", "DISK", "DISH", "DISINTERESTED" would all set
client_id to VGA_SWITCHEROO_DIS, using strncmp(), but strcmp() would
only match "DIS").

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