Re: [Linux-kernel-mentees] [PATCH] ptrace: Prevent kernel-infoleak in ptrace_get_syscall_info()

[Peilin Ye <yepeilin.cs@gmail.com>]

On Sat, Aug 01, 2020 at 03:21:42AM +0300, Dmitry V. Levin wrote:
> On Mon, Jul 27, 2020 at 05:36:44PM -0400, Peilin Ye wrote:
> > ptrace_get_syscall_info() is copying uninitialized stack memory to
> > userspace due to the compiler not initializing holes in statically
> > allocated structures. Fix it by initializing `info` with memset().
> > 
> > Cc: stable@vger.kernel.org
> > Fixes: 201766a20e30 ("ptrace: add PTRACE_GET_SYSCALL_INFO request")
> > Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
> > Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
> > ---
> >  kernel/ptrace.c | 14 ++++++++------
> >  1 file changed, 8 insertions(+), 6 deletions(-)
> > 
> > diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> > index 43d6179508d6..e48d05b765b5 100644
> > --- a/kernel/ptrace.c
> > +++ b/kernel/ptrace.c
> > @@ -960,15 +960,17 @@ ptrace_get_syscall_info(struct task_struct *child, unsigned long user_size,
> >  			void __user *datavp)
> >  {
> >  	struct pt_regs *regs = task_pt_regs(child);
> > -	struct ptrace_syscall_info info = {
> > -		.op = PTRACE_SYSCALL_INFO_NONE,
> > -		.arch = syscall_get_arch(child),
> > -		.instruction_pointer = instruction_pointer(regs),
> > -		.stack_pointer = user_stack_pointer(regs),
> > -	};
> > +	struct ptrace_syscall_info info;
> >  	unsigned long actual_size = offsetof(struct ptrace_syscall_info, entry);
> >  	unsigned long write_size;
> >  
> > +	memset(&info, 0, sizeof(info));
> > +
> > +	info.op	= PTRACE_SYSCALL_INFO_NONE;
> > +	info.arch = syscall_get_arch(child);
> > +	info.instruction_pointer = instruction_pointer(regs);
> > +	info.stack_pointer = user_stack_pointer(regs);
> > +
> 
> No, please don't do it this way.  If there is a hole in the structure that
> the compiler is unable to initialize properly (and there is a 3-byte hole
> in the beginning indeed), please plug the hole by turning it into
> something that the compiler is capable of initializing.

I see. I will do that and send a v2.

> Also, please do not forget to Cc authors of the commit you are fixing.

Sorry, I forgot about that. Thank you for pointing it out!

Peilin Ye