svn commit: r295359 - head/sys/fs/fdescfs

[Bruce Evans]

On Sun, 7 Feb 2016, Pedro F. Giffuni wrote:

> Log:
>  fdesc_setattr: unitialized pointer read
>
>  CID:	1018688

Bug in Coverity.

> Modified: head/sys/fs/fdescfs/fdesc_vnops.c
> ==============================================================================
> --- head/sys/fs/fdescfs/fdesc_vnops.c	Sun Feb  7 01:04:47 2016	(r295358)
> +++ head/sys/fs/fdescfs/fdesc_vnops.c	Sun Feb  7 01:09:38 2016	(r295359)
> @@ -465,7 +465,7 @@ fdesc_setattr(ap)
> {
> 	struct vattr *vap = ap->a_vap;
> 	struct vnode *vp;
> -	struct mount *mp;
> +	struct mount *mp = NULL;
> 	struct file *fp;
> 	struct thread *td = curthread;
> 	cap_rights_t rights;

2 style bugs in the caller to hide the Coverity bug:
- initialization in declaration
- unused initialization

The initialization is done by calling vn_start_write(... &mp, flags).
mp is only an output parameter unless (flags & V_MNTREF), and fdesc
doesn't put V_MNTREF in flags.

This is a common way of returning extra values so it shouldn't cause
warning is the source code doesn't have bogus initializations in the
caller.  Compilers that look at only 1 source file at a time can't see
the full API so they have to assume that such parameters are output-only
if they are uninitialized in callers.  Checkers need to understand the
API if they want to do more.

Bruce