[bug report] ovl: detect overlapping layers

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Amir Goldstein,

The patch 0e7f2cccb42a: "ovl: detect overlapping layers" from Apr 18,
2019, leads to the following static checker warning:

	fs/overlayfs/super.c:998 ovl_setup_trap()
	warn: passing a valid pointer to 'PTR_ERR'

fs/overlayfs/super.c
   991  static int ovl_setup_trap(struct super_block *sb, struct dentry *dir,
   992                            struct inode **ptrap, const char *name)
   993  {
   994          struct inode *trap;
   995          int err;
   996  
   997          trap = ovl_get_trap_inode(sb, dir);
   998          err = PTR_ERR(trap);
   999          if (IS_ERR(trap) && err == -ELOOP) {
  1000                  pr_err("overlayfs: conflicting %s path\n", name);
  1001                  return err;
  1002          }
  1003  
  1004          *ptrap = trap;
  1005          return 0;
  1006  }

The warning message is wrong but the code is also wrong.  The
ovl_get_trap_inode() can return ERR_PTR(-ENOMEM) and that would lead to
and Oops when we try to call iput() on it.

regards,
dan carpenter