Re: [PATCH] Add flags option to get xattr method paired to __vfs_getxattr

[Mark Salyzyn <salyzyn@android.com>]

On 8/15/19 3:27 PM, James Morris wrote:
> On Thu, 15 Aug 2019, Mark Salyzyn wrote:
>
>> Good Idea, but using the same argument structure for set and get I would be
>> concerned about the loss of compiler protection for the buffer argument;
> Agreed, I missed that.

Sadly, the pattern of

struct getxattr_args args;

memset(&args, 0, sizeof(args));

args.xxxx = ...

__vfs_getxattr(&args};

...

__vfs_setxattr(&args);

would be nice, so maybe we need to cool our jets and instead:

struct xattr_gs_args {
	struct dentry *dentry;
	struct inode *inode;
	const char *name;
	union {
	        void *buffer;
	        const void *value;
	};
	size_t size;
	int flags;
};

value _must_ be referenced for all setxattr operations, buffer for getxattr operations (how can we enforce that?).

>> struct getxattr_args {
>> 	struct dentry *dentry;
>> 	struct inode *inode;
>> 	const char *name;
>> 	void *buffer;
>> 	size_t size;
>> 	int flags;
> Does 'get' need flags?
>
:-) That was the _whole_ point of the patch, flags is how we pass in the 
recursion so that a security/internal getxattr call has the rights to 
acquire the data in the lower layer(s).

-- Mark