On Tue, 18 Feb 2014 15:16:50 -0800
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Sun, 16 Feb 2014 20:31:01 +0800 Fabian Frederick <fabf@xxxxxxxxx> wrote:
>
> > Any user can display extented attribute names without read
> > access.
> >
> > eg: attr -l <filename>
> >
> > This patch checks inode_permission in listxattr common
> > function before executing vfs_listxattr.
> >
> > ...
> >
> > --- a/fs/xattr.c
> > +++ b/fs/xattr.c
> > @@ -543,6 +543,10 @@ listxattr(struct dentry *d, char __user *list, size_t size)
> > char *klist = NULL;
> > char *vlist = NULL; /* If non-NULL, we used vmalloc() */
> >
> > + error = inode_permission(d->d_inode, MAY_READ);
> > + if (error)
> > + return error;
> > +
> > if (size) {
> > if (size > XATTR_LIST_MAX)
> > size = XATTR_LIST_MAX;
>
> erk. Doesn't this mean that if existing userspace is relying on the
> current behaviour, this patch will cause breakage?
>
IMHO userspace applications already receive weird results in that case.
Without read permission, attr -l receives attribute names which means
it tries lgetxattr on those attributes where result is EACCESS :
"Attribute <attribute name> has -1 byte" !!!
Besides, is it semantically correct for a user to have access to
a part of "file content" without read access ?
With that patch, attr -l <filename> displays
attr_list: Permission denied
Could not list "(null)" for <filename>
On the other hand, when stracing that situation,
I do see attr making more noise than usual ie it's opening all attr.mo
twice so I guess I should return something else than "permission denied" to avoid problems in userspace ...
Fabian
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