Messages in this thread | | | Date | Wed, 19 Feb 2014 06:43:46 +0800 | From | Fabian Frederick <> | Subject | Re: [PATCH 1/1] fs: xattr: Don't display attributes without read access |
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On Tue, 18 Feb 2014 15:16:50 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
> On Sun, 16 Feb 2014 20:31:01 +0800 Fabian Frederick <fabf@skynet.be> 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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