On Thu, 13 May 2010 11:55:56 +0530
"Aneesh Kumar K. V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
> On Thu, 13 May 2010 11:43:51 +1000, Neil Brown <neilb@xxxxxxx> wrote:
> > On Wed, 12 May 2010 21:20:40 +0530
> > "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> wrote:
> >
> > > This enables to use open-by-handle and then get the link target
> > > details of a symlink using the fd returned by handle
> > >
> >
> >
> > I find it very frustrating that a new syscall seems to be needed here.
> > We have 'readlinkat', and it should be enough.
> > How: the 'dfd' has to be a 'directory', and the path name as to be non-empty.
> >
> > The following patch allows 'path' to be NULL and in that case 'dfd' to be a
> > non-directory. This allows readlinkat and faccessat (and probably others)
> > to be used on an fd with not following path name.
> >
> > What do people think of this alternative?
> >
>
> I will add this in the next iteration and drop the freadlink syscall.
>
I wouldn't be quite that hasty. It was only a proposal. It might not be
appropriate to change all those syscalls..
An alternative that I don't think is a nice, but is a lot 'safer' is
to just change readlinkat to accept a NULL path:
Signed-off-by: NeilBrown <neilb@xxxxxxx>
diff --git a/fs/stat.c b/fs/stat.c
index c4ecd52..85d0856 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -284,26 +284,40 @@ SYSCALL_DEFINE2(newfstat, unsigned int, fd, struct stat __user *, statbuf)
SYSCALL_DEFINE4(readlinkat, int, dfd, const char __user *, pathname,
char __user *, buf, int, bufsiz)
{
- struct path path;
+ struct path path, *pp;
+ struct file *file = NULL;
int error;
if (bufsiz <= 0)
return -EINVAL;
- error = user_path_at(dfd, pathname, 0, &path);
+ if (filename == NULL && dfd != AT_FDCWD) {
+ struct file *file = fget(dfd);
+
+ if (file)
+ pp = &file->f_path;
+ else
+ error = -EBADF;
+ } else {
+ error = user_path_at(dfd, pathname, 0, &path);
+ pp = &path;
+ }
if (!error) {
- struct inode *inode = path.dentry->d_inode;
+ struct inode *inode = pp->dentry->d_inode;
error = -EINVAL;
if (inode->i_op->readlink) {
- error = security_inode_readlink(path.dentry);
+ error = security_inode_readlink(pp->dentry);
if (!error) {
- touch_atime(path.mnt, path.dentry);
- error = inode->i_op->readlink(path.dentry,
+ touch_atime(pp->mnt, pp->dentry);
+ error = inode->i_op->readlink(pp->dentry,
buf, bufsiz);
}
}
- path_put(&path);
+ if (file)
+ fput(file);
+ else
+ path_put(&path);
}
return error;
}
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