Messages in this thread Patch in this message | | | Date | Thu, 13 May 2010 16:56:06 +1000 | From | Neil Brown <> | Subject | Re: [PATCH -V7 5/9] vfs: Add freadlink syscall |
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On Thu, 13 May 2010 11:55:56 +0530 "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
> On Thu, 13 May 2010 11:43:51 +1000, Neil Brown <neilb@suse.de> wrote: > > On Wed, 12 May 2010 21:20:40 +0530 > > "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> 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@suse.de> 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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