Messages in this thread Patch in this message | | | Date | Sun, 21 Dec 2003 01:40:39 -0800 | From | Ulrich Drepper <> | Subject | [PATCH] O_DIRECTORY|O_CREAT handling |
| |
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
The kernel currently handles open() calls with flags having at least O_DIRECTORY|O_CREAT set strangely (to say the least). It creates a regular file, completely ignoring the O_DIRECTORY bit. One can argue that open() does not perform any real checking on the parameters and that it is the programmers responsibility, but there is a twist.
Some programs create temporary directory which they afterward use as the working directory or changed root. I.e., we have code like this:
mkdir ("/some/dirRANDOM"); chdir ("/some/dirRANDOM");
or
mkdir ("/some/dirRANDOM"); fd = open ("/some/dirRANDOM", O_DIRECTORY); fchdir (fd);
or
mkdir ("/some/dirRANDOM"); chroot ("/some/dirRANDOM");
All these pieces of code have an obvious flaw, a race. There is no atomic way to do what we want.
Now combine these two problems. How about making this work?
fd = open ("/some/dirRANDOM", O_RDONLY|O_CREAT|O_DIRECTORY|O_EXCL, 0700); fchdir (fd);
(and similarly for a new interface fchroot which I can add to glibc).
I've attached a little patch which does just that. Some comments on the code:
~ if an existing directory is opened with O_RDWR open() returns - -EISDIR. I've mimicked this, allthough the error code might not be the most obvious.
~ O_TRUNC is not allowed.
The small attached patch implements this proposal. At least it does what I want it to do, no idea what bugs I introduce.
- -- ➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (GNU/Linux)
iD8DBQE/5WqW2ijCOnn/RHQRAjZEAJ9SxzM1O6B/hQZN5jabqSSzXXtZwQCdH2sd hRr+ejRNAU4Cl9V8MXpBIYo= =jXqY -----END PGP SIGNATURE----- --- linux-2.6/fs/namei.c-opendir 2003-12-20 21:32:50.000000000 -0800 +++ linux-2.6/fs/namei.c 2003-12-21 01:37:09.000000000 -0800 @@ -1295,7 +1295,12 @@ if (!dentry->d_inode) { if (!IS_POSIXACL(dir->d_inode)) mode &= ~current->fs->umask; - error = vfs_create(dir->d_inode, dentry, mode, nd); + if (unlikely(flag & O_DIRECTORY)) { + error = -EISDIR; + if (!(flag & FMODE_WRITE)) + error = vfs_mkdir(dir->d_inode, dentry, mode); + } else + error = vfs_create(dir->d_inode, dentry, mode, nd); up(&dir->d_inode->i_sem); dput(nd->dentry); nd->dentry = dentry; @@ -1331,7 +1336,11 @@ dput(nd->dentry); nd->dentry = dentry; error = -EISDIR; - if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) + /* Since we allow creating directories with open(2) we forbid + opening an existing directory with O_CREAT only if the + O_DIRECTORY flag is not set or if truncation is requested. */ + if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode) && + (!(flag & O_DIRECTORY) || (flag & O_TRUNC))) goto exit; ok: error = may_open(nd, acc_mode, flag); | |