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SubjectRe: Open by inode? (was Re: knfsd)
On Sat, Jan 09, 1999 at 01:02:47PM +0000, Alain Williams wrote:
> * Hack the file system code to handle a directory with an inode of
> 4 specially:
> * If you try to open a file in that directory the name
> will be interpretted as an inode number and yeild that file.
> * If you try to read (ie 'ls') the directory you get nothing.
> * If you try to write to the directory (ie 'rm') it fails.
> This has the advantage of needing no new system calls, just a small
> change to the ext2 file system code. It can be secure, the directory can
> be chowned/chgrped to limmit access, if the sysadmin doesn't want it at
> all (generally the case) he either removes the directory or doesn't
> create it in the first place.

I like this. I prefer an ext2 attribute on a directory.

The change to implement this is small, but a little bit fiddly. The
basic lookup by inode is easy, but making sure the dentries are
invalidated at the right times so we don't keep files around forever,
not going wrong with requests for deleted inodes etc. hits various
corners.

Patch enclosed against 2.2.0-pre4; give it a go.
To test, make a directory and pass its name to this program (compile
after applying the kernel patch):

#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/ext2_fs.h>

void main (int argc, char ** argv)
{
for (; *argv; argv++)
{
unsigned long flags;
int fd = open (*argv, O_RDONLY|O_NONBLOCK);
ioctl (fd, EXT2_IOC_GETFLAGS, &flags);
flags |= EXT2_IOPEN_FL;
ioctl (fd, EXT2_IOC_SETFLAGS, &flags);
close (fd);
}
}
Then you can open inodes in that directory by number. Any inode on the
same filesystem is opened. The directory always appears empty.

I still haven't a clue what use this is! :-)

Enjoy,
-- Jamie

--- linux/fs/ext2/dir.c.iopen Fri Nov 20 14:21:01 1998
+++ linux/fs/ext2/dir.c Sun Jan 10 06:25:53 1999
@@ -117,6 +117,8 @@

if (!inode || !S_ISDIR(inode->i_mode))
return -EBADF;
+ if (inode->u.ext2_i.i_flags & EXT2_IOPEN_FL)
+ goto treat_as_empty;
sb = inode->i_sb;

stored = 0;
@@ -215,6 +217,7 @@
offset = 0;
brelse (bh);
}
- UPDATE_ATIME(inode);
+treat_as_empty:
+ UPDATE_ATIME(inode);
return 0;
}
--- linux/fs/ext2/namei.c.iopen Sun Jan 3 07:55:30 1999
+++ linux/fs/ext2/namei.c Sun Jan 10 22:05:44 1999
@@ -16,6 +16,8 @@
* David S. Miller (davem@caip.rutgers.edu), 1995
* Directory entry file type support and forward compatibility hooks
* for B-tree directories by Theodore Ts'o (tytso@mit.edu), 1998
+ * Open by inode number support by
+ * Jamie Lokier <jamie@imbolc.ucc.ie>, 1999
*/

#include <asm/uaccess.h>
@@ -65,17 +67,22 @@
*/
static struct buffer_head * ext2_find_entry (struct inode * dir,
const char * const name, int namelen,
- struct ext2_dir_entry_2 ** res_dir)
+ struct ext2_dir_entry_2 ** res_dir,
+ int * err)
{
struct super_block * sb;
struct buffer_head * bh_use[NAMEI_RA_SIZE];
struct buffer_head * bh_read[NAMEI_RA_SIZE];
unsigned long offset;
- int block, toread, i, err;
+ int block, toread, i;

*res_dir = NULL;
+ *err = 0;
if (!dir)
return NULL;
+ *err = -EPERM;
+ if (dir->u.ext2_i.i_flags & EXT2_IOPEN_FL)
+ return NULL;
sb = dir->i_sb;

if (namelen > EXT2_NAME_LEN)
@@ -88,7 +95,7 @@

if ((block << EXT2_BLOCK_SIZE_BITS (sb)) >= dir->i_size)
break;
- bh = ext2_getblk (dir, block, 0, &err);
+ bh = ext2_getblk (dir, block, 0, err);
bh_use[block] = bh;
if (bh && !buffer_uptodate(bh))
bh_read[toread++] = bh;
@@ -156,7 +163,7 @@
dir->i_size)
bh = NULL;
else
- bh = ext2_getblk (dir, block + NAMEI_RA_SIZE, 0, &err);
+ bh = ext2_getblk (dir, block + NAMEI_RA_SIZE, 0, err);
bh_use[block % NAMEI_RA_SIZE] = bh;
if (bh && !buffer_uptodate(bh))
bh_read[toread++] = bh;
@@ -165,19 +172,68 @@
failure:
for (i = 0; i < NAMEI_RA_SIZE; ++i)
brelse (bh_use[i]);
+ *err = -ENOENT;
return NULL;
}

+static struct dentry_operations ext2_iopen_dentry_ops =
+{
+ NULL, NULL, NULL, d_drop /* d_delete */, NULL, NULL
+};
+
+static int ext2_lookup_by_inode (struct inode * dir,
+ struct dentry * dentry)
+{
+ struct inode * inode;
+ int err = -ENOENT;
+ unsigned long ino = 0;
+ const char * name = dentry->d_name.name;
+
+ while (*name) {
+ unsigned int ch = *name++ - '0';
+ if (ch > 9)
+ goto out;
+ if (ino > ~0UL / 10)
+ goto out;
+ ino = ino * 10 + ch;
+ if (ino < ch)
+ goto out;
+ }
+
+ inode = iget(dir->i_sb, ino);
+ if (!inode)
+ goto out;
+ if (inode->u.ext2_i.i_deleted) {
+ /*
+ * Without this we can do bad things like linking to
+ * deleted files without allocating the bitmaps.
+ */
+ iput(inode);
+ err = -EPERM;
+ goto out;
+ }
+ /* Such generosity; we let you reopen unlinked but still open files. */
+ dentry->d_op = &ext2_iopen_dentry_ops;
+ d_add(dentry, inode);
+ err = 0;
+ out:
+ return err;
+}
+
int ext2_lookup(struct inode * dir, struct dentry *dentry)
{
struct inode * inode;
struct ext2_dir_entry_2 * de;
struct buffer_head * bh;
+ int err;
+
+ if (dir->u.ext2_i.i_flags & EXT2_IOPEN_FL)
+ return ext2_lookup_by_inode (dir, dentry);

if (dentry->d_name.len > EXT2_NAME_LEN)
return -ENAMETOOLONG;

- bh = ext2_find_entry (dir, dentry->d_name.name, dentry->d_name.len, &de);
+ bh = ext2_find_entry (dir, dentry->d_name.name, dentry->d_name.len, &de, &err);
inode = NULL;
if (bh) {
unsigned long ino = le32_to_cpu(de->inode);
@@ -216,6 +272,9 @@
*res_dir = NULL;
if (!dir || !dir->i_nlink)
return NULL;
+ *err = -EPERM;
+ if (dir->u.ext2_i.i_flags & EXT2_IOPEN_FL)
+ return NULL;
sb = dir->i_sb;

if (namelen > EXT2_NAME_LEN)
@@ -623,9 +682,9 @@
goto out;

retval = -ENOENT;
- bh = ext2_find_entry (dir, dentry->d_name.name, dentry->d_name.len, &de);
+ bh = ext2_find_entry (dir, dentry->d_name.name, dentry->d_name.len, &de, &retval);
if (!bh)
- goto end_rmdir;
+ goto out;

inode = dentry->d_inode;
DQUOT_INIT(inode);
@@ -681,9 +740,9 @@
goto out;

retval = -ENOENT;
- bh = ext2_find_entry (dir, dentry->d_name.name, dentry->d_name.len, &de);
+ bh = ext2_find_entry (dir, dentry->d_name.name, dentry->d_name.len, &de, &retval);
if (!bh)
- goto end_unlink;
+ goto out;

inode = dentry->d_inode;
DQUOT_INIT(inode);
@@ -870,11 +929,12 @@
int retval;

old_bh = new_bh = dir_bh = NULL;
+
retval = -ENAMETOOLONG;
if (old_dentry->d_name.len > EXT2_NAME_LEN)
goto end_rename;

- old_bh = ext2_find_entry (old_dir, old_dentry->d_name.name, old_dentry->d_name.len, &old_de);
+ old_bh = ext2_find_entry (old_dir, old_dentry->d_name.name, old_dentry->d_name.len, &old_de, &retval);
/*
* Check for inode number is _not_ due to possible IO errors.
* We might rmdir the source, keep it as pwd of some process
@@ -882,13 +942,12 @@
* same name. Goodbye sticky bit ;-<
*/
old_inode = old_dentry->d_inode;
- retval = -ENOENT;
if (!old_bh || le32_to_cpu(old_de->inode) != old_inode->i_ino)
goto end_rename;

new_inode = new_dentry->d_inode;
new_bh = ext2_find_entry (new_dir, new_dentry->d_name.name,
- new_dentry->d_name.len, &new_de);
+ new_dentry->d_name.len, &new_de, &retval);
if (new_bh) {
if (!new_inode) {
brelse (new_bh);
--- linux/fs/ext2/ioctl.c.iopen Sun Jan 10 06:09:45 1999
+++ linux/fs/ext2/ioctl.c Sun Jan 10 11:14:28 1999
@@ -31,13 +31,13 @@
if (get_user(flags, (int *) arg))
return -EFAULT;
flags = flags & EXT2_FL_USER_MODIFIABLE;
- /*
- * The IMMUTABLE and APPEND_ONLY flags can only be changed by
- * the super user when the security level is zero.
- */
- if ((flags & (EXT2_APPEND_FL | EXT2_IMMUTABLE_FL)) ^
- (inode->u.ext2_i.i_flags &
- (EXT2_APPEND_FL | EXT2_IMMUTABLE_FL))) {
+ /*
+ * The IMMUTABLE, APPEND_ONLY and IOPEN flags can
+ * only be changed by the super user when the security
+ * level is zero.
+ */
+ if ((flags & EXT2_FL_MODIFY_NEEDS_SECURITY)
+ != (inode->u.ext2_i.i_flags & EXT2_FL_MODIFY_NEEDS_SECURITY)) {
/* This test looks nicer. Thanks to Pauline Middelink */
if (!capable(CAP_LINUX_IMMUTABLE))
return -EPERM;
--- linux/fs/ext2/ialloc.c.iopen Thu Nov 12 12:05:51 1998
+++ linux/fs/ext2/ialloc.c Sun Jan 10 10:00:11 1999
@@ -479,6 +479,7 @@
inode->i_blocks = 0;
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
inode->u.ext2_i.i_new_inode = 1;
+ inode->u.ext2_i.i_deleted = 0;
inode->u.ext2_i.i_flags = dir->u.ext2_i.i_flags;
if (S_ISLNK(mode))
inode->u.ext2_i.i_flags &= ~(EXT2_IMMUTABLE_FL | EXT2_APPEND_FL);
--- linux/fs/ext2/inode.c.iopen Sun Jan 10 09:57:01 1999
+++ linux/fs/ext2/inode.c Sun Jan 10 14:26:58 1999
@@ -48,9 +48,11 @@
void ext2_delete_inode (struct inode * inode)
{
if (inode->i_ino == EXT2_ACL_IDX_INO ||
- inode->i_ino == EXT2_ACL_DATA_INO)
+ inode->i_ino == EXT2_ACL_DATA_INO ||
+ inode->u.ext2_i.i_deleted)
return;
inode->u.ext2_i.i_dtime = CURRENT_TIME;
+ inode->u.ext2_i.i_deleted = 1;
mark_inode_dirty(inode);
ext2_update_inode(inode, IS_SYNC(inode));
inode->i_size = 0;
@@ -532,6 +534,7 @@
inode->i_blocks = le32_to_cpu(raw_inode->i_blocks);
inode->i_version = ++event;
inode->u.ext2_i.i_new_inode = 0;
+ inode->u.ext2_i.i_deleted = (raw_inode->i_links_count == 0);
inode->u.ext2_i.i_flags = le32_to_cpu(raw_inode->i_flags);
inode->u.ext2_i.i_faddr = le32_to_cpu(raw_inode->i_faddr);
inode->u.ext2_i.i_frag_no = raw_inode->i_frag;
--- linux/include/linux/ext2_fs.h.iopen Wed Jan 6 13:48:33 1999
+++ linux/include/linux/ext2_fs.h Sun Jan 10 04:53:00 1999
@@ -198,10 +198,12 @@
#define EXT2_ECOMPR_FL 0x00000800 /* Compression error */
/* End compression flags --- maybe not all used */
#define EXT2_BTREE_FL 0x00001000 /* btree format dir */
+#define EXT2_IOPEN_FL 0x00002000 /* open-by-inode dir */
#define EXT2_RESERVED_FL 0x80000000 /* reserved for ext2 lib */

-#define EXT2_FL_USER_VISIBLE 0x00001FFF /* User visible flags */
-#define EXT2_FL_USER_MODIFIABLE 0x000000FF /* User modifiable flags */
+#define EXT2_FL_USER_VISIBLE 0x00003FFF /* User visible flags */
+#define EXT2_FL_USER_MODIFIABLE 0x000020FF /* User modifiable flags */
+#define EXT2_FL_MODIFY_NEEDS_SECURITY 0x00002030 /* Iff CAP_LINUX_IMMUTABLE*/

/*
* ioctl commands
-
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