linux/fs/exportfs/expfs.c
Peter Staubach 8c7b389e53 [PATCH] NFS server subtree_check returns dubious value
Address a problem found when a Linux NFS server uses the "subtree_check"
export option.

The "subtree_check" NFS export option was designed to prohibit a client
from using a file handle for which it should not have permission.  The
algorithm used is to ensure that the entire path to the file being
referenced is accessible to the user attempting to use the file handle.  If
some part of the path is not accessible, then the operation is aborted and
the appropriate version of ESTALE is returned to the NFS client.

The error, ESTALE, is unfortunate in that it causes NFS clients to make
certain assumptions about the continued existence of the file.  They assume
that the file no longer exists and refuse to attempt to access it again.
In this case, the file really does exist, but access was denied by the
server for a particular user.

A better error to return would be an EACCES sort of error.  This would
inform the client that the particular operation that it was attempting was
not allowed, without the nasty side effects of the ESTALE error.

Signed-off-by: Peter Staubach <staubach@redhat.com>
Acked-By: NeilBrown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-05-21 12:59:16 -07:00

533 lines
14 KiB
C

#include <linux/fs.h>
#include <linux/file.h>
#include <linux/module.h>
#include <linux/smp_lock.h>
#include <linux/namei.h>
struct export_operations export_op_default;
#define CALL(ops,fun) ((ops->fun)?(ops->fun):export_op_default.fun)
#define dprintk(fmt, args...) do{}while(0)
static struct dentry *
find_acceptable_alias(struct dentry *result,
int (*acceptable)(void *context, struct dentry *dentry),
void *context)
{
struct dentry *dentry, *toput = NULL;
spin_lock(&dcache_lock);
list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) {
dget_locked(dentry);
spin_unlock(&dcache_lock);
if (toput)
dput(toput);
if (dentry != result && acceptable(context, dentry)) {
dput(result);
return dentry;
}
spin_lock(&dcache_lock);
toput = dentry;
}
spin_unlock(&dcache_lock);
if (toput)
dput(toput);
return NULL;
}
/**
* find_exported_dentry - helper routine to implement export_operations->decode_fh
* @sb: The &super_block identifying the filesystem
* @obj: An opaque identifier of the object to be found - passed to
* get_inode
* @parent: An optional opqaue identifier of the parent of the object.
* @acceptable: A function used to test possible &dentries to see if they are
* acceptable
* @context: A parameter to @acceptable so that it knows on what basis to
* judge.
*
* find_exported_dentry is the central helper routine to enable file systems
* to provide the decode_fh() export_operation. It's main task is to take
* an &inode, find or create an appropriate &dentry structure, and possibly
* splice this into the dcache in the correct place.
*
* The decode_fh() operation provided by the filesystem should call
* find_exported_dentry() with the same parameters that it received except
* that instead of the file handle fragment, pointers to opaque identifiers
* for the object and optionally its parent are passed. The default decode_fh
* routine passes one pointer to the start of the filehandle fragment, and
* one 8 bytes into the fragment. It is expected that most filesystems will
* take this approach, though the offset to the parent identifier may well be
* different.
*
* find_exported_dentry() will call get_dentry to get an dentry pointer from
* the file system. If any &dentry in the d_alias list is acceptable, it will
* be returned. Otherwise find_exported_dentry() will attempt to splice a new
* &dentry into the dcache using get_name() and get_parent() to find the
* appropriate place.
*/
struct dentry *
find_exported_dentry(struct super_block *sb, void *obj, void *parent,
int (*acceptable)(void *context, struct dentry *de),
void *context)
{
struct dentry *result = NULL;
struct dentry *target_dir;
int err;
struct export_operations *nops = sb->s_export_op;
struct dentry *alias;
int noprogress;
char nbuf[NAME_MAX+1];
/*
* Attempt to find the inode.
*/
result = CALL(sb->s_export_op,get_dentry)(sb,obj);
err = -ESTALE;
if (result == NULL)
goto err_out;
if (IS_ERR(result)) {
err = PTR_ERR(result);
goto err_out;
}
if (S_ISDIR(result->d_inode->i_mode) &&
(result->d_flags & DCACHE_DISCONNECTED)) {
/* it is an unconnected directory, we must connect it */
;
} else {
if (acceptable(context, result))
return result;
if (S_ISDIR(result->d_inode->i_mode)) {
err = -EACCES;
goto err_result;
}
alias = find_acceptable_alias(result, acceptable, context);
if (alias)
return alias;
}
/* It's a directory, or we are required to confirm the file's
* location in the tree based on the parent information
*/
dprintk("find_exported_dentry: need to look harder for %s/%d\n",sb->s_id,*(int*)obj);
if (S_ISDIR(result->d_inode->i_mode))
target_dir = dget(result);
else {
if (parent == NULL)
goto err_result;
target_dir = CALL(sb->s_export_op,get_dentry)(sb,parent);
if (IS_ERR(target_dir))
err = PTR_ERR(target_dir);
if (target_dir == NULL || IS_ERR(target_dir))
goto err_result;
}
/*
* Now we need to make sure that target_dir is properly connected.
* It may already be, as the flag isn't always updated when connection
* happens.
* So, we walk up parent links until we find a connected directory,
* or we run out of directories. Then we find the parent, find
* the name of the child in that parent, and do a lookup.
* This should connect the child into the parent
* We then repeat.
*/
/* it is possible that a confused file system might not let us complete
* the path to the root. For example, if get_parent returns a directory
* in which we cannot find a name for the child. While this implies a
* very sick filesystem we don't want it to cause knfsd to spin. Hence
* the noprogress counter. If we go through the loop 10 times (2 is
* probably enough) without getting anywhere, we just give up
*/
noprogress= 0;
while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) {
struct dentry *pd = target_dir;
dget(pd);
spin_lock(&pd->d_lock);
while (!IS_ROOT(pd) &&
(pd->d_parent->d_flags&DCACHE_DISCONNECTED)) {
struct dentry *parent = pd->d_parent;
dget(parent);
spin_unlock(&pd->d_lock);
dput(pd);
pd = parent;
spin_lock(&pd->d_lock);
}
spin_unlock(&pd->d_lock);
if (!IS_ROOT(pd)) {
/* must have found a connected parent - great */
spin_lock(&pd->d_lock);
pd->d_flags &= ~DCACHE_DISCONNECTED;
spin_unlock(&pd->d_lock);
noprogress = 0;
} else if (pd == sb->s_root) {
printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n");
spin_lock(&pd->d_lock);
pd->d_flags &= ~DCACHE_DISCONNECTED;
spin_unlock(&pd->d_lock);
noprogress = 0;
} else {
/* we have hit the top of a disconnected path. Try
* to find parent and connect
* note: racing with some other process renaming a
* directory isn't much of a problem here. If someone
* renames the directory, it will end up properly
* connected, which is what we want
*/
struct dentry *ppd;
struct dentry *npd;
mutex_lock(&pd->d_inode->i_mutex);
ppd = CALL(nops,get_parent)(pd);
mutex_unlock(&pd->d_inode->i_mutex);
if (IS_ERR(ppd)) {
err = PTR_ERR(ppd);
dprintk("find_exported_dentry: get_parent of %ld failed, err %d\n",
pd->d_inode->i_ino, err);
dput(pd);
break;
}
dprintk("find_exported_dentry: find name of %lu in %lu\n", pd->d_inode->i_ino, ppd->d_inode->i_ino);
err = CALL(nops,get_name)(ppd, nbuf, pd);
if (err) {
dput(ppd);
dput(pd);
if (err == -ENOENT)
/* some race between get_parent and
* get_name? just try again
*/
continue;
break;
}
dprintk("find_exported_dentry: found name: %s\n", nbuf);
mutex_lock(&ppd->d_inode->i_mutex);
npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
mutex_unlock(&ppd->d_inode->i_mutex);
if (IS_ERR(npd)) {
err = PTR_ERR(npd);
dprintk("find_exported_dentry: lookup failed: %d\n", err);
dput(ppd);
dput(pd);
break;
}
/* we didn't really want npd, we really wanted
* a side-effect of the lookup.
* hopefully, npd == pd, though it isn't really
* a problem if it isn't
*/
if (npd == pd)
noprogress = 0;
else
printk("find_exported_dentry: npd != pd\n");
dput(npd);
dput(ppd);
if (IS_ROOT(pd)) {
/* something went wrong, we have to give up */
dput(pd);
break;
}
}
dput(pd);
}
if (target_dir->d_flags & DCACHE_DISCONNECTED) {
/* something went wrong - oh-well */
if (!err)
err = -ESTALE;
goto err_target;
}
/* if we weren't after a directory, have one more step to go */
if (result != target_dir) {
struct dentry *nresult;
err = CALL(nops,get_name)(target_dir, nbuf, result);
if (!err) {
mutex_lock(&target_dir->d_inode->i_mutex);
nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf));
mutex_unlock(&target_dir->d_inode->i_mutex);
if (!IS_ERR(nresult)) {
if (nresult->d_inode) {
dput(result);
result = nresult;
} else
dput(nresult);
}
}
}
dput(target_dir);
/* now result is properly connected, it is our best bet */
if (acceptable(context, result))
return result;
alias = find_acceptable_alias(result, acceptable, context);
if (alias)
return alias;
/* drat - I just cannot find anything acceptable */
dput(result);
/* It might be justifiable to return ESTALE here,
* but the filehandle at-least looks reasonable good
* and it just be a permission problem, so returning
* -EACCESS is safer
*/
return ERR_PTR(-EACCES);
err_target:
dput(target_dir);
err_result:
dput(result);
err_out:
return ERR_PTR(err);
}
static struct dentry *get_parent(struct dentry *child)
{
/* get_parent cannot be supported generically, the locking
* is too icky.
* instead, we just return EACCES. If server reboots or inodes
* get flushed, you lose
*/
return ERR_PTR(-EACCES);
}
struct getdents_callback {
char *name; /* name that was found. It already points to a
buffer NAME_MAX+1 is size */
unsigned long ino; /* the inum we are looking for */
int found; /* inode matched? */
int sequence; /* sequence counter */
};
/*
* A rather strange filldir function to capture
* the name matching the specified inode number.
*/
static int filldir_one(void * __buf, const char * name, int len,
loff_t pos, ino_t ino, unsigned int d_type)
{
struct getdents_callback *buf = __buf;
int result = 0;
buf->sequence++;
if (buf->ino == ino) {
memcpy(buf->name, name, len);
buf->name[len] = '\0';
buf->found = 1;
result = -1;
}
return result;
}
/**
* get_name - default export_operations->get_name function
* @dentry: the directory in which to find a name
* @name: a pointer to a %NAME_MAX+1 char buffer to store the name
* @child: the dentry for the child directory.
*
* calls readdir on the parent until it finds an entry with
* the same inode number as the child, and returns that.
*/
static int get_name(struct dentry *dentry, char *name,
struct dentry *child)
{
struct inode *dir = dentry->d_inode;
int error;
struct file *file;
struct getdents_callback buffer;
error = -ENOTDIR;
if (!dir || !S_ISDIR(dir->i_mode))
goto out;
error = -EINVAL;
if (!dir->i_fop)
goto out;
/*
* Open the directory ...
*/
file = dentry_open(dget(dentry), NULL, O_RDONLY);
error = PTR_ERR(file);
if (IS_ERR(file))
goto out;
error = -EINVAL;
if (!file->f_op->readdir)
goto out_close;
buffer.name = name;
buffer.ino = child->d_inode->i_ino;
buffer.found = 0;
buffer.sequence = 0;
while (1) {
int old_seq = buffer.sequence;
error = vfs_readdir(file, filldir_one, &buffer);
if (error < 0)
break;
error = 0;
if (buffer.found)
break;
error = -ENOENT;
if (old_seq == buffer.sequence)
break;
}
out_close:
fput(file);
out:
return error;
}
static struct dentry *export_iget(struct super_block *sb, unsigned long ino, __u32 generation)
{
/* iget isn't really right if the inode is currently unallocated!!
* This should really all be done inside each filesystem
*
* ext2fs' read_inode has been strengthed to return a bad_inode if
* the inode had been deleted.
*
* Currently we don't know the generation for parent directory, so
* a generation of 0 means "accept any"
*/
struct inode *inode;
struct dentry *result;
if (ino == 0)
return ERR_PTR(-ESTALE);
inode = iget(sb, ino);
if (inode == NULL)
return ERR_PTR(-ENOMEM);
if (is_bad_inode(inode)
|| (generation && inode->i_generation != generation)
) {
/* we didn't find the right inode.. */
dprintk("fh_verify: Inode %lu, Bad count: %d %d or version %u %u\n",
inode->i_ino,
inode->i_nlink, atomic_read(&inode->i_count),
inode->i_generation,
generation);
iput(inode);
return ERR_PTR(-ESTALE);
}
/* now to find a dentry.
* If possible, get a well-connected one
*/
result = d_alloc_anon(inode);
if (!result) {
iput(inode);
return ERR_PTR(-ENOMEM);
}
return result;
}
static struct dentry *get_object(struct super_block *sb, void *vobjp)
{
__u32 *objp = vobjp;
unsigned long ino = objp[0];
__u32 generation = objp[1];
return export_iget(sb, ino, generation);
}
/**
* export_encode_fh - default export_operations->encode_fh function
* @dentry: the dentry to encode
* @fh: where to store the file handle fragment
* @max_len: maximum length to store there
* @connectable: whether to store parent information
*
* This default encode_fh function assumes that the 32 inode number
* is suitable for locating an inode, and that the generation number
* can be used to check that it is still valid. It places them in the
* filehandle fragment where export_decode_fh expects to find them.
*/
static int export_encode_fh(struct dentry *dentry, __u32 *fh, int *max_len,
int connectable)
{
struct inode * inode = dentry->d_inode;
int len = *max_len;
int type = 1;
if (len < 2 || (connectable && len < 4))
return 255;
len = 2;
fh[0] = inode->i_ino;
fh[1] = inode->i_generation;
if (connectable && !S_ISDIR(inode->i_mode)) {
struct inode *parent;
spin_lock(&dentry->d_lock);
parent = dentry->d_parent->d_inode;
fh[2] = parent->i_ino;
fh[3] = parent->i_generation;
spin_unlock(&dentry->d_lock);
len = 4;
type = 2;
}
*max_len = len;
return type;
}
/**
* export_decode_fh - default export_operations->decode_fh function
* @sb: The superblock
* @fh: pointer to the file handle fragment
* @fh_len: length of file handle fragment
* @acceptable: function for testing acceptability of dentrys
* @context: context for @acceptable
*
* This is the default decode_fh() function.
* a fileid_type of 1 indicates that the filehandlefragment
* just contains an object identifier understood by get_dentry.
* a fileid_type of 2 says that there is also a directory
* identifier 8 bytes in to the filehandlefragement.
*/
static struct dentry *export_decode_fh(struct super_block *sb, __u32 *fh, int fh_len,
int fileid_type,
int (*acceptable)(void *context, struct dentry *de),
void *context)
{
__u32 parent[2];
parent[0] = parent[1] = 0;
if (fh_len < 2 || fileid_type > 2)
return NULL;
if (fileid_type == 2) {
if (fh_len > 2) parent[0] = fh[2];
if (fh_len > 3) parent[1] = fh[3];
}
return find_exported_dentry(sb, fh, parent,
acceptable, context);
}
struct export_operations export_op_default = {
.decode_fh = export_decode_fh,
.encode_fh = export_encode_fh,
.get_name = get_name,
.get_parent = get_parent,
.get_dentry = get_object,
};
EXPORT_SYMBOL(export_op_default);
EXPORT_SYMBOL(find_exported_dentry);
MODULE_LICENSE("GPL");